bias on express?

[mresistor]

Hello maybe my first post here. Been lurking a long time.

I have an Express "Francesca" clone here on the bench exhibiting bias adjustment that seems abnormal. It has the 220K bias V dropping resistor and an unknown larger black bias pot.
The amp is currently running 6V6 tubes and I can only adjust the bias down to 14w max dissipation. The bias V on the grids is only variable from -25.3v to -34.7v. It seems odd to me that
the bias range of adjustment is so limited. Since I haven't been in one of these amps before I would like to know what the bias range of adjustment is on a normal functioning Express.
Thank you.

[martin manning]

The min (-35V) and the range (~10V) sounds right for the 220k off the HV. Turn the bias spot all the way up and measure it to see if it is 25k to ground. I'd swap the 220k for a 150k to get 10-12V more negative voltage. If you want to try that out, put a 470k across the 220k and you'll get 150k.

[mresistor]

From the wiper to one end of the 47K resistor I get 0 to 20K ohms. So this must be a 20K pot . Is there a pot you would suggest using? Would a 50K pot be OK in this circuit?

[mresistor]

I had a 150K on hand and installed it an was able to get the bias down to 70% max diss for 6V6 tubes.. Thanks for your assistance..

[sluckey]

I use that exact same circuit in most of my stuff, except I do use a 50K pot, mainly because it will give a wider adjustment range.