Peavey Triumph60 Adjustable Bias

[rblp]

I would like to add a pot to adjust the bias of a Triumph 60. I'm relatively new to this so I wanted to check to see if I'm on the right track. I was thinking about changing R81 to a 10k resistor and a 50K pot. Will that work?

Thanks
Bryan

[Enzo]

No, it won't.

That resistor has to form a voltage divider with another for the adjustment to do anything. The upper resistor in said voltage divider is R65 over in the power supply, next to F3 and CR14. it is only 470 ohms, so pretty much othign you do with that 10k and 50k will have any effect. Well, if you turn the pot to zero leaving only the 10k, that would reduce the bias voltage about 2 volts. Not enough to matter much.

You need to increase R65 to something like 3k or more. 3.3k is a standard value as is 3.9k. With that change, you r pot and resistor will make sense.

[Enzo]

Oh, and here is a pdf file of the schematic. Maybe a little easier on the downloads, and easier to work with.

[rblp]

Thanks! I appreciate your time looking at this.

Bryan

[rblp]

Enzo,

Thanks again!. It worked. I put a 3.3k in R65 and I had to use a 100k pot for R81. This and some new caps brought that old amp to life.

Bryan