Monthly Archives: October 2013

Bias points and 10-turn potentiometer

I decided when it comes time to bias this amp I don’t want to have to pull the chassis out. I remember seeing a Komet amp┬ádesigned by the late great amp legend Ken Fischer that had a crazy looking potentiometer knob that looked like a combination lock. With a little research I found out knob is connected to a 10-turn potentiometer. A regular pot turns less than 360 degrees meaning that minute adjustments to bias are hard to make. With the 10-turn, the pot takes 10 rotations to travel through it’s resistance, making it a great pot for adjusting bias. The knob has a concentric dial, and with each turn, the outer ring clicks up or down by a number. It also has a lock on it, so once adjusted it won’t move.

I also drilled holes for banana jack bias points as a lot of companies are doing now. This set up will make biasing the power tubes a cinch.

***Note – I ended up not using this fancy expensive pot because it just stuck too far out the back when I mounted the amp in a standard head cabinet. I ended up using a PEC locking pot that I got from DigiKey***