What is the voltage To bias a marantz 8b?

I heard there’s this thing called a browser. Apparently you type letters in and out pops the answer. In fact, a whole bunch of answers! The one I think you are looking for is 50 mA   https://www.thetubestore.com/lib/thetubestore/schematics/Marantz/Marantz-8-B-Owners-Manual.pdf

Thank you, I see that it is 50mA... i don’t know how to convert that to voltage. Can you help?

You need help reading the manual? Okay. As the marantz owner's manual explains, tube bias is adjusted to 50 mA. There is no reference to voltage. Got it?

I took a look at a "partial" but fairly complete service manual for the 8B, which can be downloaded from hifiengine.com if you register there or are already registered there.

I think that you might be able to get **roughly** into the right ballpark by adjusting the bias pots for the nominal control grid and plate voltages which are specified in the document. Obviously that is not an ideal procedure, as the resulting bias current will depend on the parameters of the specific tubes, among other variables. But FWIW those values are as follows, measured with respect to chassis and at a line voltage of 117 VAC (adjust the following numbers by the ratio of your actual line voltage to 117) , and with inputs shorted. (If you don’t have RCA shorting plugs on hand, a number of eBay sellers offer them at very modest prices):

Control grid of EL34s (pin 5): minus 36 volts
Plate of EL34s (pin 3): 420 volts

A better procedure, of course, would be to temporarily connect a milliammeter in place of the defective bias meter. If you choose to do that, though, BE VERY CAREFUL. The terminals of the meter are at 435 volts relative to chassis ground!!!

Hope that helps. Regards,
-- Al