• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Boyuu A10 with EL34B, 6P3P, 6CA7

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kronzilla,

Triode mode gives the best damping factor possible for a non global negative feedback circuit. It does have negative feedback (direct plate to screen feedback), but it also gives the lowest power out.

Ultra Linear mode has a little negative feedback (plate to screen tap). It has more power out than triode mode, but less damping factor than triode mode.

Pentodes have no damping without using negative feedback around them. They potentially give the most power out. You must have known that, so you used a 82k feedback resistor when you went to pentode mode.

It is good that you were able to use global negative feedback, the original output transformers, and did not have oscillations.

Post a schematic sometime for those who want to duplicate your modifications of the Boyuu A10 amp.
 
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