36 Watt EL34 Superlite TMB

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colossal
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Re: 36 Watt EL34 Superlite TMB

Postby colossal » Tue 09/03/19 10:16 am

crgfrench wrote:
Tue 09/03/19 8:25 am
...so, since Josh's tail resistor is 15k, this amp might benefit from the 82k load resistor. Perhaps?
Possibly. Josh's posted voltages indicate a good DC balance, but the AC balance is another story. EL34s require a little more of a push than EL84s too.
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Re: 36 Watt EL34 Superlite TMB

Postby JMPGuitars » Tue 09/03/19 10:27 am

crgfrench wrote:
Tue 09/03/19 9:16 am
Sonically, probably would sound about the same either way.

To make a long story short, "nevermind".
Exactly! The intrigue of any theoretical discussion has to outweigh my laziness. Since any potential reward is likely unnoticeable, I'll let somebody else experiment if they want to. ;)
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Re: 36 Watt EL34 Superlite TMB

Postby crgfrench » Tue 09/03/19 10:37 am

I realize this may seem OCD but you could optimize it with a Dale 68.1k and a Dale 22.1k in series, for a nearly perfect balance, just sayin'...
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Re: 36 Watt EL34 Superlite TMB

Postby colossal » Tue 09/03/19 10:49 am

Dumble used a trimmer pot in the middle of the pair of PI plate loads and attached B+ to the wiper. The Inverting side might get 91k and balance trimmer at 10k. The AC balance is set by dialing the trimmer and using a scope with a target of about 6V difference being desirable. Some imbalance is desirable for tonal consideration. The 18W PI is more center biased than a Plexi PI too and that will change the sound as well.
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Re: 36 Watt EL34 Superlite TMB

Postby JMPGuitars » Tue 09/03/19 11:09 am

I have a difference of 2 VDC at the plates, all else matching. I could swap the tube and probably get 10 or 15V difference at the plates, or an exact VDC match.

Theory is great, but tube variance is reality. If you want to tweak that to make your OCD happy, you'll want to do it like colossal said re: dumble, and rebias every time you change the tube. I could see some people being entertained by that...but I'd rather play if I ever get any free time. ;)
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Re: 36 Watt EL34 Superlite TMB

Postby crgfrench » Tue 09/03/19 12:37 pm

colossal wrote:
Tue 09/03/19 10:49 am
...The AC balance is set by dialing the trimmer and using a scope with a target of about 6V difference being desirable...
I would take a very similar approach:
The AC balance is set by dialing the trimmer and using a stratocaster with a target of the juiciest tone and sweetest sustain being desirable...
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Re: 36 Watt EL34 Superlite TMB

Postby colossal » Tue 09/03/19 1:21 pm

crgfrench wrote:
Sat 08/31/19 11:41 am
Josh how did you decide on the 1kuF value of the output cathode bypass cap?
I am bumping this as I'm interested as well. Josh, did you try A/Bing the stock cap and a 1kuF or just go with the big one to get more of the fixed bias stiffness right from the start?
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Re: 36 Watt EL34 Superlite TMB

Postby JMPGuitars » Tue 09/03/19 1:51 pm

colossal wrote:
Tue 09/03/19 1:21 pm
crgfrench wrote:
Sat 08/31/19 11:41 am
Josh how did you decide on the 1kuF value of the output cathode bypass cap?
I am bumping this as I'm interested as well. Josh, did you try A/Bing the stock cap and a 1kuF or just go with the big one to get more of the fixed bias stiffness right from the start?
I've built many superlites. I've built them with 100, 250, 1000, and 2200uF caps. They all sound good, but I think I remember liking the 1000 more... Who knows, it's been a long time since I thought much about that cap. I actually drew that circuit a couple years ago, and I'm not getting any younger. ;)

But also keep in mind that my build has a 5AR4 tube rectifier, and I have a dropping resistor on the B+, so it's not going to sound too stiff anyway. If anything I miiiiight have been thinking about how it affects the bottom end.

Thanks,
Josh
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Re: 36 Watt EL34 Superlite TMB

Postby colossal » Tue 09/03/19 6:13 pm

JMPGuitars wrote:
Tue 09/03/19 1:51 pm
I've built many superlites. I've built them with 100, 250, 1000, and 2200uF caps. They all sound good, but I think I remember liking the 1000 more... Who knows, it's been a long time since I thought much about that cap.
I know I tried a 1000uF cap once, but it was so long ago I can't quite remember its effects. I want to say I remember it affecting the feel of the amp and I preferred the stock 47uF cap better. Oh, and I meant stock 18W, not a Superlite...
JMPGuitars wrote:
Tue 09/03/19 1:51 pm
I actually drew that circuit a couple years ago, and I'm not getting any younger. ;)
Man, none of us are {=[
JMPGuitars wrote:
Tue 09/03/19 1:51 pm
But also keep in mind that my build has a 5AR4 tube rectifier, and I have a dropping resistor on the B+, so it's not going to sound too stiff anyway. If anything I miiiiight have been thinking about how it affects the bottom end.

Thanks,
Josh
For sure. The screen supply dropping resistor will dump some voltage on big transients, giving some great sag and compression. That's why we love these amps! Very easy under the fingers and they sustain forever.
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Re: 36 Watt EL34 Superlite TMB

Postby JMPGuitars » Fri 09/06/19 2:40 pm

I was playing earlier on a Lite 2b(ish) variant today, with a 250uF cap on the cathode. The amp sounded a little farty playing in the lower register, and especially with my looper pedal playing backing tracks. I rebiased the amp, swapped the 250uF for a 1000uF cathode cap, and it sings now.
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