36 Watt EL34 Superlite TMB

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zaphod_phil
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Re: 36 Watt EL34 Superlite TMB

Post by zaphod_phil »

crgfrench wrote:
Mon 09/02/19 11:35 pm
Josh you might want to consider changing your plate load resistor to pin 1 of the PI to 82k.
I believe the one at pin 6 should stay at 100k but if you use 100k at pin 1 the PI will have unbalanced outputs.

I'm no expert on LTPs, I only build cathodyne, but I am pretty sure you want lower voltage at pin 6 than on pin 1. Because at pin 6 the signal has already been amplified by the first triode. Using 82k will raise the voltage at pin 1 (I believe it should be 5V to 15V higher) which will result in balanced signals from the PI.

I'm not sure why Trinity uses equal 100k load resistors there (Richie Hall's 18W designs also suffer from this error but his 36WTMB is correct. Ian's reference schematic has it wrong too. All of the Wattkins LTPs have this problem too), but Marshall, Soldano, Egnater, Aiken, Huss, Hoffman and Robinette all use 82k & 100k at the PI.

You could also use 68k at pin 1 and 82k at pin 6 to run it hotter but still balanced.

This might all stem from the original schematic derived from Colin Macfarlane's amp, which shows twin 100k resistors here. That could be a mistake.
Once again, that's not a problem, nor a mistake at all! Unless you want a hi-fi amp, of course. :) Having 100k for both PI load resistors gives a slight amount of imbalance, allowing more even-order harmonics to be produced in the power amp for sweeter tones. That's one of the reasons for the Marshall 18W magic. The same logic goes for not using matched power tubes. Note:the 100k/82k combination was introduced be Leo Fender in his misguided quest to make his guitar amps more hi-fi. That error in judgement was then inherited by Marshall, Soldano, Egnater, etc. Since you mentioned Huss, one of Mark Huss' Lite amp designs does use the 100k/68k, as a kind of experimental idea.
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Re: 36 Watt EL34 Superlite TMB

Post by zaphod_phil »

zaphod_phil wrote:
Sat 04/18/20 5:28 pm
crgfrench wrote:
Mon 09/02/19 11:35 pm
Josh you might want to consider changing your plate load resistor to pin 1 of the PI to 82k.
I believe the one at pin 6 should stay at 100k but if you use 100k at pin 1 the PI will have unbalanced outputs.

I'm no expert on LTPs, I only build cathodyne, but I am pretty sure you want lower voltage at pin 6 than on pin 1. Because at pin 6 the signal has already been amplified by the first triode. Using 82k will raise the voltage at pin 1 (I believe it should be 5V to 15V higher) which will result in balanced signals from the PI.

I'm not sure why Trinity uses equal 100k load resistors there (Richie Hall's 18W designs also suffer from this error but his 36WTMB is correct. Ian's reference schematic has it wrong too. All of the Wattkins LTPs have this problem too), but Marshall, Soldano, Egnater, Aiken, Huss, Hoffman and Robinette all use 82k & 100k at the PI.

You could also use 68k at pin 1 and 82k at pin 6 to run it hotter but still balanced.

This might all stem from the original schematic derived from Colin Macfarlane's amp, which shows twin 100k resistors here. That could be a mistake.
Once again, that's not a problem, nor a mistake at all! Unless you want a hi-fi amp, of course. :) Having 100k for both PI load resistors gives a slight amount of imbalance, allowing more even-order harmonics to be produced in the power amp for increased sweetness in the tone. That's one of the reasons for the Marshall 18W magic. The same logic goes for not using matched power tubes. Note:the 100k/82k was introduced be Leo Fender in his misguided quest to make his guitar amps more hi-fi. That error in judgement was then inherited by Marshall, Soldano, Egnater, etc. Since you mentioned Huss, one of Mark Huss' Lite amp designs does use the 100k/68k, purely as a kind of experimental idea to try. As for Trinity, I was a designer/consultant for them. So now you know! :wink:
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Re: 36 Watt EL34 Superlite TMB

Post by JMPGuitars »

What Phil said. ;)
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