Stereo SE KT88 power amps for live rig

[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)

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

[SILVERGUN]

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

[jojokeo]

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.

[pompeiisneaks]

Gotcha

~Phil

[DummyLoad]

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   

[Paul1453]

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.

[SILVERGUN]

summary: remove bypass cap to improve input threshold.

I knew that. 

Cc removal surgery scheduled for 5:01 PM EST

[SILVERGUN]

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.
 

[SILVERGUN]

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.
 

[SILVERGUN]

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 (?)

[jojokeo]

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

[Willabe]

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.

[Ritchie200]

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.

Jim

[Ed_Chambley]

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.

[SILVERGUN]

I thought the discussion was what tube/style of amp to build two of, not two DIFERENT amps.  Sorry.

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.

[SILVERGUN]

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
 
 

[Ritchie200]

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!!!

Jim

[Ritchie200]

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

Jim