Biasing questions (hopefully simple . . .)

[WienerDog]

I have a Vox AC50CP2 combo, which uses two EL34 power tubes. The amp has bias test points and two adjustment pots (one for each tube).

I just got a new set of 6CA7 tubes I would like to try. For each tube, the plate current is measured at 52.4 mA. The transconductance for each tube is about 6900.

Based on these numbers, what readings should I be looking to get from the amp's bias test points?

Also, when measuring from the test points, should I set my multi-meter to DCV or mA?

[Blue Strat]

Those are test readings on the boxes and are used for matching the tubes. They have nothing to do with the readings you should set the bias for.

To really zero in, you should know the plate voltage of the amp so you/we can calculate the idle current you should set the tubes at.

In general, there's never a case where 35mA won't work or be safe.

If the amp is like every other one with test points, you set the meter for mV DC.

Before installing the new tubes take readings on the old ones and experiment with changing the bias. Set it to the lowest point possible before installing your new tubes.

Good luck.