What is the voltage To bias a marantz 8b?

Maybe this doesn’t apply to a 8B?

That appears to be the case, based on my examination of the schematic that is provided in the service manual I referred to earlier.  The meter in the 8B measures the bias current directly.  The voltages you referred to for the other amps are presumably the voltages appearing across resistors which are conducting the bias current, those voltages therefore being proportional to the bias current.  The 8B is different.

The only alternatives that occur to me, aside from my earlier suggestions, are to try to find a replacement for the meter, or to get the amp to a good tech.

Good luck.  Regards,
-- Al

A trick I used to use was to dim the light down so the amp is in the dark but you can see what you’re doing. Turn them on with test speakers connected. Have adjustment tool ready and as tubes heat up, adjust bias so that the plates start to glow slightly red. Then adjust back so the red fades away. While it’s not accurate, it will ensure they are biased. Be careful not to let the power tubes glow strongly red as they could fail (spectacularly.) You can tell from the heat generated after 10 mins or so how heavily biased they are. Adjust when warmed up for sound quality ensuring they don't "red plate".

Clever suggestion, @noromance .  I hadn't thought of that technique.  Thanks!

Best regards,
-- Al

Thank you, that’s pretty much what I’ve been doing. I using some old tele’s and just wanted to make sure I don’t have too
much juice on them

Maybe this thing can help

https://www.amazon.com/Nobsound-Current-Probes-Amplifier-Cathode/dp/B0777F8DBK/ref=pd_sbs_267_3/130-...