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Old 17th September 2019, 05:02 PM   #11
w5jag is offline w5jag  United States
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The cathode bypass capacitor will affect the stage gain - a bad one will lower it; I'm not sure that the cathode resistor will affect stage gain.

I haven't read the whole thread, but are you assuming the gain imbalance is in the power stage, or have you verified that?

Do you have an oscilloscope or a sensitive ac voltmeter so you can follow ac signal through the amp and see what is happening with it?

edit: for some reason, I see only ONE cathode resistor on your amp. Where is the other one? On the other side of the board? Why? 680 ohms is probably too high for 6L6GC - I would think you want 560 - 510, maybe even 470 ohms ...

edit2: I would also take a close look at the three terminal connector on the side with no visible cathode resistor - it's probably OK, but looking at the picture, it could also be that both ends of the jumper wire are in the same terminal which is not OK; it would leave the screen floating and effect (affect?) the stage gain.
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Old 18th September 2019, 02:41 AM   #12
Tubelab_com is offline Tubelab_com  United States
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IIRC you stated in a different thread that the difference in gain followed the output tubes when they were switched. If that is the case changing every part in the amp will have little effect.


The SSE is a zero feedback design. This means that the gain is largely affected by the characteristics of the tubes themselves. It the amp used a lot of global feedback the gain of the amp is determined mostly by the feedback components, and not the tubes. If your other amp uses feedback, that would explain this behavior.
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