Classic 50 volume reduction

[proaudioguy]

A friend in another state has a classic 50.  Its too loud.  I do not see an adjustable bias.  He is not competent to be inside the amp.  When pulling 2 tubes on a twin and disconnecting 2 speaker, I have always rebiased but I
Never noticed if I needed more negative voltage or less.  I’d like to tell him to pull 2 el84s, and disconnect one short one speaker.  My question is if he would be in danger of too hot a bias (too low neg voltage).


What do you all think?

[shooter]

I wouldn't recommend it, time/money better spent finding someone that can do the work, especially some 'ol guy that's just in it to keep his skills sharp.
Those amps are already problematic, tend to flame-out just because they can 

[stratomaster]

Put a 250k audio pot wired as a voltage divider in an enclosure with 2 jacks. Send that to him and have him place it in the effects loop. He'll now have a master volume control.

Alternatively, a passive volume pedal or an EQ pedal run flat will work with the gain slider being the volume control.