DC-3 Bias resistors

[scotteggshell]

Hi can anyone tell me if I am correct in my assumption that I can replace the 33k in the bias supply with a pot to control the bias voltage, or would that give me too little adjustment ?

Maybe I need to vary one of the 220k's on each pair ?

From this drawing:

http://www.schematicheaven.com/boogieamps/boogie_dual_caliber_dc3.pdf

Has anyone done a Bias mod for DC-3 that would like to help out ?

Thanx
Scott

 

[wizard333]

Look at the phase inverter; see where it has the 2.3V coming in from the bias supply? If you change the bias, you need to
1) Measure the voltage there at the cathode of the phase inverter
2) Once you add that adjustable bias, make sure you're still getting that voltage at the cathode of the phase inverter
3) If you arent, you need to adjust the resistor going to the cathode of the phase inverter. Might even want to add a pot there to.

Thats the oddest phase inverter design I've seen in an amp, and I can't begin to tell you why they used it. The 5 and 10 use a standard long tailed pair like nearly every other amp in existence since the early '60s. Why they went with that design on the 3, no idea.