Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: SILVERGUN on February 03, 2016, 12:05:10 pm
-
I'm considering going back to a preamp/power amp configuration for my live rig. (Mesa Triaxis preamp) http://www.mesaboogie.com/amplifiers/electric/tube-pre-amplifiers/triaxis-programmable-pre-amp/index.html (http://www.mesaboogie.com/amplifiers/electric/tube-pre-amplifiers/triaxis-programmable-pre-amp/index.html)
I played through this for years and got spoiled by the programmability and MIDI functionality. There is nothing like hitting #1 on the floorboard and having everything change all at once.(instead of tap-dancing across multiple stompboxes and amp channel switches)
I'll have a wide variety of music to cover and I really prefer a wide pallet of different tones. When I play live I am playing for me, so it has to sound like what I want to hear. I know the crowd cant tell the difference (Ed).Solid state/modeling is out of the question.
I'm also considering building the power amp as a stereo SE EL34 configuration @ approx. 12 watts per side.
Thinking about individual toroids for each channel for PTs (with SS FWB should get me in the low 300s VDC for loaded B+):
http://www.antekinc.com/as-05t240-50va-240v-transformer/ (http://www.antekinc.com/as-05t240-50va-240v-transformer/)
And maybe these for OTs:
http://www.classictone.net/40-18031.html (http://www.classictone.net/40-18031.html)
http://www.classictone.net/40-18031.pdf (http://www.classictone.net/40-18031.pdf)
I'm mostly concerned about full output current requirements, because I imagine I'll be running both sides close to full out most of the night with overdrive. The Classic Tone OT is spec'd at 70mA which is right around idle for SE EL34,,right?
- And, I imagine 12+ watts out of an overdriven EL34 pushes much more than 70mA?
- Is OT probably just being conservatively rated and I should be fine or am I risking core saturation and crappy tone as a result?
- Should I just "buck up" and go for something like a Hammond 125GSE (Edcor, etc?)
- PTs have a .1 amp (100mA) rating for the HT windings...is that enough?
The whole reason to do it this way would be to get the benefit of SE tone (harmonic content) and have a wet/dry mix going through a single 2x12 cab where wet goes into one speaker and dry feeds the other. Power amp would basically be on high output setting all of the time and volume would be controlled by programmable preamp settings. Looking to push EL34s for best sound.
Power amp won't weigh a ton or cost a fortune and power tubes will be mounted horizontally for space savings in a rack/head that I will build. Triaxis/one rack effects processor/power amp all in one head cab.
Thanks for reading and thanks in advance for the help. This project will come together pretty quickly once I iron out the bumps and commit.
-
OK, gave it some more thought and realized I am creating my own current problem by keeping the B+ that low.
Maybe we use these and wind up around 440VDC unloaded
This model reduces available current from the PT to 80mA (this is the 50VA product line)
http://www.antekinc.com/as-05t320-50va-320v-transformer/ (http://www.antekinc.com/as-05t320-50va-320v-transformer/)
Next step up would be 100VA product line and is a significant size difference. But I'm seeing 2 separate 350V windings.
Would it be a good idea to use the second winding as a dedicated screen supply?
http://www.antekinc.com/as-1t350-100va-350v-transformer/ (http://www.antekinc.com/as-1t350-100va-350v-transformer/)
I guess I need help thinking clearly.
-
Phillips tube chart for single tube class A shows 265 supply voltage > 250 Plate volts; screen + plate draw @ idle is 80 - 115mA depending on configuration. If you run a quality 70mA tranny @ 50% over spec, that's 105mA, so you're maybe on the edge.
BTW my SE Champ & PP Princeton (latter since sold) sounded identical to me. I never heard the presence or absence of the second harmonic.
-
I think the TriAxis is a great preamp and I have a similar setup I used for years. When covering lots of material it is either this or carry 4 amps and 50 pedals. I have a Rocktron Voodoo Valve I use when asked to play where I may have to cover Van-Halen and Haggard. Southern folks are like that. That being said, I used to use a Marshall 50/50 which is a stereo 50 watter with ERL34's, but I it is rare that I could get it loud enough to enjoy the EL34 in Push Pull.
What I do now is very similar when I use the Rocktron. I built a SE EL34 that Dummyload designed. It is attached and will answer some of your questions. I do not like it with anything but overdrive/distortion. Chorus, Delay, verb, basically any modulation pedal doesn't sound quite right. Too much harmonic content and sort of gets mushy. But for one side of the stereo it works great. What I use for the clean side for mixing modulation effects is basically a Princeton. Basic Push Pull, 2 6v6 with a split load PI, which I find to handle clean well. I am running a 12AT7 PI tube.
I think you will be very close with 70Ma with a single tube EL34. I would feel better with a tad more. The transformer you have linked to may not give you enough headroom to play anything clean at club levels. That would be my only concern. It is very difficult to build a clubbing rig to cover all bases, but now days most of the time I am using a processor like the Voodoo Valve or I also have a JMP-1, I am only monitoring myself on stage. Most sound guys today will prefer a direct line out and the Voodoo has great cab simulation.
I simply consider the clean tone first since it is the most difficult to me.
I believe JoeJoe has an amp he calls the Cherry Bomb which is a SE EL34 that uses the Hammond transformer. Maybe he will jump in here. I did a search and did not come up with it.
Glad to see you are planning to play some. You are correct, the audience doesn't know generally. Still, you have to have something that inspires you to play. As they say "tone is in the hands". :laugh: So all you need is hands.
I am not trying to change your mind on anything as I like all my stuff all the way down to my Modded Boss DS-1. I just thought I would mention the lack of headroom may be an issue, but then again you can always mic up if needed for a larger venue.
-
BTW my SE Champ & PP Princeton (latter since sold) sounded identical to me. I never heard the presence or absence of the second harmonic.
Thanks for the input JJ....I was hoping that was not the case.
I was buying into the SE concept without much hands on experience.
I still have a PP Mesa Simul 395 that is a beast and is just too much amp to carry around.
Ed, did you link the wrong schematic?
-
I used to use a Marshall 50/50 which is a stereo 50 watter with ERL34's, but I it is rare that I could get it loud enough to enjoy the EL34 in Push Pull
That's exactly why I cant use the Mesa 395....overkill and just doesn't sound good when you choke it down to a point where you're not blowing people's hair back.
I was hoping to just run 2- EL34s flat out and that would allow me to get the richness of sound compared to 8- 6L6s being held way back.
I like the idea of something designed by DL.
-
What I do now is very similar when I use the Rocktron. I built a SE EL34 that Dummyload designed. It is attached and will answer some of your questions. I do not like it with anything but overdrive/distortion. Chorus, Delay, verb, basically any modulation pedal doesn't sound quite right. Too much harmonic content and sort of gets mushy. But for one side of the stereo it works great. What I use for the clean side for mixing modulation effects is basically a Princeton. Basic Push Pull, 2 6v6 with a split load PI, which I find to handle clean well. I am running a 12AT7 PI tube.
I guess there is another solution in there...
A mixed power amp where one channel is setup to enhance dry and the other to handle wet.
?
-
Sorry, I did link the wrong schematic. I think this is the one. :new1:
-
What I do now is very similar when I use the Rocktron. I built a SE EL34 that Dummyload designed. It is attached and will answer some of your questions. I do not like it with anything but overdrive/distortion. Chorus, Delay, verb, basically any modulation pedal doesn't sound quite right. Too much harmonic content and sort of gets mushy. But for one side of the stereo it works great. What I use for the clean side for mixing modulation effects is basically a Princeton. Basic Push Pull, 2 6v6 with a split load PI, which I find to handle clean well. I am running a 12AT7 PI tube.
I guess there is another solution in there...
A mixed power amp where one channel is setup to enhance dry and the other to handle wet.
?
This is the way I always play, even when playing at home. I have tried loops and like them for some things, but to me nothing beats 2 amps. If I am playing a traditional country gig, I use the AC15 for my OD side as it is so easy to push it into distortion and a Princeton Reverb that handles clean and modulation effects. I do like the AC15 Vibrato, but it works well with overdrive.
I prefer it so much that I even have what I call my mini-stack. That is a Champ on top of a 6 watt Gibson.
-
stereo SE EL34 configuration @ approx. 12 watts per side.
I was hoping to just run 2- EL34s flat out and that would allow me to get the richness of sound compared to 8- 6L6s being held way back
I don't think there is anyway to get 2 EL34's to do the job of what 4 (or even 8) 6L6's would do. If this is a gig rig, don't you want at least 40-50W in each channel?
If you are trying to save weight, 6L6s over EL34s save you PR iron weight. A shared PT would save weight too.. Is two bandmaster 2x6L6 pairs w/ OTs too straight forward? 2 12AT7's 4 6L6's, two OTs, and maybe one big PT for showman/twin?
If that's too much weight and output, then I'd scale it down to four 6v6's, 2 smaller OTs and one smaller PT..
-
Ithink this is the one
OK, thanks...I can see where that might only be good for OD
I was thinking something much simpler, like a parallel 12AU7 pushing a single EL34 per side (?)
The Triaxis can put out a pretty hot signal so I'm thinking the AU7 can handle that without clipping and "maybe" swing enough signal to get the ELs going?
-
I don't think there is anyway to get 2 EL34's to do the job of what 4 (or even 8) 6L6's would do. If this is a gig rig, don't you want at least 40-50W in each channel?
This won't be like my gig rigs of the past. I'm tired of being too loud and we will be doing classier tunes at restaurant/bar volumes.
It's much more important that it sounds really good to me. Read above where Ed and I talk about having a high power amp and throttling it back,,,just comes off sounding dead/flat.
If you are trying to save weight, 6L6s over EL34s save you PR iron weight. A shared PT would save weight too.. Is two bandmaster 2x6L6 pairs w/ OTs too straight forward? 2 12AT7's 4 6L6's, two OTs, and maybe one big PT for showman/twin?
All that "would be" OK, but I would probably just wind up using my 395 at that point
My original thought was that I "might" get better sound by smoking 2 EL34's ...and I also thought SE would be buying me something in the tone department.
How about SE KT88s?
-
ed, that schematic that looks like a PP output stage and not a SE?
--pete
-
ed, that schematic that looks like a PP output stage and not a SE?
We got him fixed up DL.....too much preamp in the correct one he posted though (see reply #7)
Got anything for SE big bottle power amp with simple big swing drive stage?
Or, wanna talk me out of it?...or into anything else
2 separate 1x12" combos that are just setup as power stages aren't out of the question either
-
Here's a thrown together proposed mockup for each channel...
-
That seems nice and simple and easily meets my KISS principle. :l2:
Everything is labeled except the first two resistors at the top. :dontknow:
Oh, and the cathode resistor on the EL34.
-
> an overdriven EL34 pushes much more than 70mA?
If the load is correctly chosen, ideally the current does not increase from idle to utter clipping.
With real tubes and conventional audio amp design, current goes up 10%-20%. EL34 will be on the high end of that range because the (useless) screen current goes way up when plate is slammed low.
I do think that any reasonable SE amp is a home (no drummer) amp, can be much heavier than a P-P amp, and doubling-up may hurt your back more than it helps the music. As jjasilli says, if you are gonna slam the piss out of it, the 2nd is totally drowned-out by the 3rd. P-P will make 3rd lighter and cheaper than SE.
Literal 12W is not a reasonable expectation for a gig-worthy SE EL34. That assumes 40% efficiency and running 30.0W Pdiss. I had a hard time matching B+ and load to get 13W out of 6550 working at 39W Pdiss. Yes, at high THD it was 17W, and totally-bent-square it was 21W out, but IMHO an audio amp should be rated for "clean", with overdrive more-or-less assumed.
-
That seems nice and simple and easily meets my KISS principle.
Everything is labeled except the first two resistors at the top.
Oh, and the cathode resistor on the EL34.
Thanks for having a look Paul.
I needed these guys to help me fill in those blanks...
But PRR just gave me some priceless clarity. His scientifically formed opinion is exactly what I was looking for.
Even though it wasn't what I wanted to hear.
He's got me leaning towards 2 small PP power amps, maybe built into their own 1x12" cabinets (just to lower the number of trips back and forth from my truck)
-
Hi SG! :icon_biggrin:
I know you have a preamp already but Tubenit (and Geezer) built several low powered PP K biased amps that you could maybe just nab the power section? Because of the K bias they would settle in by themselves.
They were able to change the rectifier tube (5Y3/5V4/GZ34?) to change B+ and with that change the power tubes (6K6/6V6/6L6GB?) to get a little less/more power.
-
So if I move towards PP I'll probably use the Mesa 50/50 as a template.
But to reduce output I'll drop the B+ and go with cathode biasing....maybe even build in VVR (based on your opinions)
I'm also still thinking about changing the input stage so that it will be less likely to clip the big incoming signal.
How do you like that parallel AU7 stage on my SE schematic?
On the load line that would appear to take a huge input signal with a 300V supply, 22K plate load and 2.7K cath R
My question would be if there is enough gain there for it to make sense?.....and is there any chance it will improve the performance with the Triaxis?
In the past I could never get the Triaxis output dual pot past 3 without seeming like I was overloading the inputs of the Simul 395
-
Hi SG! :icon_biggrin:
I know you have a preamp already but Tubenit (and Geezer) built several low powered PP K biased amps that you could maybe just nab the power section? Because of the K bias they would settle in by themselves.
They were able to change the rectifier tube (5Y3/5V4/GZ34?) to change B+ and with that change the power tubes (6K6/6V6/6L6GB?) to get a little less/more power.
Thanks Brad,
Thats how I'm leaning now but probably SS rect with VVR to play around with B+
-
I think you want NFB, a cathodyne or LTPI, a pair of 6L6s and a 20W deluxe OT (on each channel). look at an Ampeg Gemini output section or a BF Bandmaster output section. for me, the cathodyne is a fav for such a project b/c the first stage is an gain stage, and you can easily set the input impedance where you want to match your pre-amps (without thinking much about it...) and no fooling with a coupling cap.. (like you'd do with an LTPI)...
-
I'm also still thinking about changing the input stage so that it will be less likely to clip the big incoming signal.
How do you like that parallel AU7 stage on my SE schematic?
I'm still a newbie here, so.
I was looking at a few simple PP 6L6 circuits to try out.
That is when I first noticed any parallel pre-amp tube wiring.
I'm not sure what is accomplished by this, but in the circuits I was looking at they were only using 3 of the 4 stages available in 2 pre-amp tubes anyway.
I also have picked up on the fact that Hi-Fi tube amps tend to use a 6DJ8/6922 where the guitar amps go with 12A_7 varieties instead.
I know they want very low THD numbers from their amps compared to ours.
I don't know if that 6DJ8/6922 is a tube to be considered in achieving your goals or not. :dontknow:
-
PRR just gave me some priceless clarity
He is correct, fwiw, I built a SE that I *ballparked* for KT88, 6550 and EL34, the KT won out. it's running at 93% max, yields about 16W clean, 23 dimed. My son uses it for light jazz in a up-scale restaurant. I used a Hammond 25w UL OT.
-
If your not opposed to using a SS PA or powered speakers with a small mixer- I've recently been pondering the viability of PRR's 1/3 watt amp design somewhere on this Forum and coupling it to a 600 ohm matching transformer so that the output could be lined to a mixer. I haven't looked at this much yet so maybe it's a Hare Brain Idea.
Here is one link that popped up: http://el34world.com/Forum/index.php?topic=12454.msg115958#msg115958 (http://el34world.com/Forum/index.php?topic=12454.msg115958#msg115958)
silverfox.
-
attached is a 35W/ch amp using EL34.
B+ called for in datasheets is 375V and Ra-a at 3.4K. here we have slightly higher B+ but we also have slightly higher Ra-a so should be a wash. idle current is 346mA or thereabouts.
i really need to bread board it, but i'm confident it'll work. should fit in 3U rack chassis 16"-17" deep.
a couple of stringers: 1) need to hash NFB value. 2) considering adding a presence control rather than fixed NFB.
assuming we need higher input sensitivity, we swap V1 for 12AT7 or 12AX7 & replace V1 plate Rs w/ 100K & change R3 to 22K 1/2W.
the power iron is buckish, but hey, at least it's world power-grid friendly and anti-green.
if y'all see any errors, please post up. i'm sure you will... :icon_biggrin:
--pete
-
Pete,
That looks to be a great amp! You always come up with fantastic ideas. Bravo.
Silvergun, nice to see you on the forum!
With respect, Tubenit
-
attached is a 35W/ch amp using EL34.
Thanks for that DL.!!...looks great and maybe I'll put one channel on my board first
I'm leaning more towards 2 separate cabs with one power amp channel and a 12"er in each...basically "powered speakers"
-
Pete,
That looks to be a great amp! You always come up with fantastic ideas. Bravo.
Silvergun, nice to see you on the forum!
With respect, Tubenit
Yeah he does....
And thanks T...It's good to be seen...you guys are the best...all of you
-
attached is a 35W/ch amp using EL34.
Thanks for that DL.!!...looks great and maybe I'll put one channel on my board first
I'm leaning more towards 2 separate cabs with one power amp channel and a 12"er in each...basically "powered speakers"
good to see you back, SG.
that changes things with the power supply. considerably. back to the drawing board... :icon_biggrin:
--pete
-
see attached - PT, diodes, caps, and misc. power rail R values changed, changed choke. for 120V/60Hz only option use hammond 272HX.
--pete
-
THANKS again Pete!
To save some dough and use some stuff I have on hand I'll probably use Doug's stout chassis(s) and 2 PTs I have laying around.
They are 240VAC secondaries (no CT)@ 570mA and it only takes a slight mod to get them in the hole that's already there, and I've got 2 separate filament xfmrs.
So that should put unloaded B+ around 350ish, and it shouldn't budge much. With that lowered B+ I imagine we will enjoy the availability of all that current capacity. (?)
I also have a Hammond 1760L OT that's looking for a home 50watts @ 4.2K into 4/8/16 (we can mismatch to half the pri. if you suggest)
I'm thinking about using a different OT for one and maybe doing one pair EL34 and one pair 6L6 (or KT88 for fun)
Thanks again for all of your hard work and please don't spend too much time on me until I make up my mind.
But ALL input is much appreciated and taken into consideration. I think this will be a great use for those chassis.
Does anyone think I will hear a benefit if I set them up for two different output tube types?
-
Question,
I'm still pretty new, so take that with a grain of salt :)
If you're going for a lower output, why not try a tube like the EL84? I think they're each about 7 Watts max if done right, so for two in P-P it would be 14 Watts, and you could dial that down just like you're talking about.
Or do you just prefer the tone of the tubes you're working with/talking about better?
~Phil
-
Question,
I'm still pretty new, so take that with a grain of salt :)
If you're going for a lower output, why not try a tube like the EL84? I think they're each about 7 Watts max if done right, so for two in P-P it would be 14 Watts, and you could dial that down just like you're talking about.
Or do you just prefer the tone of the tubes you're working with/talking about better?
~Phil
Yeah, I just prefer the bigger tube tone...and I don't really need to go too quiet...it's a fine line between too loud and drowned out
And like PRR mentioned, I will still need to get over a drummer...that got me thinking about 30w in stereo
In the end, I might just drop a few db's by using less efficient speakers...we'll see
-
ahh makes perfect sense.
My AC30 with 4 of the EL84's in p-p has some spank to it, but I do know the EL34's have a bit more than that as well. :)
I'm still learning about what kinds of tonalities each of the tubes have and when might be a time to use tube X.
~Phil
-
with only 330V B+, perhaps you should consider a quad of 6V6GT. they don't sizzle like the EL84 and they are IMO, a smoother sounding tube than the 6L6Gx family. drive requirements are about 2x that of the EL84. IMO, in this scenario, fixed bias provides best tone.
drive 3.8k load (marshall 50W OT) with 4 6V6GT loafing at 330V you'll make ~30W. big tube sound with 4 little(r) bottles. use all octal toobz including preamplifier... 6SN7 LTPI and 6SN7 1st gain stage.
--pete
-
with only 330V B+, perhaps you should consider a quad of 6V6GT. they don't sizzle like the EL84 and they are IMO, a smoother sounding tube than the 6L6Gx family. drive requirements are about 2x that of the EL84. IMO, in this scenario, fixed bias provides best tone.
drive 3.8k load (marshall 50W OT) with 4 6V6GT loafing at 330V you'll make ~30W. big tube sound with 4 little(r) bottles. use all octal toobz including preamplifier... 6SN7 LTPI and 6SN7 1st gain stage.
--pete
Uh-oh...option overload... I'm gonna give it some serious thought and try to stick to one solution...I already had the AU7s pulled out onto the bench for excitement (those I have here...6SNs will cost me and have to get here)
I'm not locked into those transformers for this job, so if B+ needs to be higher for best results with 6L6/EL34, I might just invest....
I'm gonna take a couple days and get the board up and running and see where I am.
I'm slowly talking myself into the idea of mixing one side 6L6 and the other EL34 and then just see which does the dry/wet better than the other
I am pretty convinced now about these as just separate little power amps in the stout chassis, because I sat one on my thiele cab and it fit perfectly with the width of that cab....I already have the plywood cut for an identical cab so I'm thinking of mounting (or temp mount) or piggybacking these to the top of those cabs and just finish off the tops with a wood cap. (or robot helmet, etc..)....(kills 2 with 1....solves the cabinet issue and makes my decision for me)...they will be heavy but not tooo bad.
Maybe leave the Eminence EM12 in one for the wet ,,and then figure out the speaker for the dry by trying them out together?..(good spot for a Creamback? jojo?)
Please stop me if I go too far off topic DL..................
-
Now that I've looked at that pic I'm starting to think that I could just try that little Deluxe Champ Reverb, and make a "power amp in" and switch the preamp tubes to AU7s.
Try that for one side with an EL34 in place of that 6V6 and just hear it.....hmmm
There's plenty of current avail. on that amp because I used those same PT and fil. transformers I mentioned earlier
It also has the Classic Tone 15W OT,,,so maaaaybe I'll see what happens with one side SE and the other PP??
...sorry DL...I ain't done thinkin yet
Ed, in your wet/dry rig, do you run your wet amp 'just as loud' as your dry amp?...or do you think it might be OK to have a SE side wet that is not as loud as the PP dry side?
-
Silvergun, you are starting to sound like me. :w2:
I want to make this, or maybe that, or what if I combined all three? :l2:
I'm just kidding you. :icon_biggrin:
But I did think you started out looking for a SE output sound? No???
If you are wanting SE that can compete with drums, that kind of narrows things down to a bigger bottle output tube. Right?
No EL84 or 6V6 SE output is going to work.
Then your preference of the sound of the output tube is probably more important than the max watts you can get from it.
Do you know if you like the sound of the EL34 better than a 6L6 or one of the other big output tubes?
If you know that you want SE output and that you like the sound of the EL34 best, then you can focus in on those designs to get the sound you're looking for. Maybe :w2:
:l2:
-
I play in small to medium size bars & venues. I find a PP small bottle amp to be way to loud. I agree that the drums rule the volume range. But if the drums are scaled to that size venue, then IMHO a Deluxe Reverb, e.g., is overkill. If the drum set is too big (loud), then no one in the venue will be able to hear themselves think. This may depend if you're putting on a concert, or providing more low key entertainment.
So, I agree with Silvergun that a stereo SE amp putting out a combined total of 12 - 20W can work fine.
Harmonic density aside, stereo SE amps with big bottles can do that. (Personally I'd like to go with KT-88's, but what the heck.)
-
Silvergun, you are starting to sound like me. :w2:
I want to make this, or maybe that, or what if I combined all three? :l2:
I'm just kidding you. :icon_biggrin:
You got me Paul...there's always some truth to joking and I see where you're coming from...
Hopefully this will be a one shot deal for me and I can get back to actually playing guitar instead of talking about sound....
I started out thinking that I 'might' want to do SE, but after some input from the gallery (of very talented and knowledgeable folks) I have reconsidered..
But as we move through the thread I realize that the extent of possibilities is only limited by my imagination and desire to push.
There are a couple of things that we have resolved:
- I will use 2 of Doug's Stout chassis (I already have 1 here)
- I have backed away from the stereo SE (rackmount) idea and am leaning more towards 2 individual power amps with different qualities
- I've never heard 6V6s do what I want so I'm sticking to either 6L6, EL34, or KT88 (because I have them on hand), and probably 12AU7s as driver tubes because of their ability to handle big signal (and I've got some nice ones here)
-
^ +1
Even if you have a drummer, most places are not going to allow the drummer or band to get loud these days. For instance, I play small place every other weekend pretty much. The drummer is either using brushes of just letting the sticks drop. In this case a Princeton Stock can be too loud. The ONLY time I get to ever use big bottle amps anymore is outside festival gigs, and even then I don't really need to. I like to tho as I don't get a chance to often to use them outside my amp room.
I don't know where you will be playing, but most Bars these days around town are 5,000 sq foot or less. Stop by guitar center and plug into a Deluxe Reverb in the middle of the store and turn it up to about 5 where it should be played and see how pissed everyone in the store gets.
This is the problem with trying to build a rig that will work everywhere. For instance, if I play at the Brickhouse which is a Restaurant that turns to a Bar at 10 pm. Playing starts at 9. The first 2 sets are played at background volumes and traditionally all the ballads are played during dinner time. After the "family" crowd leaves and the average age becomes thirtysomethings and old drunks, then we can rock. Even then my amps sit behind plexiglass.
We also have a set of Roland V Drums and use them to play Irish Restaurant and I am using my mini stack which is a 6 watt Gibson and a Tweed Champ. I only know of 3 places in my area that have live music where the venue is large enough to use a 50 watt amp.
When the venue is large enough for bigger amps they usually have a sound system and you can mic up. For instance, I went to see Marty Stewart who IMO has one of the best tones in Country. It was at The Smokey Mountain Theater and he was using a Princeton and Kenny was using a deluxe. There you can walk right up to the stage and Kenny's Deluxe was on 4 with Bass on 2 and treble on 6 and Marty's Princeton was on 6 with the Bass almost off and Treble on 7.
I have experienced about the same. I have also seen when bands turn up too early, people leave and they do not get hired anymore. In the 70's and 80's things were different as clubs were larger and music was louder. I just mentioned the I focus on getting a great clean tone and live with the fact that my overdrive is going to come from a pedal and or a small preamp tube.
I have seen it too many times. Just last weekend at a club called mixers group of aging long haired won't let go of the 80's come in and setup to play. During the third song I saw the lead player turn up his 50 watt Peavy and within minutes the Drummer and Bass Player jumped up as well. The second guitar player was using a 7 string with a Crate Blue Voodoo and a full stack.
I do not know what the 4th song they played was because the people I was with were not willing to take the punishment and scream at each other to hear.
All this being said, I have had problems using 2 SE amps and not having enough headroom. That is why I mentioned this. Of all the stuff I have to gig with the vast majority of the time is it is the AC15 and Princeton. El84's and 6V6's do not sound as good as 6L6's and EL34's to me either, but I do get called back to play whereas I can assure you the band I saw last weekend will not. They are called Broken Glass.
Just thought I would share my experience with current gigging. I believe jjasilli has found the same to be true. If I lived in Austin or Memphis things may be different.
-
I play in small to medium size bars & venues. I find a PP small bottle amp to be way to loud. I agree that the drums rule the volume range. But if the drums are scaled to that size venue, then IMHO a Deluxe Reverb, e.g., is overkill. If the drum set is too big (loud), then no one in the venue will be able to hear themselves think. This may depend if you're putting on a concert, or providing more low key entertainment.
So, I agree with Silvergun that a stereo SE amp putting out a combined total of 12 - 20W can work fine.
Harmonic density aside, stereo SE amps with big bottles can do that. (Personally I'd like to go with KT-88's, but what the heck.)
Thanks for stoping back JJ...
I'm thinking it might be cool to do 1 SE KT88 and 1 PP 6L6/EL34 with VVR
But since I can only build one amp at a time I will lay out the SE idea on my smaller breadboard and see where that gets me.
At some point I realized that this is why I built those boards in the first place, and I cant get attached to one circuit on the BB and allow it to block me from moving on....they should also be able to give me some real world volume answers. (it would be pretty funny to see a breadboard sitting on top of my speaker cab next to my drummer)
I'm gonna need help choosing a "best" OT and figure now is not the time to be cheap....Hammond 125GSE for KT88 (or what?)
Is it super silly to do low B+, high current?...like SE KT88 with 330V B+
...very loosely based off of the numbers below and whatever you guys can give me
-
Just thought I would share my experience with current gigging. I believe jjasilli has found the same to be true.
Thanks for all of that Ed...it has been quite some time since I've been out there, and the goal with this band is to not annoy people.
JJ mentioned "low key entertainment" and that's where I want to be, but I think reality will force something more like "moderate key entertainment"
We won't be a party band and I won't be covering VH....more smokey blues, soul, some classics....lounge 'y
I have already been in negotiations with my drummer to soften the hitting, deaden the kit, and I already have him surrounded in a movable Plexiglas surround...next step might be "adjusted" sticks (there seems to be some different options out there), last ditch effort will be an electronic kit.
The good news is, I plan on limiting this to one night a month in one or 2 clubs that I can choose from. So the rooms will really dictate the outcome.
My adventurous spirit tells me to see what an SE KT88 sounds like. (something like shooter's reply#23)
I'm wondering what ideal conditions will be and what kind of drive I will need to get one cooking (?)
-
Slightly off topic but proof that I do remember how to use my scope and meter:
I took that little amp in the picture and measured output wattage...
(I used an 8 ohm resistive load on the output. I connected a scope and a true RMS meter across the load. I have the amp set with volume and tone controls maxed. I put in a .5V signal and test at 400hz. I raise the gain control on the amp until the output waveform is at max amplitude, just as it starts to flatten out on the peaks. I take the voltage reading from the meter and calculate watts as voltage squared divided by 8 ohms. )
That came out to 5.5VAC x 5.5 = 30.25 / 8 (ohms) = 3.78 watts
new JJ 6V6S
Operating conditions at that output:
303VDC plate to K
298 screen to K
37 VDC across 1K cath. resistor @35mA
11W pdiss (?)
8K primary with 8 ohm load on 8 ohm tap
The point of this experiment was:
- to show you that this is not all talk
- to show you the 'relative' expected voltages if I wind up using one of these PTs
- AND to try out the KT88,,,but the problem there was that I also realized that this amp does NOT have the 15W OT in it, so it will not work for the quickie big bottle experiment.
And then I plugged it into a speaker cab to see just how loud 4 watts can be.... And, I did come to the conclusion that an SE KT88 operating around 15W ish clean "should be" plenty loud for this application....(and I can highlight that with a more efficient speaker if needed).
Before I buy an SE OT...any thoughts??...anyone want to donate one to science? (I'll post a 'wanted to buy' over on Doug's buy/sell/trade)
If I'm being really silly with the low B+ please say so, and I'll get over it, and we can move on. I'm imagining that it's a good way to keep the max. output down. (and again, I have these PTs here, and they can handle the current) But I guess we should resolve B+ before we try to pick primary K
I don't see any internet archived operating conditions for KT88 @ 290V plate ....is that because no one is dumb enough to do it?
-
I tend to be all over the map with my amp ideas. :laugh:
No harm in trying different ideas out on the breadboard, though.
If your not building something for a paying customer, there is no rush.
Take your time and explore your ideas. You might discover something new that the rest of us will be interested in. :icon_biggrin:
-
it will work.
with 6550/KT88 @ 300V you'll need about a 2K load. 2.5K is close enough and will work.
i have a one-electron UBT-2. it's 4.8K at 4/8/16 or 2.4K at 8/16/32. since you built the cabinets for us at such a great price, for you 25 bux plus ship if you want it. i have several so it's nothing that'll be missed. if your transformers are 240V sec. then you should see about 335VDC unloaded. loaded around 310V. MAX idle current through UBT-2 is 120mA - use caution!
http://www.one-electron.com/Trans/UBT2_10.pdf (http://www.one-electron.com/Trans/UBT2_10.pdf)
--pete
EDIT: added 6550 single tube parameter from GE spec. sheet.
-
I don't see any internet archived operating conditions for KT88 @ 290V plate ....is that because no one is dumb enough to do it?
Here's me trying to sound smartish... From the datasheet on the KT88, the max anode voltage is 800, and from the one I found 250 is average plate. The datasheet also shows that the most voltage you'd want to push is about 400V at a -4 V bias point. I would bet that -4 is way too cold of a bias to do you good per my understanding of bias...
If I understand some about design and spec sheets, 290 V should be perfectly fine if the typical is 250V:
http://free-hosting.infodiv.com/audiotube/power_tetrode/power_tetrode0034/kt88-jj2003.jpg (http://free-hosting.infodiv.com/audiotube/power_tetrode/power_tetrode0034/kt88-jj2003.jpg)
or are you talking more of some advanced topic I don't yet understand :)
Ignore me if I'm off in left field lol
~Phil
-
i have a one-electron UBT-2. it's 4.8K at 4/8/16 or 2.4K at 8/16/32. since you built the cabinets for us at such a great price, for you 25 bux plus ship if you want it. i have several so it's nothing that'll be missed. if your transformers are 240V sec. then you should see about 335VDC unloaded. loaded around 310V. MAX idle current through UBT-2 is 120mA - use caution!
http://www.one-electron.com/Trans/UBT2_10.pdf (http://www.one-electron.com/Trans/UBT2_10.pdf)
--pete
SOLD
I sincerely appreciate that offer and I would be have to be pretty slow to not take you up on it.
That thing is BADASS!
If for no other reason than I cant perform any experiments without an OT
I'll catch up with you on PM and Paypal
In the meantime I gotta get a parts order going......
-
If I understand some about design and spec sheets, 290 V should be perfectly fine if the typical is 250V:
http://free-hosting.infodiv.com/audiotube/power_tetrode/power_tetrode0034/kt88-jj2003.jpg (http://free-hosting.infodiv.com/audiotube/power_tetrode/power_tetrode0034/kt88-jj2003.jpg)
or are you talking more of some advanced topic I don't yet understand :)
It's my own lack of experience with SE and KT88 that is creating my line of questioning.
Won't know how it truly sounds until I hook it up. And that's gonna be the important part....numbers/schmumbers
-
oh gotcha, so the biasing of the tubes to optimize tone etc?
Very interested in how this goes too. Keep us posted!
~Phil
-
oh gotcha, so the biasing of the tubes to optimize tone etc?
Yeah...or just the use of a huge bottle in a different operating condition than what might be considered "normal"
The SE application is supposed to bring out the second harmonic, and I thought it might be cool to hear that through a KT88...we'll see
The guys pointed out pretty early that it will not be very noticeable if I'm hitting it too hard...so my main goal is basically to get the tonal advantage of the KT88 with approx. the same output as 2 6V6s...I have to try it to know if it's worth it.
The problem that comes with the low B+ is that you have to have a lot of current to get the tube going (for "tone")
Lots of current in an SE build means a big, heavy, expensive OT....and that was contrary to my initial concerns about cost and weight.
Not very sensible when you can have more clean power cheaper with push-pull...so I'll try one stereo side SE and the other side PP...we'll see
-
What do you guys think about the driving stage(s)?...and filling in some of the blanks now that we have some variables resolved?
How should I set up the screens and what value cathode resistor should be a good fit?
I guess I'll need more drive than a parallel AU7? ...how bout 2?
-
Hi SG. :hello:
Colas LeGrippa built a few SE KT88 amps. He LOVED them. Do a search, he posted full schemos.
Last he posted he was working/living in Cuba.
-
Hi SG. :hello:
Colas LeGrippa built a few SE KT88 amps. He LOVED them. Do a search, he posted full schemos.
Last he posted he was working/living in Cuba.
Did an advanced search for posted by: Colas LeGrippa
Keyword : KT88
and only came up with this:
http://el34world.com/Forum/index.php?topic=16733.msg165853#msg165853 (http://el34world.com/Forum/index.php?topic=16733.msg165853#msg165853)
-
> one-electron UBT-2. it's 4.8K at 4/8/16 or 2.4K at 8/16/32
Am I snow-blind or is that a math error?
-
> The problem that comes with the low B+ is that you have to have a lot of current to get the tube going (for "tone")
Not "tone", for POWER.
You want to take a 6550/KT88 up near 40 W Pdiss to get 16W out. (Assume 40% efficiency at 5%-10% THD.)
100V 400mA
200V 200mA
300V 133mA
400V 100mA
500V 80mA
600V 66mA
1000V 40mA
You can get power at low current, just use insane voltage.
I don't think voltage (or current), per se, actually gives "tone". When we hear different tone at different voltages, we are often not changing the current or the load as we should. If the V/I/Load are off-optimum, of cource the overload "tone" will change.
The Optimum Load will be roughly V/I:
100V 400mA 250r
200V 200mA 1K
300V 133mA 2,225r
400V 100mA 4K
500V 80mA 6.2K
600V 66mA 9K
1000V 40mA 25k
> Lots of current in an SE build means a big, heavy, expensive OT
An optimized transformer "scales". For a given Pdiss, various volt/amps, use the same core (and gap), adjust the number of primary turns.
Your problem is that the Likely Suspects don't do this. Hammond gives you one primary winding, with a chart for several nominal impedances. Taken literally, 125ESE can only do 80mA. Looking above, that means 500V supply. But the 6.2K Optimum Load isn't on Hammond's chart. I worked 450V 78mA 35Wdiss and nominal 5K, came shy of 35W*40%= 14W out.
Impedances below ~~~2K, you won't find a single tube to pull well.
Impedances much over 5K, you won't get hi-fi bandwidth without costly fancy winding (even then is tough).
-
> one-electron UBT-2. it's 4.8K at 4/8/16 or 2.4K at 8/16/32
Am I snow-blind or is that a math error?
Lost in translation...and excitement
I'll leave the math police'ing up to you guys
OK....2.4K @ 2/4/8
-
Am I snow-blind
snow here also, but I think He mentioned a *mis-match* spkr to solve that.
might be cool to hear that through a KT88
My gigging son likes the SE KT, says it's chime-y, smooth, loves pedels
You're probably gonna want about 50Vac -p-p available for drive. I was biased about 20-23v, my drive
was about 56Vac p-p, which just started to *bend* the KT when it was dimed. Don't know your pre preference's but the CF TS after the pre sounded best in my world over the *fender* style, fwiw
-
The Optimum Load will be roughly V/I:
100V 400mA 250r
200V 200mA 1K
300V 133mA 2,225r
400V 100mA 4K
500V 80mA 6.2K
600V 66mA 9K
1000V 40mA 25k
Thanks for all of that PRR, but I especially wanted to point this out...
I knew the current to voltage relation,,,but never tied in the impedance as it relates to that equation.
Seeing it listed like that made a couple dormant brain cells perk up...ah-ha moment
-
Haha! I knew I could pull you to the dark side!
Jim :icon_biggrin:
-
Did an advanced search for posted by: Colas LeGrippa
Keyword : KT88
Maybe it was 6550? :think1:
-
Haha! I knew I could pull you to the dark side!
Jim :icon_biggrin:
This guy got me with this one line..."if you were a real man......blah,blah.........KT88"
We'll I knew I'd never build a Major, so before these things collect too much dust, here we are.
You better be right Kemo-sabee
-
> one-electron UBT-2. it's 4.8K at 4/8/16 or 2.4K at 8/16/32
Am I snow-blind or is that a math error?
yes. brain fart. 2/4/8
@$!#×@&!!
-pete
-
Don't know your pre preference's but the CF TS after the pre sounded best in my world over the *fender* style, fwiw
Thanks shooter...
Just a power amp driver circuit needed..no tonestack (see partial schemo above)
I never measured the preamp for it's output signal voltage, but I'm assuming I'm gonna want to set this up to keep a big signal pretty clean and just get it to the grid of that KT as simply as possible.
-
MAX idle current through UBT-2 is 120mA - use caution!
How about a 1/8 amp FA fuse in line between plate and OT on the breadboard?
So, I should be right there on the edge @120mA @ idle(looking at PRR's chart)?...slightly lower than the 133mA he's got for 300VDC
With these PTs I am seeing approx. 315VDC plate to K at idle with just the 6V6 in there.
So cathode resistor value will be critical.
Now I see where/how the voltage/current/impedance conundrum comes into play, and I see why any logically thinking mammal would shy away from this application.
-
So cathode resistor value will be critical.
I'll give it a shot...based on ballpark #s
Lets say 120mA total plate plus screen current
Made up bias voltage of -30VDC (based off shooter's # of 56V p-p)
30 / .120 = 250ohm R-K
Any good?
-
Haha! I knew I could pull you to the dark side!
Jim :icon_biggrin:
This guy got me with this one line..."if you were a real man......blah,blah.........KT88"
We'll I knew I'd never build a Major, so before these things collect too much dust, here we are.
You better be right Kemo-sabee
Late to the party but better late than never there at all! My head is spinning at all the suggestions and had to stop reading before reaching the end of page 1...so where the heck are things currently?
-
start with 220R-250R for Rk. Vk should be around 25V with 325V, assuming Vg2 is near plate V.
--pete
-
30 / .120 = 250ohm R-K Any good?
You should be close enough, my B+ was tad higher, 360ish, Rk, I think was 270, down from 300, or 300 up from 270 :dontknow:. No notes on final I, used a 3k OT, I'm still pis-poor at final docs
-
Late to the party but better late than never there at all! My head is spinning at all the suggestions and had to stop reading before reaching the end of page 1...so where the heck are things currently?
Good to see you jojo....here we are in a nutshell
- was thinking about a stereo SE EL34 power amp rackmount style build for SE tone (harmonic content) at a reasonable volume
- originally was thinking about weight issues and cost issues and wanted to rule out specific toroidal xfmrs and OTs for current concerns
- got great advice and opinions from people I respect....listened intently
- realized that I should just try 2 small power amps in conjunction with 2- 1x12" speaker cabs for a live wet/dry rig
- went back and forth about stage volume and headroom vs. drummer in small/med club settings
- thought of trying one SE power amp for one side (wet or dry) and one PP for the other
- Jimbo pushed me towards the KT88 through PM by attacking my manhood
- realized that I should just try a SE KT88 to cross it off the bucket list and hope it fits the bill for either the wet or dry side of the rig (because I have a pair here)
- was (and still am) being taught how to properly 'design' it
- DL hooked me up with a very nice OT
- will put the circuit on the breadboard as soon as the OT arrives and then try to work backwards through the drive stage(s)
- may try to manipulate final output with speaker selection...i.e. SE dry side through high efficiency speaker to compete with PP wet side through low efficiency speaker (or opposite)...may use VVR on PP side to balance volume
- will use 2 of Dougs stout chassis because they mate up well with my 'thiele' type cab dimensions (and because I already have one here)
- will worry about PP side later....thinking either EL34 or 6L6 into Hammond 1760L (because it's here)
- we had to discuss concerns about 340V B+ and the current / impedance demands on the OT for KT88 for any kind of sensible operation. (because I have PTs in stock with 240VAC secondaries)
....besides me flip flopping a couple times, that's about it
-
Thanks for the info., with so many ideas and suggestions it's hard to know which direction you're going. I agree with PRR's tone assessments above (big shocker here) and without reading it prior to my own gut instincts, was immediately thinking of a higher B+ with less current KT88 situation. You can use the OT you & DL listed but in reverse mis-match to get up to near the optimum load but isn't necessary to get it perfect. Which would be the range of ~9K @ 8/16/32 option for the windings. I tend to like pushing towards the smaller side of the plate loading listed match in general. Smaller current = smaller size, weight, & core, etc. with power rating of 20w should be fine. (didn't read ratings for OT you are thinking of using).
I was thinking of using only the 240vac outside windings (no CT use) 240-240 > FWB > ~600-620Vdc loaded on plate & screen while using VVR would be fun. Big tubes like big voltage (just ask Jimbo) but with VVR you can tailor whenever wanted and the nice thing especially SE when you dial it down a tad you will notice the floor noise hiss drop as well. It's a small issue in a small gig/bar scene but more valued if ever recording or simply practicing at home. I think you should VVR only the KT88 if you decide to incorporate it. I changed the PT for a slightly higher voltage & current rated one after this schematic was made but it didn't make any tonal difference other than running cooler (one of my original goals on that amp was also seeing how close I could design that amp to the edge of various parameters successfully).
http://el34world.com/Forum/index.php?topic=10769.msg99089#msg99089 (http://el34world.com/Forum/index.php?topic=10769.msg99089#msg99089)
I ran my preamp V1 tube to bias two stages simultaneously in three ways and helps with a nice variety of tones & gain levels to suit your mood or a minimum of two at least on a DPDT On/On switch. I then also made a tone stack bypass mod for another given a big signal boost and tweed feel. I suggest doing something similar to provide various flavorful options to the mix and you'll have a nice fun versatile amp there.
http://el34world.com/Forum/index.php?topic=9954.msg125523#msg125523 (http://el34world.com/Forum/index.php?topic=9954.msg125523#msg125523)
"....besides me flip flopping a couple times, that's about it"
That's fine unless you're a certain female running for president?
-
Ciao SILVERGUN
Here is my provocation
Mesa Boogie 20/20™ Stereo Power Amplifier
http://mesaboogie.com/support/out-of-production/2020.html (http://mesaboogie.com/support/out-of-production/2020.html)
http://mesaboogie.com/media/User%20Manuals/20-20%20Manual.pdf (http://mesaboogie.com/media/User%20Manuals/20-20%20Manual.pdf)
(http://i76.photobucket.com/albums/j21/triaxtasy/20-20.jpg)
(http://i76.photobucket.com/albums/j21/triaxtasy/2020PWRsup.jpg)
(http://i76.photobucket.com/albums/j21/triaxtasy/IMGP0302.jpg)
Based on the original idea to fit all in a head space and in a power of 20 + 20 W (however not very much nor very low)
Franco
-
The problem that comes with the low B+ is that you have to have a lot of current to get the tube going (for "tone")Lots of current in an SE build means a big, heavy, expensive OT....and that was contrary to my initial concerns about cost and weight. Not very sensible when you can have more clean power cheaper with push-pull...so I'll try one stereo side SE and the other side PP...we'll see
Yes, that well summarizes the issue of big iron SE, especially if there's 2 of them.
Another thought. Do you really want power tube overdrive? This is not an easy question for your application. KOC says power tube overdrive is unnecessary & wasteful, because you can get any tone you want in a preamp. The power amp need only supply a clean boost to drive loudspeakers. The clean power amp can boost overdrive tone created earlier in the preamp. With your Triaxis preamp you probably don't need power tube overdrive to get your desired tone. But if you want the option, you may find the amp too loud for the venue. Some alternatives: overdrive only 1 SE amp & keep the other clean; install a triode SW or use Tubenit's switchable cathode resistor-cap circuits to cut power for less headroom & earlier overdrive.
-
or use Tubenit's switchable cathode resistor-cap circuits to cut power for less headroom & earlier overdrive.
VVR does a nice job for this by lowering PT's voltage while it's grid gets hit normally since it gets much more sensitive (lowers power tube headroom considerably) running at lower voltages. It also preserves normal high end and harmonic content from being diminished which resistance normally affects.
-
Another thought. Do you really want power tube overdrive?
YES!!!!! I'm not sure about SE, but there is nothing that sounds as sweet as whipping KT88's in PP. Preamp shmeamp... :icon_biggrin:
Jim
-
Yeah, I'm with you; but for Arena Rock! :m4 :m9 :m6 :guitar1 :m19 :m16 :m12
SG wants this rig for local bars :m11
-
No, I'm sayin that if the KT88 sounds as good flogged SE as it does PP, I think he will be very happy! :m15 Sorry, didnt esplain meself very well... :BangHead:
Jim
ps Preamp shmeamp :icon_biggrin:
-
if the KT88 sounds as good flogged SE as it does PP
It's lots harder to flog the 88 in SE mode, but if you do, and have no NFB, expect some mean n ugly replies :icon_biggrin:
-
OT got here on Monday, but I've been tied up all week with BS...sorry if I didn't address all above posts, but I do appreciate all of the input.
Big THANKS again to DL for his kind gesture, incredibly fast shipping, design help, and all around good dude-ness...I even got a special surprise in the box!
I know how much you guys like big words and pretty pictures, sooo....
There it is! put the 9V in there for scale
-
Ooooooooooo!!!! Ahhhhhhhhhh!!!! Cant wait to hear the results!
Jim
-
Also wanted to give my .02 on cabinet(s) for this build. You mentioned 2, 1x12 cabs. I'm sure that will work fine and may be the best for portability. However, I did want to throw this out to you. I have a 4x12 that can be split for stereo. I tried it with my Scholz/Rockman setup which is basically the modules running into a 150 watt/channel SS PA. The sound was great, just a glorious swirl in a small package. (The response was horrid because to get the true Boston vib, you need full range speaks) I'm not suggesting that you build a 4x12, but a 2x12 with a mono and stereo jack might be more useful onstage and with other builds? Separation (as in two cabinets spaced out) is great, but if it's miced, it will not matter. Remember the angled 2x12 cabinet with ports that I posted a couple of years ago on that speaker thread? That design might be just the ticket.
Jimbob
-
Big THANKS again to DL for his kind gesture, incredibly fast shipping, design help, and all around good dude-ness...I even got a special surprise in the box!
Yeah, he's like that. A lot of people from Texas are. Always a surprise in the box. He sent me some rocker switches recently. Used about 50 FWB rectifiers as packing material! :huh:
-
SG - Aren't you glad you have that glorious test rig set up paying off for you once again? Watch out for that Ritchie guy's advice next thing you know he'll have you label the input jack "No Tele's" :laugh:
-
SG you're welcome.use it for pp amp of other. it drove 4 x el84 in pp with 8 ohm load in a baldwin organ.
sluckey i was goung to send more but ran out of room... :p
no tele input jack - i like it!! ;-)
thanks for the kind words... y'all !
--pete
-
Wait a minute, are you working with outer space beings with their technology? :w2:
(Dang it, mine won't enlarge, look at reply #79 and you'll see the critter.)
-
I see it too! There's some sort of plate-being or getter-guard in there? Definitely appears to be lacking sunshine either way?
-
I see it too! There's some sort of plate-being or getter-guard in there? Definitely appears to be lacking sunshine either way?
:laugh: Well I guess stranger things have happened in Philly? I mean just look at their baseball mascot. :think1:
-
SG - Aren't you glad you have that glorious test rig set up paying off for you once again?
Yes indeed...it took all of about 30 minutes to get it cooking..priceless
I wound up putting a 12AT7 at the input just to push the AU7 driver enough to get a big signal in...my signal gen. only puts out about 1.5V max
Here's some #'s
No load B+ = 357VDC
Idle:
plate - K = 265VDC
25VDC across 250R K
95mA
25W pdiss
Loaded clean output @ approx.7 watts before going square pretty quickly...
But that's a VERY loud 7 watts, and square doesn't sound so bad either
I hooked up that little Deluxe Champ Reverb through a load - line level box and ran it into the input and it sounded pretty big for a little SE 7 watter
All, preliminary fun, but I figure I'd better report something after teasing you guys with that pic
Wait a minute, are you working with outer space beings with their technology? :w2:
Are you talking about MY reflection?...yeah I need to get out more
-
Are you talking about MY reflection?...yeah I need to get out more.
Conspiracy cover up! :laugh:
Tryin to keep all the good outer space secrets to yourself. :undecided:
-
before going square pretty quickly
just the output of the 88?, or were you driving it squared?
-
before going square pretty quickly
just the output of the 88?, or were you driving it squared?
The KT plate signal went square well before the signal at the grid.
Makes. sense right?..with that stupid low B+
-
The KT plate signal went square well before the signal at the grid.
Makes. sense right?..with that stupid low B+
That's why I was trying to coerce you to drop the CT and wire up both outer ends of that PT to a FWB config and get those volts up??? Any chance you might give it a go? Of course you'll have to drop the preamp back down after the screen node.
-
PT seems marginal for application. 62V drop w/ cap loaded FWB.
--pete
-
The KT plate signal went square well before the signal at the grid.
Makes. sense right?..with that stupid low B+
That's why I was trying to coerce you to drop the CT and wire up both outer ends of that PT to a FWB config and get those volts up??? Any chance you might give it a go? Of course you'll have to drop the preamp back down after the screen node.
No CT on this xfmr...it's basically just a 120v to 240v isolation transformer with what I thought was a very impressive 570mA rating
PT seems marginal for application. 62V drop w/ cap loaded FWB.
Yeah, I don't get it...I'll post the spec sheet tomorrow and you can correct my thinking...
Good thing I ain't married to it. Didn't think it was gonna dump it's guts like that.
-
seem like a 135VA transformer should have better regulation than that with
170-180mA AC load. sorry that's .62 * .1A
http://www.hammondmfg.com/pdf/5c007.pdf (http://www.hammondmfg.com/pdf/5c007.pdf)
--pete
-
Here it is:
https://www.hammfg.com/files/parts/pdf/185F230.pdf (https://www.hammfg.com/files/parts/pdf/185F230.pdf)
I got a deal on some of these and used them on a few small amps...still have a couple left, which is why I was trying to use it
-
so, ya say ya have two of those PT?
try this (see attached), it's a stacked FWB. wire it up carefully as depicted. no tolerances for error. bad wire job = bad juju mon: it leaks magic smoke. lots of it. bring it up connected to a lamp limiter.
makes 485V or thereabouts. screen supply should be around 325V. preamp stages are set to something less than 480 if tap the plate power rail or less than 325V if you tap the screen power rail. i chose the screen power rail in this scheme. throwing darts i'd say around -30V to -32V at Vg1 for 40W Pdiss at 450Va-k you need around 90mA Ik. so 30V/90mA 350 ohm Rk. start at 430R and work down. Rk should be 5-6W: 10W would be better.
works on SIM so should work for you. CAUTION! unloaded B+ at the plate power rail can potentially be over 500V, so me mindful of cap voltage ratings. for this PS, 350V radial cans are low-cost and should work well.
--pete
-
Makes. sense right?..
I guess, my plate was about 100 more than yours, and fwiw, I used EL34, 6550 and KT88, the 88 sucked B+ down the most
-
Alright DL, that'll take a little finagling
Going forward, what do you think about https://www.hammfg.com/files/parts/pdf/290EX.pdf (https://www.hammfg.com/files/parts/pdf/290EX.pdf)
I think I can hog out the stout chassis hole and fit this on there
Makes. sense right?..
I guess, my plate was about 100 more than yours, and fwiw, I used EL34, 6550 and KT88, the 88 sucked B+ down the most
I'll probably run some numbers with EL34 in there before I'm done experimentin'...and before I smoke anything
-
Haha! I knew I could pull you to the dark side!
Jim :icon_biggrin:
I saw the visual representation of the dark side last night.
I measured clean output and then proceeded to measure fully square output at around 10 watts.
But there was a point (around "11") where the tops of that square wave started to get a PITCHFORK shape to it, and that's where things got real nasty...
Not sure if I'll ever want to go back there again....kinda scary
-
Not sure if I'll ever want to go back there again....kinda scary
LOL, nice :)
:l2:
~Phil
-
B+ @ 276mA is way more than you need.
-
that's where things got real nasty...
Most all my builds are PSE and you're right, without NFB, (even with), you sometimes wind up in the
death-metal, Satans on His way sound :icon_biggrin:
-
B+ @ 276mA is way more than you need.
Ahh, right...especially since as my B+ goes up my current requirement comes down.
I got a little over zealous after watching that other PT get dragged down, but I do always err on the side of too much current capacity..
And I liked the EX cause it doesn't have a 5V winding
-
And I liked the EX cause it doesn't have a 5V winding.
You could use a 5acv wind for relay's if needed. (If the rectified dcv is a little low/on the edge, they make 2.5v relays.)
-
Now there's a double tranny schematic I've never seen before. Now I know why pete's got all those rectifiers? :icon_biggrin: It seems disconcerting to see the neg point on top bridge rect going to the lower winding like that but in series things like that happen? Now if this gets SG that higher voltage I've been wanting to see then a big :thumbsup: you go boys! SG - get it goin'! Too bad you just don't have a 400-0-400 PT though... wait just a second; would not this work perfectly? - http://www.ebay.com/itm/STANCOR-12558-1-POWER-TRANSFORMER-TUBE-AMP-12AX7-6L6-6V6-5Y3-12AU7-5E3-/321991180693?hash=item4af82b8195:g:UDwAAOSwEK9T9P2z (http://www.ebay.com/itm/STANCOR-12558-1-POWER-TRANSFORMER-TUBE-AMP-12AX7-6L6-6V6-5Y3-12AU7-5E3-/321991180693?hash=item4af82b8195:g:UDwAAOSwEK9T9P2z)
-
Now there's a double tranny schematic I've never seen before. Now I know why pete's got all those rectifiers? :icon_biggrin: It seems disconcerting to see the neg point on top bridge rect going to the lower winding like that but in series things like that happen? Now if this gets SG that higher voltage I've been wanting to see then a big :thumbsup: you go boys! SG - get it goin'! Too bad you just don't have a 400-0-400 PT though... wait just a second; would not this work perfectly? - http://www.ebay.com/itm/STANCOR-12558-1-POWER-TRANSFORMER-TUBE-AMP-12AX7-6L6-6V6-5Y3-12AU7-5E3-/321991180693?hash=item4af82b8195:g:UDwAAOSwEK9T9P2z (http://www.ebay.com/itm/STANCOR-12558-1-POWER-TRANSFORMER-TUBE-AMP-12AX7-6L6-6V6-5Y3-12AU7-5E3-/321991180693?hash=item4af82b8195:g:UDwAAOSwEK9T9P2z)
That looks good jojo..but also sold (?)
I don't really have a voltage shortage issue here as I can easily tap more off of my bench supply...only problem with that is it doesn't accurately show me how a real xfmr is going to perform.
I 'could' hookup per DL's schematic, but even that doesn't get me to a real world solution.
It might make sense for me to transfer the circuit to my bigger board and have unlimited control. This small board is somewhat limited...I realize now that I should have made another power pigtail so my bench supply could easily feed either board....considering that also, and should probably just do that since this will surely come up again.
-
Alright DL, that'll take a little finagling
Going forward, what do you think about https://www.hammfg.com/files/parts/pdf/290EX.pdf (https://www.hammfg.com/files/parts/pdf/290EX.pdf)
I think I can hog out the stout chassis hole and fit this on there
Makes. sense right?..
I guess, my plate was about 100 more than yours, and fwiw, I used EL34, 6550 and KT88, the 88 sucked B+ down the most
I'll probably run some numbers with EL34 in there before I'm done experimentin'...and before I smoke anything
this one (http://www.mojotone.com/transformers/Fender/Power/MT-FENDER-MOJO758.pdf) drops right in the v2 stout chassis. 112 bux from mr. hoffman. it's pretty stiff and the one i used to proof the mini plexi w/ dual EL34 SE. the hammond 290CX (http://www.mouser.com/ds/2/177/EDB290CX-747282.pdf) will work as well. i published a list of PT that would fit in the stout v2 chassis. click here (http://el34world.com/Forum/index.php?topic=18270.msg186417#msg186417) for a list of PTs that should fit, or will fit with minor enlarging.
--pete
-
Now there's a double tranny schematic I've never seen before. Now I know why pete's got all those rectifiers? :icon_biggrin: It seems disconcerting to see the neg point on top bridge rect going to the lower winding like that but in series things like that happen? Now if this gets SG that higher voltage I've been wanting to see then a big :thumbsup: you go boys! SG - get it goin'! Too bad you just don't have a 400-0-400 PT though... wait just a second; would not this work perfectly? - http://www.ebay.com/itm/STANCOR-12558-1-POWER-TRANSFORMER-TUBE-AMP-12AX7-6L6-6V6-5Y3-12AU7-5E3-/321991180693?hash=item4af82b8195:g:UDwAAOSwEK9T9P2z (http://www.ebay.com/itm/STANCOR-12558-1-POWER-TRANSFORMER-TUBE-AMP-12AX7-6L6-6V6-5Y3-12AU7-5E3-/321991180693?hash=item4af82b8195:g:UDwAAOSwEK9T9P2z)
That looks good jojo..but also sold (?)
Did you change your cell number? I've texted you several times...
-
Now there's a double tranny schematic I've never seen before. Now I know why pete's got all those rectifiers? :icon_biggrin: It seems disconcerting to see the neg point on top bridge rect going to the lower winding like that but in series things like that happen? Now if this gets SG that higher voltage I've been wanting to see then a big :thumbsup: you go boys! SG - get it goin'! Too bad you just don't have a 400-0-400 PT though... wait just a second; would not this work perfectly? - http://www.ebay.com/itm/STANCOR-12558-1-POWER-TRANSFORMER-TUBE-AMP-12AX7-6L6-6V6-5Y3-12AU7-5E3-/321991180693?hash=item4af82b8195:g:UDwAAOSwEK9T9P2z (http://www.ebay.com/itm/STANCOR-12558-1-POWER-TRANSFORMER-TUBE-AMP-12AX7-6L6-6V6-5Y3-12AU7-5E3-/321991180693?hash=item4af82b8195:g:UDwAAOSwEK9T9P2z)
That looks good jojo..but also sold (?)
Did you change your cell number? I've texted you several times...
somebody bought it... hopefully one of you two characters.
--pete
-
somebody bought it... hopefully one of you two characters.
--pete
why what gives you that idea? :angel
-
somebody bought it... hopefully one of you two characters.
--pete
why what gives you that idea? :angel
imma clairvoyant texican! :icon_biggrin: no, not really, just WAG...
--pete
-
I like the first one :icon_biggrin:
So I figure around 525 B+ loaded? That should get there for Vp but looking at datasheets they show Vg2 about 300v - why? Why not just below Vp say 500-ish then drop down for preamp voltages? Especially if I use VVR only on the 88?
Re-thinking again :think1: - that's likely because of hi-fi BS specs in wanting a pristine pure sign wave...
-
Haha! I knew I could pull you to the dark side!
Jim :icon_biggrin:
I saw the visual representation of the dark side last night.
I measured clean output and then proceeded to measure fully square output at around 10 watts.
But there was a point (around "11") where the tops of that square wave started to get a PITCHFORK shape to it, and that's where things got real nasty...
Not sure if I'll ever want to go back there again....kinda scary
If it looked like this, I'd say you were on the right track! :icon_biggrin:
Jim
-
If it looked like this
When I see that, I hear gnashing of teeth :icon_biggrin:
-
revised stacked FWB. this rev., 1a, has less ripple at C1. connect top bridge (-) to lower bridge (+). see attached for clarification.
--pete
-
I like the looks of this one better but wouldn't balancing resistors be wanted?
-
The bridges put out different B+ voltages so you don't want to try and force them to be the same with balancing resistors.
-
Good point on that. Okay, the big unanswered question I have is about the KT88's screens...I've seen a number of designs that allow the plates to go well into the 500 volts area but why do the screens need to be kept so low at around 300v??? Most other tubes use a 1k resistor which allows them to be not far under the plate voltages. What is the big deal about KT88s screens?
-
I went back and tried to find anything that might have been skewing those #s and found a couple loose screws in power rail, so I ran numbers again with everything all tight. Included screen current measurements for jojo. EL34 does not have the same pitchfork effect on the wave before going square (make your own conclusion)
KT88
280VDC a-k
23V across 250 ohm
87mA @ 24W pdiss
approx. 8W clean out - 10W square
Screen current: (measured across 1K screen resistor)
5mA clean
17mA at fully square max output
EL34 under same conditions:
303VDC a-k
17V across 250ohm
65mA @ 20W pdiss
approx. 6W clean output up to 8W fully square
Screen current:
10mA clean
16mA at fully square max output
-
Tapped into bench supply and got plate voltage up for more testing...also did some play/ear testing and seemed to prefer the 88 (at either voltage)
Not very scientific but, something.
For anyone keeping score, I had also left the primary load at 2.4K (accidently) for this set of testing. I'm assuming that I should have gotten rid of the mismatch and returned the pri to it's spec'd 4.8K for 'best' results.
KT88
362VDC a-k
31V across 250ohm
118mA @ 43W pdiss
approx. 12W clean up to 16W full
Screen current:
12mA clean
26mA full
EL34
392 a-k
22V across 250ohm
84mA @ 33W pdiss
approx. 9W clean up to 11W full
Screen current:
12mA clean
22mA full
-
Last but not least, change load back to 4.8K into 8 ohms...raised input voltage again
KT88
411V a-k
37V across 330ohms
107mA @ 44Wpdiss
approx. 19W fully square
ran out of room on scope to judge/guesstimate clean
Screen current:
30mA at full clip
-
Okay, the big unanswered question I have is about the KT88's screens...I've seen a number of designs that allow the plates to go well into the 500 volts area but why do the screens need to be kept so low at around 300v??? Most other tubes use a 1k resistor which allows them to be not far under the plate voltages. What is the big deal about KT88s screens?
I would tell you (again), but I would have to kill you. There is no violence allowed on the forum. Sorry!
Jim :icon_biggrin:
-
Please correct me if I'm wrong... We want the screens low to limit dissipation when the plate swings lower than the screen volts on max signal flogging - which is very important in Class A? Since we are close to max safe dissipation all the time anyway? Gotta keep those screens warm, but not glowing! :dontknow:
Jim
-
Take plate voltage up. Current must go down to stay inside Pdiss.
The peak current for audio will be about twice the average (idle) current).
Screen voltage determines maximum plate current.
So as plate voltage goes up, screen voltage "can" go down.
Lower screen voltage allows smaller G1 bias and signal voltage, easier drive.
Lower screen voltage indirectly affects the knee voltage. The effect is not large, but you want the lowest knee voltage for best plate voltage swing, so why over-volt the screen more than needed for the current you need.
OTOH.... a low screen voltage is awkward. Screen current is uncertain and changes a lot, so it needs to be a fairly solid supply, not a dropping resistor. For *this* reason, audio designers favor picking tubes and supply voltages so that screen can eat nearly plate voltage. And for historical reasons, most "audio" pentodes can work very happy at 250V to 350V supply for P and G2.
-
play/ear testing and seemed to prefer the 88
same conclusion I came to, fwiw
-
Good point on that. Okay, the big unanswered question I have is about the KT88's screens...I've seen a number of designs that allow the plates to go well into the 500 volts area but why do the screens need to be kept so low at around 300v??? Most other tubes use a 1k resistor which allows them to be not far under the plate voltages. What is the big deal about KT88s screens?
KT-88's were developed for hi-fi to be used in ultra-linear for hi power w/ lo distortion, or in triode mode. Checkout this article: http://education.lenardaudio.com/en/14_valve_amps_4.html (http://education.lenardaudio.com/en/14_valve_amps_4.html) But they don't have to be used that way.
-
KT-88's were developed for hi-fi to be used in ultra-linear for hi power w/ lo distortion... But they don't have to be used that way.
Exactly! (...what's happening???)
-
The KT88 was marketed for audio (few hi-fi ran to 50W-100W sizes).
It specifically says "similar to 6550", which is well documented as an Ampex motor servo driver.
It isn't really designed-for ultra-linear. But in the late 1950s, UL was all the rage, every new tube-sheet had to show UL conditions.
The EL34 really lucked-out because it came on the cusp of the UL craze, and its heavy G2 current (normally bad) was turned by UL into a minor advantage. The '34 is a re-pack of a loooong line of low-price larger power pentodes (to pre-WWII EL3).
8417 and 7591 (and a few others) were specifically re-designed (from 6550 and 6L6) at the request of the hi-fi makers (8417 is all Fisher's fault). 7189 is re-rated EL84, an old car-radio tube.
-
:bump1:
Colas, have you seen this thread?
(He was on line, but I guess I bumped this too late?)
-
OK, I'm onto something here..
Play testing tonight with the Triaxis into the '88 Tone Blaster' power amp and really just couldn't be more delighted with the tones.
I was previously left with the impression that the Triaxis wasn't quite right and it was somehow contributing to my questionable tone choices of the past...it appears now that I was dead wrong and it was an OPERATOR ERROR. I think I just always pictured this big scary issue that was going on between the pre and power amps and it was just a big tone suck hole and there was nothing I could do about it (this was 15 -20 years ago when I still believed in Santa).
I don't know what was wrong before, but now that I have this power amp and the ability to set the volume of the preamp and drive the 88 as hard as I want, I have found a huge vat of the special sauce that I came here for initially.
Big, round, honking, clear, fat, tight, elastic, punchy, singing, sweetness!
I figured out just how much drive I wanted by trial and error and going back and forth with driving stage changes. I settled for an AU7 input tube into a paralleled AU7 driver, and it don't matter what the numbers say because it just plain ole sounds frackin' perfect.
The preamp has an output control, the power amp has both an input volume and output volume control. And it's in the interaction of those level controls where I was able to find my center, and now I can go forward......
Just thought that was worthy of an update, because at one point I thought to myself 'that's the sound/control I've been looking for right there!'
I'll be working on a postable schematic, but there's really nothing to it....this has more to do with the interaction of the preamp volume and being able to drive the output at will...brought out such a greater presence and body in the sound. The preamp has a lot to do with it, but my glory has been found in the interaction of the two.
THANKS AGAIN GUYS!!
Without all of you're input, experiences, opinions and shipping prowess,,I never could have made it here this quick or accurately.
.. and I'm very happy to report that one KT88 can be and is enough for 'this' specific application. (considering that I will have a whole other power amp running the wet side)
Oh yeah, that's right,,,I still have to build 'em.
For the record @idle:
373VDC a-k
350 g2-k
33V across 330ohm
95mA @ 35 pdiss
-
Hey, that is great news! :icon_biggrin:
Thanks for posting your findings SG! :icon_biggrin:
-
I settled for an AU7 input tube
I to have been using AU in the V1 spot for the last 3 builds!
when you get a chance, run it through a good 4X cab just for fun :icon_biggrin:
when you really go off the deep end, look into the iron required for a PSE KT88 :think1:
-
At first I tried it with just the parallel AU7 barely pushing the 88. It sounded good but kinda sterile, lifeless, and just polite.
The breakthrough came when I added the single AU7 input stage and it wound up driving the driving stage and that just did wonders. Fully cranked it's slightly over the edge, but rolled back just a hair and the response is just incredible. I feel like I got lucky because I got it to the edge and then worked it back from there without losing the magic.
-
Nice to see you've found your happy place SG. I've done a bit of research on the 88's g2 and from what I glean there is a supposed sweet spot at appx 250v. And this is for guitar not hifi use. But It's not good enough to simply feed just any voltage this way using a dropping resistor, rather it is supposed to be regulated at this voltage and/or possibly up to 300v or so? This was found using VVR in the same way as PRR suggested to another member wanting to control his el84 screens in another thread. I've heard also that g2 ran too low caused the 88 to turn darker... Just some more food for thought for you in case you feel like experimenting any further?
Questions, And what did you get if you tried an ax or ay there?
But, now you realize you have sold your soul to the (kt88) devil right? Jimbo will not let you forget or live this down - unless you've accomplished this all with strictly only a tele? :laugh:
-
Questions, And what did you get if you tried an ax or ay there?
Too much gain, and clipping...for what i could tell
I had it set up with an input 12AT7 into parallel 12AU7 and it was way too much drive
But, now you realize you have sold your soul to the (kt88) devil right? Jimbo will not let you forget or live this down - unless you've accomplished this all with strictly only a tele? :laugh:
Oh no...now that megalomaniac isn't gonna be able to fit his head through the imaginary gates of the forum...
I can just hear it now... "Hey SG, how do you like that amp I "designed" for you?"
It does have me thinking more about the effect of that 12AU7 driver CF in the Major, and how that might have something to do with his delusional obsession.
Cant wait to finish assembling the Tele so I'll finally have a grown up's guitar to plug in and play some Beatles.
Don't feel like I need to mess with the screens...don't want to limit max output too much.
I have a 4.7K dropper between the plate and screen nodes, and a dedicated 1K screen resistor. I do understand what you're suggesting for a separate screen supply, and might try it before i wrap it up.
-
https://www.youtube.com/watch?v=4WrTZweHXTI (https://www.youtube.com/watch?v=4WrTZweHXTI)
:headbang:
-
send PM if you'd like to buy another UBT-2 to round out as a stereo setup. :icon_biggrin:
--pete
-
send PM if you'd like to buy another UBT-2 to round out as a stereo setup. :icon_biggrin:
--pete
PM coming as soon as I get done rocking out to Sabbath...our secretary came in my office and immediately just turned around and walked right back out. When she got back to her office she came over the intercom and said "what is that?"...I guess anything that deviates from Happy101FM is not work appropriate.
It's amazing what a little tube breakthrough (that no one around you understands) can do for your mood.
I have officially changed the name to "The Smokin' 88" power amp....you watch, he's gonna try to hit me up for royalties.
(or the Silvergun Smokin' 88 as it will appear in my full line catalog next year)
I'm gonna send Jimbo a hat..."Make SG Great Again!" (he's been a huuuuge supporter)
-
:thumbsup:
-
:thumbsup:
You know JJ,,this harkens me back to the Herzog experiment (to which I had a similar reaction of how pushed everything felt), and how enamored I was with that concept...except in this case it makes more sense, and is way less noisy and much more controllable.
The biggest difference here is that the cleans stay clean but just feel more alive and sound fuller....and if you want some slight breakup, you can hit the 88 a little harder, and it works. The OD is just KILLER, and you can really dig in without it mushing out. (I'm pretty sure that 6V6's would be calling for their mommy at this point)
For me, there really is something to having the preamp juiced up pretty good and then knocking some of that down(with the Master preamp out) to be able to "re-amp" it and blast the grids of the output tubes....and have some sort of ultimate control over it, rather than an amp with fixed values in the PI and so-forth..
And without resorting to a PPIMV.....when I reached that sweets spot last night it left a huge grin.
Sometimes I'll get to a place in a build/experiment and I'll think "we'll that sounds acceptable", and I'll just leave it because it conforms to the topology(s) of the past....in this case I'm very glad that I decided to push a little further and drive a driving stage into those KT's....it paid off.
There are a couple fine points to be worked out in the schematic, and I'm working on getting that together with a couple more questions.
I would like to think that I hit an impedance matching sweetspot where the output of the Triaxis is a good match for the input of the Smokin' 88.
The output impedance of the Tri. is 25K
-
For me, there really is something to having the preamp juiced up pretty good and then knocking some of that down(with the Master preamp out) to be able to "re-amp" it and blast the grids of the output tubes....and have some sort of ultimate control over it, rather than an amp with fixed values in the PI and so-forth..
And without resorting to a PPIMV.....when I reached that sweets spot last night it left a huge grin.
...the input of the Smokin' 88.
SG, keep the name simple...Smokin' 88 is perfect (despite a certain person's coercing).
I'm a little confused on your comment regarding that first paragraph in that you're saying you like the Vol control right before the pi (to control the signal amount right before) but then "with the fixed values in the pi"...and "without resorting to PPIMV" -> is confusing without a schematic to understand picture what you're actually doing?
-
I'm a little confused on your comment regarding that first paragraph in that you're saying you like the Vol control right before the pi (to control the signal amount right before) but then "with the fixed values in the pi"...and "without resorting to PPIMV" -> is confusing without a schematic to understand picture what you're actually doing?
Sorry jojo, I was mixing my SE results with PP ideals...I should have never said PI other than to mean a "driving stage" before the power tubes.
What I'm suggesting to take away from this is the idea that we could have more control after the preamp (in a standard SE amp topology)
i.e...So you build a Champ and want to push a 6L6 but those two little gain stages aren't quite whipping the grid of the 6L6 (it sounds OK, but still ho-hum),,,try inserting a volume pot, feeding another gain stage, but preferably an AU7 so we don't add TOO much gain,,,but the AU7 swings the stock Champ preamp into the 6L6 grid and you get a screaming little banshee (or super crisp, rubbery cleans)
I'd like to run with this ball a little after the amps are built and I can just leave the KT on the b-board with the current driving stage in place...my thought would be to try the Deluxe Champ Reverb I built, and instead of running the last stage into the 6V6 (as it currently is), I will "re-amp" it by running it into the driving stage and then to the 88. I have a feeling it's going to be pretty badass.
-
Glad you like the KT-88's. I almost didn't make the suggestion, as you originally had other tubes and trannies in mind.
The output impedance of the Tri. is 25K
Wow, that's high; but if it works maybe OK. For further tinkering. . .
Some thoughts: Buffer pedal; or various fx pedals might be used just for their buffering function between the Triaxis and the power amp; or an acoustic guitar piezo preamp, which expects to see a hi impedance source. This might be a cheap & simple way to see if better impedance matching helps. Or, input matching trannie on the power amp. Or, for those of us who like tubes :occasion14: in his Preamp book, Merlin has a cathode follower input stage designed to accept hi impedance sources. (That seems to make at least 2 of our members who are devout "cathode followers". :icon_biggrin: )
-
I will "re-amp" it by running it into the driving stage
If you're into tinkering, I did an octal *driver* using a 6SN7 driving a quad SE of EL84s power amp.
the 6sn7 added some much needed *butter* to the sound, while still being able to send the quad,
calling for their mommy
:icon_biggrin:
-
To expand (running the risk of babbling):
Most guys will say I want a little more gain out of my amp, and the first thing they do is try to add some gain to the existing triodes by increasing resistor values (...whatever)...or re-bias output tubes, etc.
I'm guilty of this as well, and have in the past, wound up with a muddy mess of too much front end 'gain'
For a (future) PP example:
What if we interrupted the hardwired connection of PI to power amp, and added in a pot controlled AU7 stage on each side of the wave after the PI, to "re-amp" the signal before it gets to the power tubes. So it's a PPIMV with an AU7 'recovery' stage after the pot. Not so much for the purpose of providing a Master volume, but for changing where the gain is applied, and giving us an adjustable 'grid drive' control.
Imagine a simple 5E3 with each side of the inverter feeding an AU7 to drive 2 6L6s...anyone tried it?
That kind of thinking....
-
Wait, I think I over-reacted to the 25K output impedance of the Triaxis. For voltage matching (bridging, actually) the input impedance should be 10X the source impedance. So if the 1st stage grid leak resistor is at least 250K this should be fine.
-
Wait, I think I over-reacted to the 25K output impedance of the Triaxis. For voltage matching (bridging, actually) the input impedance should be 10X the source impedance. So if the 1st stage grid leak resistor is at least 250K this should be fine.
That 25K rating for the Tri. output is the printed spec for a MAX output setting...does that number increase/decrease as I lower the output from MAX to about 50% ?
Here's the output part of the Triaxis circuit...I'll be using the ones circled in red
-
Here it is as it sits,, and will sit for the weekend, cause I wont be around:
-
Wait, I think I over-reacted to the 25K output impedance of the Triaxis. For voltage matching (bridging, actually) the input impedance should be 10X the source impedance. So if the 1st stage grid leak resistor is at least 250K this should be fine.
That 25K rating for the Tri. output is the printed spec for a MAX output setting...does that number increase as I lower the output from MAX to about 50% ?
You're fine, according to this: http://forum.tcelectronic.com/topic/4907/triaxis-tone-vs-output-connection/ (http://forum.tcelectronic.com/topic/4907/triaxis-tone-vs-output-connection/)
Triaxis output impedance is from 0 - 25K. Lower output setting yields lower (not higher) output impedance. At high Triaxis vol, turning down the 250K input pot on the power amp technically will create an impedance mismatch (less than 10 : 1) & drain away hi's and signal strength. But this may be a desirable feature, rather than a bug to be fixed. Since you like the way it sounds, looks like no problem here.
-
Funny....that's where I've been reading up.
Cause I'll be using the Triaxis with a TC G-system so there may be another impedance hurdle to get over to get it right.
There's a guy over there that has taken a lot of the guesswork out of it for me:
http://www.guitaraffair.com/pdfs/g-system-configuration-and-troubleshooting-guide.pdf (http://www.guitaraffair.com/pdfs/g-system-configuration-and-troubleshooting-guide.pdf)
The G-system utilizes a preamp by inserting it via an 'insert send/return' loop
Should go like this for me:
G-system insert send (low-Z) > into Triaxis input (1M) GOOD
Triaxis output (0-25K) > G-system insert return (24K or 34K) NOT SO GOOD
---That is where I might have to use a DI box or buffer to get the Triaxis low-Z enough to play nicely with the insert return on the G-sys
G-system outputs (low-Z) into power amp inputs (250K or higher if needed...maybe just a fixed 270K resistor)
-
SG I am reminded of your experiment with ppicf you did about a year ago when you explain the power tube grid driving stage except for now being single ended it may be slightly different? But in this way close to the same idea?
I dont see a huge problem to overcome in your idea and an au7 is a good tube to use to try. After the pi outputs I'm thinking there may be the need of a voltage divider after the coupling caps? You'll know by the range of the controls once you get things wired up. Then utilize a dual ganged pot to control both sides at the same time just like ppimv going into the au7's grids.
The other trial would be to have a voltage divider prior to the au7's grids and then coupling caps after the au7's plates with the dual ganged pot after the au7?
There's only these two ways to see what's best but I like the first option going on instinct.
-
SG I am reminded of your experiment with ppicf you did about a year ago when you explain the power tube grid driving stage except for now being single ended it may be slightly different? But in this way close to the same idea?
I dont see a huge problem to overcome in your idea and an au7 is a good tube to use to try. After the pi outputs I'm thinking there may be the need of a voltage divider after the coupling caps? You'll know by the range of the controls once you get things wired up. Then utilize a dual ganged pot to control both sides at the same time just like ppimv going into the au7's grids.
The other trial would be to have a voltage divider prior to the au7's grids and then coupling caps after the au7's plates with the dual ganged pot after the au7?
There's only these two ways to see what's best but I like the first option going on instinct.
Yeah jojo...I think there is something there...and I promised Ed I 'd always give up the good stuff.
I'd also like to see what tubenit would think about this....
It requires way less preamp gain to be able to push the output tube grids effectively...and that seems to be where the "TONE" is.
I'm out for the weekend but I'll try to check back when I get a chance....to the mountains,,time for some R+R!
Maybe we'll start another thread with that idea when I get back and if anyone else wants to give it a go, I think it's worth the time...
..and when I'm done here we can move forward with something like that on the breadboard
-
Yeah jojo...I think there is something there...and I promised Ed I 'd always give up the good stuff.
I'd also like to see what tubenit would think about this....
It requires way less preamp gain to be able to push the output tube grids effectively...and that seems to be where the "TONE" is.
I'm out for the weekend but I'll try to check back when I get a chance....to the mountains,,time for some R+R!
Maybe we'll start another thread with that idea when I get back and if anyone else wants to give it a go, I think it's worth the time...
..and when I'm done here we can move forward with something like that on the breadboard
Speaking of tubenit (king of the cathode follower for a while) I was thinking about the possibly of taking the signal out from the cathodes of the au7 as third/fourth options since not a lot gain is required??
-
> according to this: ...output impedance is from 0 - 25K
It computes as 21.4K down to zero. Close enough to rock.
-
OK, one down, one to go...this one is quiet as a church mouse, and I wound up adding a R/C node before the plate node (as per reading all of your posts on other threads)...excellent punch, presence, clarity, and depth....really happy with it!
I feel like I have the perfect amount of drive but I haven't checked the scope yet to see what that looks like.
377V a-k
356V g2-k
33V across 300ohm rk
105mA @ idle
Changed the title of the thread to be a little more accurate...
Waiting on an octal hole cover after deciding that another cap can was a bad idea because it was too close to the 88.
-
Very nice! :icon_biggrin:
Even has a MOTS face plate! :icon_biggrin:
-
Very neat work. Do you have any insulating sleeve on the filament wires?
-
Very Nice! I'm gonna be *tuning* my-(Son's) SE 88 in a week. He wants more sparkle, He says it has plenty of spank :icon_biggrin:
-
Very neat work. Do you have any insulating sleeve on the filament wires?
Thanks!
No insulation.
Bad idea?
-
Only if one of the naked wires touches the chassis. I'd be nervous about that possibility.
-
Only if one of the naked wires touches the chassis. I'd be nervous about that possibility.
Ok,,,I think I'm good.
I went out and tried to press them against the chassis and because they are 18gauge they don't really move.
I could get the one that's floating over the power tube cathode to touch but it would take a good deal of force, and I would be bending it more than taking up slack.
There's about a 1/4" clearance along the run as-is.
Doesn't make me nervous, and I'm easily nervous'd 'cause I watch the carnage of failed electrical components all the time.
-
Very Nice! I'm gonna be *tuning* my-(Son's) SE 88 in a week. He wants more sparkle, He says it has plenty of spank :icon_biggrin:
Cool...did you ever post a schematic?...I'd be interested in seeing it, and seeing what you wind up doing.
Spank is a good adjective. That it has for sure.
-
Probably a non-issue. Good luck. It's just a PT. I can afford that. :icon_biggrin:
-
Probably a non-issue. Good luck. It's just a PT. I can afford that. :icon_biggrin:
That earns my first emoji since coming back off injured reserve.
:undecided:
I'll keep all touchy-feely gremlins from entering the chassis.
One thing I didn't address which will make an easy addition if deemed valuable:
Would you guys put a B+ fuse on the OT like I had on the breadboard, and what approx. value? (I used an 1/8 amp SB)
DL said OT is rated @ 120mA
Does placement matter? between B+ rail and OT or between plate and OT?
-
Wow, that is too cool! :worthy1: I can't wait to hear the soundclips. I see the Mesa KT88 that you bought, what, 5 years ago! :laugh: Your a good man to finally cross over! If I could make a suggestion for the eventual cabinet? With the name and the KT88 front and center....there HAS to be some sort of cutout showing the master tube in all it's glory!
Oh wait.....those fender knobs gotta go..... I think this deserves some custom aluminum lathe spun knobs that would do this build justice!
Now about the royalties.... :evil5:
Jim
-
Now about the royalties.... :evil5:
Oh, I changed the name again....sorry
It's now the Smoking 88
...totally original and necessary so no one will associate me with "the dark side"
If I could make a suggestion for the eventual cabinet? With the name and the KT88 front and center....there HAS to be some sort of cutout showing the master tube in all it's glory!
That's the plan...I was thinking about glass, and I wanted to look into some heat resistant plexi
I like how Doug's chassis put the tubes across the front like that, so yeah, that's gonna happen
How's these knobs? I bought about 200 of them when Radio Shack was closing...they were in a big bag and all plastic bag components were 95% off....I left with a bunch of different plastic bags
-
did you ever post a schematic
here's the old link with schematic, but it's been modified WITHOUT re-documenting, still a short-coming :think1:
I like your new knobs, I got the same deal :icon_biggrin:
http://el34world.com/Forum/index.php?topic=18394.msg187753#msg187753 (http://el34world.com/Forum/index.php?topic=18394.msg187753#msg187753)
-
....but it's been modified WITHOUT re-documenting, still a short-coming
I do the same thing...I skipped about 4-5 amps because I just couldn't keep up with the documentation.
Sorry I missed that thread...bad timing
It's never too late to reopen it (as others have recently proven)...I think there's interest in how it gets sorted out.
I also enjoyed the nonchalant mention in the opening post...nice to know that I have a similar effect on others that they have had on me.
Your comment about drive signal (56Vp-p) really got me thinking early in this thread and at some point during this process I realized how important it is to REALLY drive the grid of this monster...and then I realized that I was gonna have to give myself a little more headroom with higher B+
This thing pulls B+ down in a big way....unloaded I'm around 460VDC(ish)
-
This thing pulls B+ down in a big way....unloaded I'm around 460VDC(ish)
This is what I figured and why the earlier suggestions of getting that B+ up the higher 400s.
What did you end up doing about the driving tube situation?
I think you should name the thread "Stereo SE KT88 amps for live rig" as these aren't just simply "power amps"???
For the amp name: SmokinG 88 because then your name SG stands out (pretty obvious yeah?)
-
This thing pulls B+ down in a big way....unloaded I'm around 460VDC(ish)
This is what I figured and why the earlier suggestions of getting that B+ up the higher 400s.
What did you end up doing about the driving tube situation?
I think you should name the thread "Stereo SE KT88 amps for live rig" as these aren't just simply "power amps"???
For the amp name: SmokinG 88 because then your name SG stands out (pretty obvious yeah?)
Oh yes Sir...I was listening about the B+ conundrum....had to see/hear it for myself and once I did I knew you were right.
I was thinking more about limiting output power with B+ and didn't realize the effect on headroom until I saw it on the scope.
Very glad everyone is here and hung in there with me....well, almost everyone.
I told you he was gonna start....I still swear he's like Beetlejuice, where if he comes up 3 times in a thread you can be sure he's gonna show up spouting off about something. It doesn't even have to be his name....just strat, KT88, tele, major, Ritchie, Blackmore, DP, the color purple,,,anything deep....etc., etc., etc., etc.,
At one point he pm'd me and said some crap like "THE GODS OF BLACKMORE HELLFIRE WILL RAIN DOWN UPON THEE"
What does that even mean?
I like the name suggestion.
The SG88...has a nice ring to it
Driving tube(s) is as it was in the schematic, single AU7 into parallel AU7 into KT...nothin fancy
-
SG I'm reminded of a long ago discussion regarding Plate Resistance rather than Tube Gain as being a prominent factor for consideration of design and how your adjectives are seemingly spot on to this. In using the au7s not just in a single stage or two but in all of the preamp stages - you are substantially increasing the bandwidth of the entire amp and remember, the greater the BW, the more “sparkle” and “chime” we’re likely to perceive.
-
mojo758. drops right in stout chassis. B+ should be about 440V
doug gets them for 112 bux.
make that 88 sweat. squeeeze it!
--pete
-
Why is rp (ohms) listed twice? And why the rp and rp'?
-
Why is rp (ohms) listed twice? And why the rp and rp'?
One is it's listed "static" value and one is the actual "dynamic" value in operation. When you see the apostrophe you would say "prime" as in "rp prime"?
-
... your adjectives are seemingly spot on to this. In using the au7s not just in a single stage or two but in all of the preamp
Ah-Ha!....I knew there had to be a reason for this awfully large head.
I think the AU7 gets a bad rap....in the guitar amp world.
I recently started with a 5F6-A 'ish design and sat with the guy for 15 different tweaking sessions and wound up with 1- parallel AY7, 2- AU7 gain stages and an AU7 FX loop in the preamp....got lots of drive without a lot of clipping
The guy is thrilled and thinks there's magic dust in there....in reality it's just the effect of cascaded 'low gain' stages.
So that carried over to this design and I wouldn't do anything differently....the Triaxis into this amp is literally the best amp tone I have had at my bench since I started. Especially the pushed clean sound which retains note separation and clarity, but feels rubbery and spanky.
The distortion is just how Dr. Destructo described it and offers up an edge I've never heard before...had to drive the grid to get there, but man am I happy I did.
-
Thanks Jojo. :icon_biggrin:
-
mojo758. drops right in stout chassis. B+ should be about 440V
doug gets them for 112 bux.
make that 88 sweat. squeeeze it!
--pete
there must be a name for the illness we suffer from
One thing I didn't address which will make an easy addition if deemed valuable:
Would you guys put a B+ fuse on the OT like I had on the breadboard, and what approx. value? (I used an 1/8 amp SB)
DL said OT is rated @ 120mA
Does placement matter? between B+ rail and OT or between plate and OT?
?
-
use a 250mA fuse replace with 500mA if it pops.
--pete
-
there must be a name for the illness we suffer from
there is no cure. we can only treat the symptoms with doses of inductors.
--pete
-
there must be a name for the illness we suffer from
there is no cure. we can only treat the symptoms with doses of inductors.
--pete
Oh I thought we could transform ourselves into some output that was better?
~Phil
-
After extensive play testing I have determined that I was wrong about a few things...
-I thought it was gonna be perfectly mated up with a Greenback G12M-25...nope, can't handle it
--Plugged it into my Eminence EM-12 and it took over...much wider response, and no speaker mud at all
-I thought I could handle 2 of the same amp for a stereo pair, but I'm gonna still need more clean headroom, for clean tones and effects.
--I'll make the next one push-pull, and I'm thinkin' 6L6 so hopefully when I blend them together they will fill each other out. (?)
I'll get it laid out on the other board and see what happens.....Board Wars...it's the only way.
there must be a name for the illness we suffer from
there is no cure. we can only treat the symptoms with doses of inductors.
--pete
...or bridge rectifiers (seeing how I now have a large stock of those )
And so we go on......................
-
the AU7 gets a bad rap
+1
my next - current build is a 2 tube AU pre, thanks to PRR for helping dink out the kinks, driving a PSE 6V6
there is no cure
:nice1:
-
After extensive play testing I have determined that I was wrong about a few things...
-I thought it was gonna be perfectly mated up with a Greenback G12M-25...nope, can't handle it
--Plugged it into my Eminence EM-12 and it took over...much wider response, and no speaker mud at all
-I thought I could handle 2 of the same amp for a stereo pair, but I'm gonna still need more clean headroom, for clean tones and effects.
--I'll make the next one push-pull, and I'm thinkin' 6L6 so hopefully when I blend them together they will fill each other out. (?)
I'll get it laid out on the other board and see what happens.....Board Wars...it's the only way.
there must be a name for the illness we suffer from
there is no cure. we can only treat the symptoms with doses of inductors.
--pete
...or bridge rectifiers (seeing how I now have a large stock of those )
And so we go on......................
i know nothing of what you speak. :angel
--pete
-
Pete, how many of those things do you have? :l2:
-
Pete, how many of those things do you have? :l2:
i had 2k. it's a smaller pile now... :icon_biggrin:
--pete
-
How did you come to have so many?
-
-I thought I could handle 2 of the same amp for a stereo pair, but I'm gonna still need more clean headroom, for clean tones and effects.
The reason I suggested KT-88's (on page 1) is that I thought they were the best SE approach to sufficient clean headroom. Which raises the musical question: where is the dirt in the power amp coming from -- the small bottles, the big bottles or both? If it's the small bottles, you might get more clean headroom from a higher mu tube, despite your affection for the 12au7.
Also, if you add a second identical amp & speaker, you will get a 6dB boost, which may be good enough: 3dB for double amp power + 3dB for double the speaker cone area.
You can measure this stuff. To judge this you need an SPL meter. These can be downloaded for free on your smartphone, but these programs don't work well below 100Hz. Or, for about $35 Radio Shack SPL meters are good enough & are used by pro's and can measure down to 50Hz. So play a guitar passage (above 100 Hz for a smartphone SPL). Note the SPL level. Record your passage; play it back through the power amp or your hi-fi. Turn up the vol of the playback until it matches the SPL of the original passage. Then turn it up more until the SPL meter reads 6dB more. Now you will hear the SPL level of 2 identical amp-speakers, before building anything.
-
How did you come to have so many?
m.c. howard surplus store. closed sometime around 2008. richard and i bought 4 packs of 500 for a $20 bill.
--pete
-
-I thought I could handle 2 of the same amp for a stereo pair, but I'm gonna still need more clean headroom, for clean tones and effects.
The reason I suggested KT-88's (on page 1) is that I thought they were the best SE approach to sufficient clean headroom. Which raises the musical question: where is the dirt in the power amp coming from -- the small bottles, the big bottles or both? If it's the small bottles, you might get more clean headroom from a higher mu tube, despite your affection for the 12au7.
Also, if you add a second identical amp & speaker, you will get a 6dB boost, which may be good enough: 3dB for double amp power + 3dB for double the speaker cone area.
Some of my thought comes from the idea that I won't need this much KT character and drive X 2
I got this amp to a point where I love it and the drive is incredible and I now I cant turn around,,,so that's enough of that for the DRY side.
The character of the KT88 is there and it stings like a bee.
So now I'm thinking I want the other side to be a cleaner reproduction (or my vision of "more headroom") so that the cleans don't drive so hard and there will be enough "headroom" to reproduce the effects well....this side should float like a butterfly.
And I'm thinking of a p-p setup for that so it will be a lot like running 2 completely different amps (through different speakers) at the same time where they fill each other out. I just don't think it would be the best idea to duplicate the 88 amp and wind up with too much of this good thing.
As far as the 12AU7s go....it's time for me to learn something because I thought I was using this tube to provide the biggest swing without clipping.
The KT88 output appears to square before the input signal does AFAICT,,,but that character is worth keeping, and it cleans up just enough as I turn the volume down on the geetar so that it is useable (and desireable).
Going forward I will need to figure out how to drive the p-p side cleaner, so if a higher mu tube will do it 'better', I'm all ears.
It is counter-intuitive to my thoughts about 'gain' to use a higher mu tube for 'less gain'(?)
One last thing, while I'm typing...
Even though I like the EM-12 speaker better than the Greenback, it just opened my eyes to the possibility of the speaker's effect.
I'm not sold on the EM-12 as THE speaker for the KT88 (dry) side, but at least now I won't just settle for the Greenback because I thought it was the 'right' choice.
I will probably wind up using the EM-12 as more of a full-range speaker for the p-p (wet) side, and keep experimenting with different single 12"s until I find one that matches the character of the 88 output. The Greenback sounded congested. The speaker in the pic below is the G12H-30 70th anniv. and it has way too much 'sizzle' to pair well with the 88.
I'm gonna look at some frequency curve charts and see if something stands out that will counteract the extended response of the EM-12
Here's the other cab I'm building for the 88 to push...it will be fully open back, and angled up like this to act as a monitor.
-
Sounds like a good way to go.
Meanwhile, I've searched the web for a useful image of a 12au7 loadline, w/o success. I think that a typical 12au7 loadline runs pretty close to the X-axis; closer than typical for a 12ax7. The result is that the 12au7 has less voltage swing, before the bottom of the curve cuts-off, or the top saturates. That's OK because the 12au7 has little mu anyway. You can get more clean voltage swing from a 12ax7. If the output voltage is too high for the next stage, it can be cut back with a voltage divider.
OTOH, sometimes people think of headroom in terms of how far they can rotate the vol knob before overdrive kicks in: more rotation = more headroom. Of course, with a lower mu tube, the vol knob can be further turned up and maybe never overdrive: "infinite headroom" :icon_biggrin: . But the overall vol of the amp may be lower.
-
It is counter-intuitive to my thoughts about 'gain' to use a higher mu tube for 'less gain'(?)
From what I understand, the tube can get a lot louder (due to higher u) without distorting, therefore has more headroom. you can turn it up to 70% of its capacity and it is at 70 u and still clean, whereas for lesser amplification of say a 12AU7, it causes the breakup at its '70%' point which is like u of maybe 25 or something (I think its about 30 on that one?).
I could be completely out in the dark, considering how new I am to this though :P (I'm an older nerd though so I read like a madman, and have less practical experience. So the concepts are sinking in faster than the actual use type stuff).
As far as a load line, you're right, I did one based on the design of my recent Vox AC100 with the preamp input 12AU7, and it was really low down on the curves, unlike the 12AX7 with identical 100k Anode and 1.5k Cathode resistors. It was odd to me to see, but it makes sense now that I think about it. I'll have to get that image I created and post it here to show it compared to load lines we've probably all seen for the 12AX7. (its at home and I'm at work)
~Phil
-
Meanwhile, I've searched the web for a useful image of a 12au7 loadline, w/o success. I think that a typical 12au7 loadline runs pretty close to the X-axis; closer than typical for a 12ax7. The result is that the 12au7 has less voltage swing, before the bottom of the curve cuts-off, or the top saturates. That's OK because the 12au7 has little mu anyway. You can get more clean voltage swing from a 12ax7. If the output voltage is too high for the next stage, it can be cut back with a voltage divider.
This is a great time to make sure I am getting this right....
I choose the AU7 at these operating conditions because I wanted low gain that could handle a big swing cleanly.
Looking at these load lines, I would think that the AU7 does a much better job of not clipping than an AX7 that is biased relatively similar.
(I use PRR's rule of thumb equation that I took as meaning---center bias can be approximated this way:
relation of plate resistor value to cathode resistor value should be approx. rk x mu = ra )
So I have the AU7 @ 47K ra with 2.2K rk
...and the AX7 @ 100K ra with 1K rk
If I'm seeing this wrong I would love to get it right.
-
(I'm an older nerd though so I read like a madman, and have less practical experience. So the concepts are sinking in faster than the actual use type stuff).
p-sneaks, and anyone else who may be lurking and learning....
I found this video to be helpful in seeing this concept.
jj, and others will straighten me out and we all can learn something here.
https://vimeo.com/33244955 (https://vimeo.com/33244955)
-
I will check the video, I thought that the load line should include the cathode, so you should do 49.2k not 47,k on that 12au7? no?
I have been doing a lot of reading, bought the valve wizards preamp design book and am almost done, the first chapter covers a lot of this, but again, it is all book learning so I could be way off. He mentions going too low down on the scale becomes difficult because it causes more current to flow, and more current clipping.
I also think maybe I'm confusing headroom and volume. The lower the slope is, as above, the higher the current, the lower distortion, and the higher the voltage swing. This means more headroom. This doesn't specifically mean more volume. I.e. you get a cleaner tone right up until the tube hits maximum output. The volume is what I meant 'goes up and stays clean' with a higher u tube. i.e. if they were both biased with identical headroom, the 12AX7 would be louder and still clean because it has more magnification no? On the other hand, if you were to bias a 12AU7 so that it has a low slope and high headroom, and then a 12AX7 with more chance of OD and the slope is up higher (negative slope for both of course) the more crunch you get at output from the 12AX7 at higher input, but you also get more overall volume due to the tube having higher u. In theory, if balanced right, the 12AX7 could have more volume at lower input, without distortion, than a more headroom biased 12AU7 just due to its u factor.
I was calling it headroom and meant volume. I hope that clarifies it?
If someone can help me understand what I'm missing please do :)
I'm guessing one of the PRR/Sluckey/Willabe guru gents is going to show where my thinking is wrong :D
Edit: worded it as 'I'm confusing' not 'we're' because it may more be me than anything lol
~Phil
-
The question on including the cathode resistor in the line, comes from this image example from his book.
I.e. you do the load line without it initially in trying to get a general idea, but once you add the chosen cathode resistor in, you use it for both the load line and the bias line.
See attached image.
~Phil
-
If someone can help me understand what I'm missing please do :)
I'm guessing one of the PRR/Sluckey/Willabe guru gents is going to show where my thinking is wrong :D
You can always start a fresh thread with those questions/comments and some of the guys will be happy to teach you.
This stuff can get hidden and overlooked in these marathon threads and I imagine some guys give up on these threads once we start drifting off topic.
-
Oh no worries, I was just trying to talk about what you were about the reason that you were told a 12AX7 would give you more... I'm just enjoying this thread a ton overall seeing the cool stuff you do to create circuits from scratch etc. I'm still so far away from that it's not funny :P
If what I'm saying is right, and helps, I'll be stoked because it means I'm starting to make positive progress lol. If I'm not, I won't be shocked.
~Phil
-
p-sneaks, and anyone else who may be lurking and learning....
This stuff can get hidden and overlooked in these marathon threads and I imagine some guys give up on these threads once we start drifting off topic.
:sleepy2: :hello: :l2:
-
Oh no worries, I was just trying to talk about what you were about the reason that you were told a 12AX7 would give you more... I'm just enjoying this thread a ton overall seeing the cool stuff you do to create circuits from scratch etc. I'm still so far away from that it's not funny :P
If what I'm saying is right, and helps, I'll be stoked because it means I'm starting to make positive progress lol. If I'm not, I won't be shocked.
and I hope you know I meant no disrespect...
If you wind up watching that video, make sure you make it through to about 3:30 (and on)...that was an eye opener for me as far as how to interpret what you see on the load line and how it applies to application of that info.
The addition of the cathode resistor on the load line would have a miniscule effect on the outcome, but your point IS good :thumbsup:
:sleepy2: :hello: :l2:
So back to the idea of headroom...
It has different meanings to different people and can appear subjective in that way because it can apply to distortion vs. clean potential. I should have said "more clean headroom all the way through the power amp", so a clean input signal will result in a clean output signal.
I would like more clean headroom but not more volume...which is tricky, but in this case maybe easy. Just make an amp that is capable of being louder than what I will use and then just keep the input volume to a point where it not creating any OD. I imagine that this wet amp will not have to be turned up as loud as the 88.
With the next amp I hope to accomplish a cleaner signal path all the way through the output tubes, which means I won't want to drive the grids as hard as I did the 88 (where I believe the majority of the overdrive is coming from)
So maybe fixed bias 6L6s and less signal gain overall....and maybe just a single AU7 driver stage into a AU7 phase inverter (?)
I guess that's what I'll try 1st...my instincts seem to be ok so far
I hope someone goes back 6-7 posts and catches my question (without a question mark) so I can be sure I'm not misinformed...pleas correct or confirm me so I can jump over that mental hurdle.
-
The shortened version: to bias a valve with respect to the load line involves several pages of explanation. To bias a valve towards Vg=0 is to bias towards grid current limiting (saturation) and when this is exceeded you are clipping the input grid signal even though the output appears that the negative half of the wave sign is flattened and appears clipped.
To bias to the lower right end of the scale - depending on which set of curves you're looking at -4 to -8 and more is at some point to where current is to have cut-off and the whole B+ of the valve is dropped across it. In this condition it really is the output signal that is forced to clip, and not the input signal.
If the bias pointis chosen near the right-hand end of the load line, cut-off clipping will occur on the positive side of the output signal. If the bias point were chosen to be roughly in the middle of the grid
curves we could produce a signal that is clipped roughly equally on both sides, though it would take a larger input signal to do it. This is known as centre biasing and it offers the maximum threshold of clipping, or to give it its informal term highest headroom.
At the same time, we would be able to feed the grid with the largest possible signal before clipping, or in other words, the input sensitivity of the stage is at its lowest (input sensitivity is simply the input voltage required to drive the stage to the point of first clipping). Biasing at any other point on the load line will reduce the maximum size of input signal before clipping is reached, reducing headroom and making the stage more sensitive.
-
Looking at the loadline plots in SG's Reply #193. Assume a Les Paul sends 1/2V of signal (500mV) into an amp's input stage. That's a 1/4V swing to either side of the bias point.
* For the 12ax7: Looks to me that a 1/4V swing to either side of the bias point, causes plate voltage to swing 25V (= 190V - 165V)
* For the 12au7: the same input voltage causes plate voltage to swing only 10V (= 155V - 145V).
Clearly the 12ax7 can output a clean signal wave of larger amplitude (headroom).
-
Looking at the loadline plots in SG's Reply #193. Assume a Les Paul sends 1/2V of signal (500mV) into an amp's input stage. That's a 1/4V swing to either side of the bias point.
* For the 12ax7: Looks to me that a 1/4V swing to either side of the bias point, causes plate voltage to swing 25V (= 190V - 165V)
* For the 12au7: the same input voltage causes plate voltage to swing only 10V (= 155V - 145V).
Clearly the 12ax7 can output a clean signal wave of larger amplitude (headroom).
There's the math that I think was exactly what I was trying to explain too. Sorry I didn't explain it very well. Or at least it seems to me that is precisely what I understood and was trying to explain :)
~Phil
-
So back to the idea of headroom...
I would like more clean headroom but not more volume...which is tricky, but in this case maybe easy. Just make an amp that is capable of being louder than what I will use and then just keep the input volume to a point where it not creating any OD. I imagine that this wet amp will not have to be turned up as loud as the 88.
So maybe fixed bias 6L6s and less signal gain overall....and maybe just a single AU7 driver stage into a AU7 phase inverter (?)
I guess that's what I'll try 1st...my instincts seem to be ok so far
6L6?!?!?! Have I taught you nothing.... :dontknow: Ok, you have come this far, Grasshopper.... It's time to burn the KT88 brand onto your forearms and complete your training. :happy2:
It just so happens there is a perfect amplifier that utilizes KT88's in an UL configuration with a AU7 driver/inverter. Our partner in crime, Tubenit has posted a full blown schematic. All you need to do is cut the end off. Loads of clean headroom. Loads of glorious KT88 tone. "Major Guns" (TM)
Finish this, my son, and seared into your flesh are the signs that will inevitably identify you before the world; on your left forearm, the sign of Deep Purple; on your right, the sign of a Strat. The Marks of Ritchie.
Amituofo....
Jim
-
Finish this, my son, and seared into your flesh are the signs that will inevitably identify you before the world; on your left forearm, the sign of Deep Purple; on your right, the sign of a Strat. The Marks of Ritchie.
Put the bong away man...
NOBODY needs that much VOLUME
NO more 88's, no UL, no Strat,,,get over it.
It's 2016 and no one likes loud guitar anymore.
You sound like a raving lunatic.
By 2025 the only things KT88s will be used for is heating up food and tanning, so I imagine supply will dwindle and become even MORE expensive, but you don't care 'cause you'll be 80 and sitting on a stack of Gold Lions....can you at least pencil me a few in your will?
Oh, and The Major is basically an ugly, inefficient space heater....put it in The Smithsonian where it belongs, and pick up a Justin Bieber album while you're out.
-
Looking at the loadline plots in SG's Reply #193. Assume a Les Paul sends 1/2V of signal (500mV) into an amp's input stage. That's a 1/4V swing to either side of the bias point.
* For the 12ax7: Looks to me that a 1/4V swing to either side of the bias point, causes plate voltage to swing 25V (= 190V - 165V)
* For the 12au7: the same input voltage causes plate voltage to swing only 10V (= 155V - 145V).
Clearly the 12ax7 can output a clean signal wave of larger amplitude (headroom).
Thanks JJ...I get it
I was focused more on the input signal, and which tube would do a better job of handling the bigger signal that would inevitably be coming from the preamp.
-
....This is known as centre biasing and it offers the maximum threshold of clipping, or to give it its informal term highest headroom.
At the same time, we would be able to feed the grid with the largest possible signal before clipping, or in other words, the input sensitivity of the stage is at its lowest (input sensitivity is simply the input voltage required to drive the stage to the point of first clipping). Biasing at any other point on the load line will reduce the maximum size of input signal before clipping is reached, reducing headroom and making the stage more sensitive.
That's what I was thinking jojo and you confirmed my thoughts about using the AU7 for it's ability to take in a large signal.
I have to be careful with the term headroom because it does take on different meanings in different context. (in my mind at least)
So I set the first stage at about -6V and then the following parallel stage at about -10V, in hopes that that second stage could stay clean'ish
then...
Tonight I set up the p-p 6L6 board and had a AU7 input driver feeding an AU7 PI ,,,and I left the 1st stage cathode un-bypassed (to lower input sensitivity) and that seemed to help...
Didn't have a lot of time to play, but I was able to hear a cleaner signal, and with the addition of NFB I was able to get it much cleaner and closer to right.
I'll get back to it soon and I think I'm on the right track with the 6L6s....regardless of the peanut gallery.
-
I was able to hear a cleaner signal
fwiw, I've scoped each stage, using 4 different frequencies (100hz, 800hz, 1.5K-ish, and 4k). If it's clean for all 4, move to the next stage. It's a pain in the *^&*, but it *shows* you where the signal gets *bent*
then you can listen and say, ya, that's a good bent. Anyway, it's "one more tool" I use to try n keep everything clean, but, well it's bong time :icon_biggrin:
-
SG - you need to put a load line on Jimbo's input sensitivity (aka headroom) to provide the proper bias to the old guy's plate resistance knowing his gain factor is augmented at the mere mention of the renaissance period of DP & Blackmore ... :l2:
(lucky dog having that breadboard paying off once again)
Earlier I forgot you had your triaxis preamp feeding into this power amp design, my bad. :dontknow:
Shooter - good "stash" of info there :wink:
-
:sad2:
Jim
-
BTW, how loud do you think two 6L6's are going to be? :dontknow: Why not use a tube that at least sounds good!
Jim
-
You sound like a raving lunatic.
By 2025 the only things KT88s will be used for is heating up food and tanning, so I imagine supply will dwindle and become even MORE expensive, but you don't care 'cause you'll be 80 and sitting on a stack of Gold Lions....can you at least pencil me a few in your will?
Oh, and The Major is basically an ugly, inefficient space heater....put it in The Smithsonian where it belongs, and pick up a Justin Bieber album while you're out.
All right, I'm throwing several flags on this play, definite unnecessary roughness, taunting the other team, ........
:angry:
-
> I thought that the load line should include the cathode
It depends.
But for any Mu which is "interesting" (say, 20 or more), the difference is insignificant.
49.2K or 47K.... well, that's just resistor-slop, right? Even a bridge designer can't work to 5% accuracy.
> maybe I'm confusing headroom and volume
That happens a lot.
-
It's good to get another CIVILIZED response backing up my attempt at edjumacating the uninformed and weak minded. The upper crust like us must stick together. :occasion14:
Raving lunatic.....HA!
Jim
-
:rolleyes: Not helping Jimbob. :lipsrsealed:
-
:sad2:
Jim
:rolleyes: Not helping Jimbob. :lipsrsealed:
Yes,,, now hush up and let the adults finish talking.
Whats next....he'll want me to wear a wig and dress like a pirate?
-
I was able to hear a cleaner signal
fwiw, I've scoped each stage, using 4 different frequencies (100hz, 800hz, 1.5K-ish, and 4k). If it's clean for all 4, move to the next stage. It's a pain in the *^&*, but it *shows* you where the signal gets *bent*
then you can listen and say, ya, that's a good bent. Anyway, it's "one more tool" I use to try n keep everything clean, but, well it's bong time :icon_biggrin:
I've been using an abbreviated version of that technique and never thought to change frequencies during the tests...thanks for mentioning
-
Yes,,, now hush up and let the adults finish talking.
Come on, really? :BangHead: :offtopic1:
-
I had some luck with NFB last night but didn't go very far with it.
Anyone want to talk about what is happening as a result of this NFB configuration?...or what design objective there is?
-
I was focused more on the input signal, and which tube would do a better job of handling the bigger signal that would inevitably be coming from the preamp.
But a big signal from the Triaxis is not inevitable; instead it's fully adjustable. The Triaxis has numerous (maybe mind-boggling at first) controls which affect the voltage level of its output signal, with a final output master control. Whatever hi gain, etc., taking place within the Triaxis, gets tamed on the way out for input into the next device, like your power amp. So there's no limit to input tube choices for the power amp.
Any tube at your power amp's input stage will likely have enough mu to swamp the input of the next small bottle tube. So a voltage divider may in order. But it's not clear that a second small bottle gain stage is needed. The only requirement is to drive, and overdrive, the KT-88.
Looks like the KT-88 can take almost 30VAC of signal and stay clean (given SE bias of around -14V). Clean signal voltage can be up to 2X bias voltage. Assuming you can output 1VAC signal form the Triaxis, one 12ax7 in the power amp might accomplish the purpose of driving and over-driving the KT-88. Note that you don't need the small small bottle tube(s) to distort in the power amp, because all that tone shaping already happened in the Triaxis.
Maybe a lower mu driver tube can take a certain input voltage and convert it to more than 30 signal volts to overdrive the KT-88. It's a matter of plotting it out for tube types that you like.
-
> I thought that the load line should include the cathode
It depends.
But for any Mu which is "interesting" (say, 20 or more), the difference is insignificant.
49.2K or 47K.... well, that's just resistor-slop, right? Even a bridge designer can't work to 5% accuracy.
> maybe I'm confusing headroom and volume
That happens a lot.
PRR, great information, thanks!
Now back to the jamming that was going on in this thread :D
:m8
~Phil
-
SG, I have been running 2 amps, wet and dry for almost as long as I have been playing. If you main Dry is going to be the KT88 SE amp and it has a controllable volume for a small venue you are more than half way there. I will question to use of 6L6 on Push Pull. I just do not think running a push pull amp clean against a hard driven SE amp will benefit much. The reason is all tube amps sound very similar at low volumes.
My point is a clean amp in a band situation, even if it has a little verb or delay, will cut through and seem much louder than a distorted amp. I am intentionally not going to mention "headroom" since if I understand you are wanting to have a 2, 12 inch speakers. One running dry and overdriven which makes this one not cut through as easily. The idea of filling in with the PP 6L6 I am not sure you will be able to get enough volume to hear the 6l6 character. If you do it will swamp the KT88 amp, even if you shoot for class A at about 25 watts like the Carr Rambler.
I could be way off base here, but in my experience I have had better results with the wet amp having lower volume and I really do not like the sound of a tube amp with the volume low. Of course you do not want to overdrive modulation effects, but any processor I have ever used sounds great if the tubes in the power amp are working hard. If they are not the tone sounds sterile and I have been in this situation. In this case sending the wet to a Peavey Bandit Solid State amp is what I used to do. I know it is blasphemy to say, but to me a solid state amp with a great speaker sounds better at lower volumes than choking down a tube amp does.
I am not trying to tell you what to do, just share what I have found. When we dream of the perfect rig one variable we do not know is how is it going to sound in a live situation with a Bass, Drums and what else you may be playing with.
-
Ed, I ALWAYS appreciate ALL of your input because it is based in real world experience with a rig similar to what I'm trying to put together here, besides the fact that I know you have a great ear and good taste.. I am questioning all of these issues but trying to make decisions and move forward based on what I know. (even considering a Blue for the dry 1x12")
I'm glad that you're speaking up before I wind up settling for something and never realizing the rigs full potential.
The main reason I went this route is because of my previous experience of using the Simul 395 power amp (4-6L6 per side @ 95W per side). I had to throttle it back so far that it never sounded great to me until I got to an outdoor show and was able to open her up....those days are gone.
The SG88 is done and I'm happy with the amount of control between driving stages...it never really cleans up all the way, but I like the character of driving the 88, and the max volume is perfect for a baseline to build the wet rig onto.
So yes, I need to know what that volume relationship is in the real world.
50/50, 40/60....whatever it is, your input gets me closer to that understanding.
If the wet rig will be less that 30-40% of the overall output, than maybe we talk about an SE 6L6 with fixed bias?...with a single AU7 driver?
Is there enough headroom there for the FX?.....or are you thinking 2-6V6?
Some of the reason I was leaning towards p-p was the "idea" that it would create a more complex monster by combing the 2 output types.(not to mention the different tube types)
I think 2 SE amps running together will be plenty loud for the application.
-
I was focused more on the input signal, and which tube would do a better job of handling the bigger signal that would inevitably be coming from the preamp.
But a big signal from the Triaxis is not inevitable; instead it's fully adjustable. The Triaxis has numerous (maybe mind-boggling at first) controls which affect the voltage level of its output signal, with a final output master control. Whatever hi gain, etc., taking place within the Triaxis, gets tamed on the way out for input into the next device, like your power amp. So there's no limit to input tube choices for the power amp.
There's definitely a 'sweet spot' in the Triaxis, and although it would appear to be infinitely adjustable it actually winds up sounding thin/anemic at lower settings and squeals like a pig at higher settings.
So I still like the AU7 for the input driver...and maybe even unbypassed for less sensitivity...and then a next stage to drive the output tubes at least enough to get some character out of them. I might have made a mistake by paralleling the AU7 second stage in the SG88, but once I got that much drive going it just came to life and the heavens opened up and I heard angels singing.
I haven't thought to measure the output signal V of the Triaxis (in it's sweetspot), but I can do that tonight to get us a ballpark.
-
SG, I was just re-watching a Tim Pierce & Pete Thorn vid w/ Josh Smith (all unbelievably talented). At the 17:30 point or just after they discuss their wet/dry rig set-ups. I was thinking mainly of Ed's comments regarding using his AC15/Princeton combo (2 x 6V6) and this seems to be what many are doing these days (using two amps). But the entire video - albeit long, is worth watching at least once. Ed - you too. I loved how they describe the Princeton as being "the pillow". I would think this type of amp with 6V6's should be plenty of volume and headroom for the gigs you want to play? There's something in this for most everyone to take away with them regarding Strats, Tele's, & Gibsons, string gauges, effects, carbon batteries, a good Dumble story, recording info, etc.
Also, I agree on overall volume/power. In my gigs we're always being careful of overpowering the audience, especially if you lay back the speaker cabs pointing upwardly at you.
https://youtu.be/v7XoL4USZpY (https://youtu.be/v7XoL4USZpY)
! No longer available (http://www.youtube.com/watch?v=v7XoL4USZpY&feature=youtu.be&inf_contact_key=741b34dd8e8679228ac4392cce5dff88a553cfc6c431927c587292e1635dfe92#)
-
I have already seen the video. Good info.
SG, The overall tone is subjective and certainly your preference and I have no doubt you can tweak it to sound like you like. I am not going to suggest any particular topology, I just think you may want to test your reasoning.
For instance, a Triaxis fed to front of house sounds fine to the audience. I have a friend who does just that and I have played his rig. Feels very sterile and his band sounds like listening to the radio with everything compressed coming out of the house system. They are a very popular band and work a lot so they are well liked. They play 70's POP and their shows are fun. His rig is not very inspiring, but it performs the job well.
I wrote this to say his rig feels like mine when I am using a processor playing through low volume amp. The 2 magic components are missing. Tube tone and air movement from speakers. One you can get back since you are planning to use 12's for speakers and that is the tube tone.
Anything you build push pull has the potential of overpowering the SE amp. 10 Watts clean added to what you already have is quite a bit and your effects like chorus and your dealy will take on a more analogue sound if you can get the tubes working enough to color the sound.
-
Anything you build push pull has the potential of overpowering the SE amp. 10 Watts clean added to what you already have is quite a bit and your effects like chorus and your dealy will take on a more analogue sound if you can get the tubes working enough to color the sound.
10/4
I'll give the SE board another shot before I start soldering.
I've never seen a design with NFB on SE, so maybe that's something to consider...(?)
I DO NOT want that other guy's sound and it would undermine my entire goal.
If my tone doesn't inspire me I will not want to be out there, that's why I built the one cab to point at my head.
The idea of going back to a processor and preamp makes me sad enough...it's gonna have to sound good.
Thanks for the video jojo,
Big talent and cool tones there...
If I ever start talking about the effect of different batteries in my pedals I would hope someone would point me to a good therapist.
Ok, yes there is a difference in battery sag, but if I'm splitting those hairs it would make me nuts.
Also, that pedalboard gives me a headache just looking at it, and would be a sure stage obstacle in the little corners we have to squeeze into these days. I think Pete Thorn does some great demos, and his G system video helped me get hooked, although I won't be utilizing the insert loops because I have no pedals that I am attached to.
https://www.youtube.com/watch?v=5uz9WiPKXA4 (https://www.youtube.com/watch?v=5uz9WiPKXA4)
-
...although I won't be utilizing the insert loops because I have no pedals that I am attached to.
:w2: But you haven't tried one of mine? :rolleyes: (sorry for the shameless plug :dontknow: )
-
:w2: But you haven't tried one of mine? :rolleyes: (sorry for the shameless plug :dontknow: )
No problem jojo, this thread is already a roller coaster
If I cant get THIS rig sounding good I will be taking up a new sport.
So, sadly,, I may never own one of those beauties.
I'm going Triaxis, G system, power amps, speakers, done.....noooo more variables :BangHead:
-
SG "Justin Beiber" aaackk! LOL
-
SG: Seems like the term "headroom" is a bit elastic. Here's a 12au7 thread where it's used in the sense you were using it, re the ability of the 12au7 to handle bigger swings in input voltage: http://archive.ampage.org/threads/1/open/016845/12AU7-1.html (http://archive.ampage.org/threads/1/open/016845/12AU7-1.html)
It would be interesting to know the voltage output of the Triaxis' sweet-spot.
-
It would be interesting to know the voltage output of the Triaxis' sweet-spot.
Here's some quick results...based on presets that I would be likely to use.
And yes, the available range of adjustability IS ridiculous, so these are just some ballpark readings so you know where we are.
Feeding in 400hz @ 500mA
Clean tone: (programmable master out on 3.5 for min, and 6.0 for max)
min 8vac p-p
max 14v p-p ...starts going square and I don't think I've ever had that programmable master control that high on a clean preset
High Gain:(same master settings min/max)
min 2.4vac p-p
max 8.4v p-p
Main output pot at 50% (that's the 25K pot we saw earlier in the thread)
I think my results can be more accurate once I get some presets programmed in where the audible levels stay the same when I switch from clean to dirt
-
Ed, does that Princeton give you enough volume? I've got a 2x6V6 amp and it gets into the power tubes pretty quick when you turn up the wick. I don't think I could have ever played out with it, even if it was miced. Just not enough volume. Headroom is not what I think of with 6v6's either. I remember my old Bandmaster would completely bury it running wide open with relative ease.
I don't know SG, I still think a couple of KT88's loping along would give you plenty of - lets just say room!
And yes, a wig and hat would look good on you. Anything to cover that Flock of Seaguls hairstyle you have.
Jim :icon_biggrin:
-
FWIW it seems the Triaxis is supposed to feed the Mesa Boogie 2-90. Schematic here: http://schematicheaven.net/mesaboogie.html (http://schematicheaven.net/mesaboogie.html)
Anyway that's how Mesa Boogie handled the input stage fed by the Triaxis.
-
I've never seen a design with NFB on SE
I played around with it on a couple *audio* builds, didn't really do much at lower volumes and dimed it seemed to make the *mean* meaner, in a bad way.
I got lost, is your PP 6L6 fixed or self biased?
-
I've never seen a design with NFB on SE
I played around with it on a couple *audio* builds, didn't really do much at lower volumes and dimed it seemed to make the *mean* meaner, in a bad way.
I got lost, is your PP 6L6 fixed or self biased?
Fender Champ...
-
FWIW it seems the Triaxis is supposed to feed the Mesa Boogie 2-90. Schematic here: http://schematicheaven.net/mesaboogie.html (http://schematicheaven.net/mesaboogie.html)
Anyway that's how Mesa Boogie handled the input stage fed by the Triaxis.
Looks a little squirrel'y to me...The 2:90 manual states that the common setup is to use the 'line' in, which looks to me like that creates a 1.5K input impedance
Why would you want to knock down the incoming signal that much?...and doesn't that create an input condition that is opposite of what you would want for proper impedance matching?
-
Ed, does that Princeton give you enough volume? I've got a 2x6V6 amp and it gets into the power tubes pretty quick when you turn up the wick. I don't think I could have ever played out with it, even if it was miced. Just not enough volume. Headroom is not what I think of with 6v6's either. I remember my old Bandmaster would completely bury it running wide open with relative ease.
I don't know SG, I still think a couple of KT88's loping along would give you plenty of - lets just say room!
And yes, a wig and hat would look good on you. Anything to cover that Flock of Seaguls hairstyle you have.
Jim :icon_biggrin:
Ed is 100% right in his above post about overpowering the SG88 with any PP amp and I'll tell you why...
I went out last night and tried to run 2-6L6s in PP (fixed bias, shooter) at a lower volume, and it just sounded very sterile. By the time I got it loud enough that I was spanking those 6L6s, and the magic was happening, it would have wound up being twice as loud as the SE 88 and way too loud for any room I'm gonna be allowed in.
That's why 2- KT88s aint gonna happen,,,because loping around isn't the same as force feeding electrons through an OT, and if the 6L6s are too much than a 1/2 Major is waaaay too much.
So I put the PP board away and went back to the SE board where I will now try to beat a 6L6 into cooperating.
If you're lucky I might just wind up going back to another SE KT88 like DL suggested multiple pages ago.
Sometimes, in life, we must walk over mountains to realize that what we were looking for was where we started. (write that down)
-
Why not try two 6V6s and if that's still too loud try two 6AQ5s or 6BM8s? Just because 6L6s are too loud (and we knew that anyway ahead of time) why give up the pp deal so easily?
-
write that down
Ah, but the journey IS the adventure, even if you just wind up back home :icon_biggrin:
I've found self biased keeps the flavor, but leaves a lot of loud out, my current PP is a clubman running 23W, if it was fixed, it would be around 40+ fwiw
-
Why not try two 6V6s and if that's still too loud try two 6AQ5s or 6BM8s? Just because 6L6s are too loud (and we knew that anyway ahead of time) why give up the pp deal so easily?
The 6V6s will be too loud at the operating conditions necessary to stay clean.
...and I'm most concerned about the other smaller tubes not being able to handle the big signal V in
The wet rig will have a lot more audio information on it so I'll want a pretty big window to run it through....for bandwiff
And the idea of more second harmonic is intriguing.
I had to try the 6L6s at lower volume just to see, but like Ed said, and you guys all know.
If you aint creamin' em, you aint hearin' em....(write that down too...in fact I think I'll add that as my avatar mantra)
Anyone ever done fixed bias SE, or can point me to an example?
-
Here's a discussion: http://music-electronics-forum.com/t4922/ (http://music-electronics-forum.com/t4922/)
The tube won't care about bias method. I assume you'll build for max output = 10W for SE 6L6. Otherwise just check the tube charts. Per tube charts: g1 wants -18V with 350V plate 250V screen. The bias circuit can be sourced from a bias tap off the PT; or tapped off the B+ rail. Then divide down to (-)bias voltage. Per Doug's Library page it's useful to use a bias adjust pot, at least temporarily, to fine tune bias voltage vs. tube current.
BUT, note that it's a cute trick to get 350V plate AND 250V screen. This will require a voltage divider or a separate PT tap or winding. This brings to mind Edcor who may already have such a creature available if you contact them. (Note that at 250 plate volts, the screen is also 250V, but that yields only 6.5W output.)
However I put a 6L6 in my VibroChamp > 10W Hammond 125DSE OT: plate 375V; screen 381V. 320Ω Cathode resistance yields +25V on the cathode, for 27W plate dissipation. 40% of that computes to an estimated 10W output. It works fine. You could duplicate that with fixed bias at 350 plate volts. That's my effective plate voltage after subtracting cathode voltage (375 - 25 = 350).
-
Just try a AC10 power section. Basically 2, EL84's running low volts.
It will not swamp your KT88 SE and it is a very dynamic touch sensitive circuit. I did not want to mention anything specific, but give it a try.
I find it necessary to consider the combined wattage. For instance I have mentioned my mini-stack which is sort of a 5c1 modified champ and a GA6 Gibson. The gibson is the wet amp and both use 10" paper cone Alnico 15 watt speakers. One speaker is not ribbed and I get a good Wet from the 5C1 and the ribbed one I have for the Gibson.
Now I am only able to get 4 clean watts from each amp, but I can still be too loud if I am playing a 3 piece in a tavern. I used Parallel EL84's in the gibson circuit which changes things and gives me sustain and feedback if I want.
When I use the AC15 with the Princeton I am running 3 speakers, 2 10's in the princeton and 1 12 in the AC15. I have used this setup to play in a 20,000 sq foot facility and still couldn't open them up all the way, but they were churning well tho. :icon_biggrin:
As long as you are able to run your dry KT88 amp and maintain a good tone, you will fine because you are planning to keep it running with the wet amp as well, right?
What I am saying is if I use a great sounding amp for my main tone and add an effects amp it can easily be a Solid State amp and sound great. I am not suggesting you use a Solid State amp, but you could.
You will get it, guaranteed!
-
hey that makes me feel good :) someone else suggesting the EL84 heheh. (mine was way early in the thread though and maybe not as related to the status now)
~Phil
-
"Not all those who wander are lost"
J.R.R. Tolkien
"Major full up, I've always played every amp I've ever had full up, because rock and roll is supposed to be played loud."
Ritchie Blackmore
-
> use the 'line' in, which looks to me like that creates a 1.5K input impedance ... Why would you want to knock down the incoming signal that much?
The power amp *seems* to be switchable into a basic though lame instrument amp. Input sensitivity is not great, there's no real tone control, but it will play from a well-strummed guitar or bass. May be killer with a pedal-board adjusted for generally hot outputs.
This Tri-gizmo keeps slamming 300V tubes into clipping; that's its thing. So it is basically 100 Volt signals. A thousand times more than an instrument input should get. If you do, you will distort in the power amp, not the Tri-whatsit; so why have the Tri?
So there's a ton of loss in both the Tri's output section and this power-amp's input to waste-off the difference.
> ...and doesn't that create an input condition that is opposite of what you would want for proper impedance matching?
Matching is only to optimize power delivery from weak or costly (for their power) sources. If you have to save-up for a month to buy one tube, you match.
Here we have too many tubes in a very generous circuit. Power available is very high. Not for any "system" or "impedance" reason, but just cuz they like the sound of 12AX7 slamming on 350V supply.
-
hey that makes me feel good :) someone else suggesting the EL84 heheh. (mine was way early in the thread though and maybe not as related to the status now)
The el84 is the last tube you'd choose if you want to keep things anywhere near clean above a bedroom volume.
-
PRR,
Do you think that my technique of using an AU7 as the input driver makes more sense than std. AX7?
And can you confirm my logic of setting the bias point at -6V so it will be able to take a 12v p-p signal in before clipping?
Am I getting my interpretation of the load line and input headroom correct?
I'm thinking that if I use a single AU7 stage into SE 6L6 that might do it and will allow less power amp overdrive (?)...will I swing enough signal through to the 6L6 grid to make it shine tonally?
I'm trying to allow each piece to operate in some imaginary (but aurally apparent) "sweet spot"
-
"Not all those who wander are lost"
J.R.R. Tolkien
"Major full up, I've always played every amp I've ever had full up, because rock and roll is supposed to be played loud."
Ritchie Blackmore
:BangHead: "Serenity now!" George Castanza
-
hey that makes me feel good :) someone else suggesting the EL84 heheh. (mine was way early in the thread though and maybe not as related to the status now)
The el84 is the last tube you'd choose if you want to keep things anywhere near clean above a bedroom volume.
Why? If he's mentioning he's already overpowering the 88 based amp, at the level he needs with 2x6L6, it seems to me he wants more tube tone, but at lower volume, which means a tube or P-P tubes that output lower wattage with the same parameters otherwise no? That way he gets the real tube sound he's looking for but it doesn't come out so loud...
I maybe am just misunderstanding the use case completely, I've been following this thread a ton and seem to be completely off base every time... sorry heh.
~Phil
-
Why? If he's mentioning he's already overpowering the 88 based amp, at the level he needs with 2x6L6, it seems to me he wants more tube tone, but at lower volume, which means a tube or P-P tubes that output lower wattage with the same parameters otherwise no? That way he gets the real tube sound he's looking for but it doesn't come out so loud...
Yes, more tube tone at lower volume....but also more throughput headroom
In my interpretation of "headroom", I'm comparing input signal to the tube's output and it's ability to stay clean.
What jojo is saying (if I may speak for you Sir) is that there are 'better' output tube choices and operating conditions that will facilitate the transfer of clean input to clean output, and allow the big signal that comes from the preamp and then gets amplified by the driving stage of the power amp to not overload those output tubes.
If nothing else, I would consider some higher plate voltages on the EL84s to try to manufacture more "headroom",,,but to be honest I'm seriously leaning back towards SE 6L6, 440V'ish plates, fixed bias, single (or paralleled) AU7 driver,,,bam
-
What jojo is saying (if I may speak for you Sir) is that there are 'better' output tube choices and operating conditions that will facilitate the transfer of clean input to clean output, and allow the big signal that comes from the preamp and then gets amplified by the driving stage of the power amp to not overload those output tubes.
Surely you may my good man as that's close enough without mentioning the simple fact of keeping neutral/transparent tone coloration. I'm a tad skeptical when all is said and done if the SE 6L6 is going to have the amount of clean output you're wanting and looking for? No absolute way of knowing until you build it and compare. I can't know as I've not done the optimized SE '88 yet.
-
Gotcha
~Phil
-
LESS gain = greater input threshold. consider data below:
12AU7350V = B+
4mA = IB
Vbias = -6V
Ra = 47K
Rk = 1.5K
Rload = 220K
Vout ~ 110V pk.
Input threshold ~ 19.2V with Rk NOT bypassed AV=is 9
Input threshold ~ 12.9V Rk with Rk bypassed AV=14
given the parameters of bias for any working bias condition, there is a maximum Vout that the the triode can swing into a given load. AV given in the RC chats is calculated at <5% sine distortion measured at output into a specified load: this correlates to AV = output V / input V with less 5% or less sine distortion.
if you bypass Rk, then AV increases, therefore input V must decrease if output V and load do not. RC charts assume you will operate with Rk bypassed. Values of Rk given are for corner rolloff at 50Hz. and the Cc cap is usually calculated for corner of high rolloff at 15KHz.
summary: remove bypass cap to improve input threshold.
you could also add a pair of zener diodes at the input to limit input swing. if you want to limit input to 15V then use a pair of 15V diodes.
--pete
-
hey that makes me feel good :) someone else suggesting the EL84 heheh. (mine was way early in the thread though and maybe not as related to the status now)
The el84 is the last tube you'd choose if you want to keep things anywhere near clean above a bedroom volume.
I was thinking the same thing about the PP 6AQ5 also suggested for the clean amp.
The Bogen K10 PA amp modification I got from DummyLoad gets dirty really quick.
Even with the NFB loop fully engaged, I can't get to 3 on volume without some dirt.
This has a 6AU6 feeding a 12AX7 before the output section.
Maybe the 6AQ5 could stay clean longer with a different preamp circuit?
I'm not to sure about that though because the 6AQ5 is basically a 6V6 in a 7 pin bottle.
From my very limited experience, the only tube I have that can seem to stay clean is the 6L6.
-
summary: remove bypass cap to improve input threshold.
I knew that. :rolleyes:
Cc removal surgery scheduled for 5:01 PM EST
-
Operation was a complete success...
The removal of that cap sweetened up the front end just enough that the cleans are now much closer to staying clean and there was NO adverse effect. The amp, as expected, is also slightly quieter.
You have to love when you do something that is such an obvious improvement that there is no reason to question it any further...that appears to be the coup de grace for the tweaking of that specific amp and now I can take that information and use it as I try to get something a little different out of the SE 6L6
Since the driver stages are already set up on the board I'll just try removing BOTH stage caps in an attempt to drive the 6L6 clean'ish.
If that's still too much, the next step will be to un-parallel the 2nd stage....and somewhere in there I believe is the solution.
I'll report back once I'm up and running.
-
Alright, so I had the bright idea to stop putzing around on the board and just wing it.
So I swapped out the KT88 for a 6L6GC in that amp and here were the numbers under those conditions:
405VDC a-k
25 VDC across 300ohm rk
79mA @ 32W pdiss
So I wont get away that easily, but I should be able to just raise rk and wrap this up.
It did sound slightly different, but I didn't run it very long under those conditions,,,just long enough to say "ok, that's close enough for R-N-R"
I guess I could put a couple different rk values in this next one and make it switchable for KT88/EL34/6L6
I tried that same experiment with an EL34 and the numbers were:
415V a-k
25V across 300R
79mA @ 33W pdiss
I'm gonna hate to wrap this thread up,,but I'm sure you guys are getting tired of me.
And I have to get back to actually playing guitar, so the sooner I get hooked up the sooner I cant start hackin' it up again.
-
The final piece of the puzzle will be a speaker for the dry side that will complement and counteract the EM12 on the wet side.
I have a bunch of stuff here that I have accumulated so I will be selling off some speakers to get to where I need to be price wise.
I tried some speakers at "The NY Amp Show" this past year at AES's booth (they had a very cool switchable 4x12 cab there)
The one that stood out to me the most was the Jensen Blackbird....it was darker, fuller, warmer, sweeter and seemed more toneful than most
I have never spent big money on speakers, and used a $400 4x12 Vintage 30 cab for 10 years, so I have no other decent speaker experience to speak of
Speakers I have ruled out so far: (all Celestion)
Greenback 12M (cant handle the 88 output- kind of sloppy - want/need tighter bass)
G12H-30 (too crispy - harsh)
Vintage 30 (confirmed that I just don't like that voicing anymore - nasally mid humped)\
I probably need something a little darker to counteract the KT88 sting (?)
-
When talking Celestion you have to be more accurate in saying what you're using since it's easily misleading. I believe you have the anniversary g12H right? This is not the same as a Heritage 55Hz G12H 30w. This has a lot of bass and punchy w/ a nice upper end and overall a lot of harmonic structure even at lower volumes you want to play at. Scumback are some of favs right now especially the PVC, but Weber & Warehouse are also really good. Many to choose from but you must take into account the break-in. And BTW the cream is excellent. If you don't want too bright then Tone Tubby is worth checking out. These need to be played at a certain power level to get their mojo out of them. And if that's the case they are awesome, they just don't have quite the harmonics & overtones like Celestion and not a bedroom amp speaker. (in my experience of course) remember the Peavey cab with 2 12 70-80's? They have the H1777 cones and sound really good, and different when in a different cab. Or when open back...just an FYI
-
That's why 2- KT88s aint gonna happen,,,because loping around isn't the same as force feeding electrons through an OT, .........
Depends on how big/small the OT is.
-
Ok, I thought I was following this thread pretty close - off and on. However, it is apparent I am not or I am missing something. The triaxis is a stereo out. So I take it you will be inserting some sort of effects rack in the loop? So you will have true stereo - Chorus, echo, verb, flange, whatever? If my assumption is correct, my question is: Have you ever sent a true stereo effect to two different amps to actually hear the result? I've done it several times with two different amps and in my humble opinion, it sounds like crap (except for maybe some crazy pan echos). The tonal and feel differences between the two different amps seems to completely screw up the effect to my ears. When I connected the same setup up to two of the same amps or SS stereo PA, it sounded great. If you are banging away with just the triaxis and you want a combined feel of two amps, great. Mono effects, great. Or some sort of A/B, great. Otherwise, you might be disappointed. Again, this is my very humble opinion. I'd like to hear Ed's opinion, since he has the same preamp on several amps? You may want to actually try the two out together if you can breadboard your second design - just to make sure you like the result.
I thought the discussion was what tube/style of amp to build two of, not two DIFERENT amps. Sorry. :BangHead:
Jim
-
Jimbob, I do not personally own a Triaxis, but I am familiar. I have a couple of others, my favorite being the Rocktron Voodoo Valve. I agree that Rock i loud and should be felt as well as heard, problem with this is most club owners these days DO NOT ALLOW volumes above the point where their patrons cannot socialize easily. If it were up to me it would be like the late 70's when I used a 100 Watt Marshall and an 8, 10's cab wide open.
Here is the problem today with the low volumes and using only 1 amp. If you are playing mostly or all covers you have to be able distort, flang, chorus, phase, pitch shift, echo..................
To me whenever you add a modulation effect it changes the basic tone, that is why when recording duplicating the original track and adding effects to the duped track maintains the single tone and still allows for the effect. Now I have never done what SG is doing because I use the 2 amps, preamp and all. I simply keep the processor output much lower. With both cabinets or a single stereo cab if you keep them close together and 'Mix" your effects in the air this allows me to have my cake and eat it too.
An example of a cover song is the best way I can explain. Candlebox tune Far Behind. Amp 1 churning enough to growl EL84's and amp 2 running a touch of delay and lot of verb and some chorus as well. The "wet" amp will not clean up when you roll back as it is clean already. When rolled back the Dry amp will be clean and fall to the background opening up room for the intro and verse of the song.
When the song gets a little heavier all I have to do is roll up and the "Dry" amp comes to the front because a dry signal cuts easier. Then it is solo time so Dry gets boosted and so does the Bass, Drums and Vocal. Still there is all those wet effects, but you cannot hear them very much. In this particular song I have 4 different basic tones and my hands of course (yes, I can play the song with thumb and fingers).
Never does it feel like I am playing through a pedal and listening through a headphone amp! If you get those speakers too far apart it can sound strange, Now some would say they can do this same thing with one amp and I will tell you that you are making assumptions. If effects did not change the overall tone of your amp there would be no such thing as an Effects loop. And that is all I am really doing is hitting the front of the amp because to me it sounds much better because even with a loop and I have played some amps with great loops. This is also much simpler while playing.
Think about it. I can play Candlebox and Rinestone Cowboy and only change the volume knob on the guitar.
Man how I loved the old days leaving a club all fired up because I just had a great band melt my face, but you don't see large speakers for home use anymore. Jim, just face it. Today's audiences' are a bunch of wimps, but if you want to get the local gig you gota play nicely. The drunk driving laws killed the mega club and Grunge killed rock.
-
I thought the discussion was what tube/style of amp to build two of, not two DIFERENT amps. Sorry. :BangHead:
Well, I discovered as we went along that 2 different amps would hopefully give me a different texture, and that is more important than having 2 of the same amps. The KT88 is a bit overpowering and is full of character...2 of them might be too much.
So after much back and forth and idea tossing, I've decided to go SE KT88 dry plus SE 6L6 wet.
The FX unit I will be using uses the Triaxis as an insert, which is a fancy way of saying that my signal goes into the TC G System first and then feeds the Triaxis through an insert loop that I have to setup to be ALWAYS ON...
One of the 2 Triaxis outputs goes back to the G system to complete the insert loop, and gets effected, and then mono feeds the 6L6 power amp through it's own 1x12"
The other Triaxis out feeds the KT88 amp directly and acts as a mono dry tone into it's own 1x12"
The G system routes the signal that way so that pre-preamp effects go in front and post-preamp (time based) effects go after the insert (Triaxis)
So anything that is pre-preamp will also effect my "dry" signal, which is ok with me.
I have had the same problem as you and most other guys who have tried to run rack systems in stereo, and so-forth...it never sounds great.
I believe that the root of my problem was that I had a huge signal feeding a power amp and could never get the power amp cranked up enough to get the tone of the power tubes to come out. Part of that problem, as I see it, is that the power amp itself was setup with too much gain and an inability to handle a big input signal voltage.
I think that by using a 12AU7 as the input driver stages we have created an amp that is less likely to distort and more likely to be able to push the power tubes and get a better overall tone at a volume that wont be injuring anyone. I will be able to run the preamp at an optimal level and not have to knock the signal down so far just so I'm not hammering the front end of the power amp. In turn I will able to turn the power amp up higher, and because I have limited my output volume by keeping it to one SE amp per side, I should be able to run them both at a point that will get decent results.
We shall see.
The wet side will be run through an Eminence EM12 (which is full range'y like an EVM12L) in a "Thiele" ported cab
The dry side is yet to be determined but I'm leaning towards the Jensen Blackbird because it is the best sounding speaker that I have heard in person.
(jojo, I did like the clips I heard of the Cream, I just cant get over the low end character of the Blackbird...I've never seen a guitar speaker with that big of a low end hump, and when you hear it, it sounds full and rich)
The point is to have 2 different sounding outputs that I will blend together and they should fill each other out.
-
Here is the problem today with the low volumes and using only 1 amp. If you are playing mostly or all covers you have to be able distort, flang, chorus, phase, pitch shift, echo..................
Think about it. I can play Candlebox and Rinestone Cowboy
...and that's exactly what I'll be trying to do.
This is my best solution for attempting to be a jukebox style cover player who can pull up 10-20 different sounds and have them fairly close to sounding like the record....with all volumes adjusted and multiple effects switched in and out without looking like a tap dancing fool.
But also making myself happy by retaining a powerful TUBE TONE
-
Got it! I was hung up on true stereo effects sounding good. You guys have something completely different in mind. Don't get me wrong, my volume is everything is meant very tongue in cheek. I don't even enjoy getting my hair pinned back any more - unless I'm the one doing it! My wife and I went to see The Alan Parsons Project Saturday night. We were off to the side second row so we were under the PA. It was really enjoyable until the last few songs when the PA guy got ballsy. Still a fantastic show. Speaking of which, one of the guitarists had an iPad on the mic stand that he was switching his effects on his amp with. Bluetooth? Is that possible now? Don't make fun, but I've still got my trusty coiled cord.....
Candlebox and Glen Campbell!!! :l2:
Jim
-
BTW, the lead guitar player for APP was using a newer Marshall half stack (the one with two rows of knobs...) and was doing a tap dance for effects through the songs. They also had a nice plexiglass sound barrier in front of the cabinet. Sounded really good. The rest of the guitar players were using small Fenders - unblocked. When I saw them a few years ago at Epcot outdoors he had two Hughes and Kettner half stacks and the other guys had single half stacks. I guess they taylor for the venue. Not enough plexiglass to go around :dontknow: :icon_biggrin:
Jim