Stereo SE KT88 power amps for live rig

[SILVERGUN]

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   
 
 

       
 

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.
 

[jojokeo]

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.

[jjasilli]

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).

[pompeiisneaks]

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

[Ritchie200]

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....   Ok, you have come this far, Grasshopper....  It's time to burn the KT88 brand onto your forearms and complete your training.

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

[SILVERGUN]

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.
 
 

[SILVERGUN]

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.
 
 

[SILVERGUN]

....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.

[shooter]

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

[jojokeo]

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 ...
(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. 


Shooter - good "stash" of info there   

[Ritchie200]

 

Jim

[Ritchie200]

BTW, how loud do you think two 6L6's are going to be?   Why not use a tube that at least sounds good!

Jim

[Willabe]

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, ........

                             

[PRR]

> 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.

[Ritchie200]

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.

Raving lunatic.....HA!
Jim

[Willabe]

  Not helping Jimbob. 

[SILVERGUN]

Jim

Not helping Jimbob. 

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?

[SILVERGUN]

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

I've been using an abbreviated version of that technique and never thought to change frequencies during the tests...thanks for mentioning

[Willabe]

Yes,,, now hush up and let the adults finish talking.

Come on, really? 

[SILVERGUN]

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?

[jjasilli]

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. 

[pompeiisneaks]

> 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
 

~Phil

[Ed_Chambley]

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.

[SILVERGUN]

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.

[SILVERGUN]

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.

[jojokeo]

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
 
! No longer available

[Ed_Chambley]

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.

[SILVERGUN]

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

[jojokeo]

...although I won't be utilizing the insert loops because I have no pedals that I am attached to.

  But you haven't tried one of mine?  (sorry for the shameless plug  )

[SILVERGUN]

   But you haven't tried one of mine?  (sorry for the shameless plug  )

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 

[mresistor]

SG     "Justin Beiber"    aaackk!   LOL
 

[jjasilli]

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


It would be interesting to know the voltage output of the Triaxis' sweet-spot.

[SILVERGUN]

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

[Ritchie200]

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

[jjasilli]

FWIW it seems the Triaxis is supposed to feed the Mesa Boogie 2-90.  Schematic here:  http://schematicheaven.net/mesaboogie.html


Anyway that's how Mesa Boogie handled the input stage fed by the Triaxis.

[shooter]

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?

[jojokeo]

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...

[SILVERGUN]

FWIW it seems the Triaxis is supposed to feed the Mesa Boogie 2-90.  Schematic here:  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?
 
 

[SILVERGUN]

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

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)

[jojokeo]

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?

[shooter]

write that down

Ah, but the journey IS the adventure, even if you just wind up back home
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

[SILVERGUN]

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?

[jjasilli]

Here's a discussion:  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).

[Ed_Chambley]

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.


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!

[pompeiisneaks]

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

[Ritchie200]

"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

[PRR]

> 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.

[jojokeo]

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.

[SILVERGUN]

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"

[jojokeo]

"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

   "Serenity now!" George Castanza