• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Fixed bias potentiometer

I also use 10 turn pots with fixed R's either end so that Vbias can't be adjusted to 0v. I also put fixed R's,usually 1m between wiper and end tag/s.

I use nail varnish to secure the shaft on Bourns pots and RS still sell the locking nuts you mention. come to think of it I may have one spare, drop us a PM if interested.

Andy.