If you seak maximum output from the tube, you want to be able to adjust Grid 1 voltage to a point where the the tube characteristic curve for that given plate voltage is indicated on the graph.
Ensuring that the cathode resistor is of adequate wattage is another issue, and that its' value is correct (has not shifted from what is indicated in the color bands).
If G2 bias gets too high, the tube will cutoff and clip severly.
The same is true if G1 voltage gets too high.
If G1 voltage is too low, the tube starts to operate in the non linear portion of it's characteristics, and will distort.
For best THD value, adjust operating parameters of the tube to place the G1 voltage (at a "zero signal input") in the center of the performace curve for that tube at your plate voltage that you have.
:Hi, I am restoring two push-pull 6BQ5 tubes amps. Both plate pins (#7) of 6BQ5 are connected on output trans, voltage is 300V. Center tap of output trans is 300V. Grid #2 pins (#9) voltage is 275V. The 6CA4 rectifier tube give 300V and power resistors in serial give 275, 215 and 150V for all circuit. My question is: Can I connect grid #2 to 300V instead of 275V? If yes, output power will be a bit louder? THD will increase or not? Will I have to tweak all circuit or something else? Maybe it's a bad idea to do this?? There is a lot of questions, but I want to be sure!!
:Thanks for all!
:J-F