This question is not specifically about Fishers. I was studying the IBBA schematic to try to answer my question since it does what I'm trying to do. I have an amp that has 2 EL84 power tubes in push-pull configuration and they were fixed biased with 2 resistors, both 22K. I wanted to be able to adjust the bias so I replaced the 2 resistors with one 50K trim pot. I connected the pot wiper to the hole at the "bottom" of one of the resistors, and attached one of the side pot leads to the "top" hole of the same resistor. The remaining side pot lead I attached to the "top" hole for the other resistor. This arrangement leaves the "bottom" hole of one of the resistors unoccupied. I believe what I've done is make only 1 tube adjustable because the wiper is attached only to one of the 2 power tubes. Am I correct? If I want to control the bias on both tubes with the one trim pot, do I need to bridge the wiper to the same side of both resistors? Or do I need a second trim pot? Thorne UPDATE: I guess this is one way to go? https://robrobinette.com/Generic_Tube_Amp_Mods.htm#Balanced_Bias_With_Single_Balance_Pot That means I need a "balance pot" as well as the trimmer pot.