Bias query

[hylaphone]

Hi folks - in this bias circuit, how would one go about increasing output to around -50V?
I am unfamiliar with the use of transistors here
Thanks--

[loudthud]

Increase R55 to 7.13K.

[J M Fahey]

.............

[hylaphone]

OK thanks. Are Q1 and Q1 working as regulators or something?

[Jazz P Bass]

OK thanks. Are Q1 and Q1 working as regulators or something?

Yes. It appears to be a series pass regulator.
The divider network R56/ R55 (with the help of R57) sets the base voltage of Q2/ PNP transistor.

The two transistors are set up as a darlington pair to pass a higher current (as opposed to simply one transistor)

[Enzo]

Before you start changing too much, go to R57 and see how much voltage is there. That is the highest voltage available in this circuit. If the 50v caps there are well specified, you may not even HAVE 50v to adjust up to.

[Chuck H]

.............

Can I sig this?

[Dave H]

Before you start changing too much, go to R57 and see how much voltage is there. That is the highest voltage available in this circuit. If the 50v caps there are well specified, you may not even HAVE 50v to adjust up to.

Yeah, it looks like the input voltage should be about -84V but it doesn't make sense to have C31,C32 at 50V and C30 at 150V. It should be the other way around.

[hylaphone]

All are correct here - the caps are 150V rated - looks like they have the V/MFD backwards on the schematic
Bumped R55 to 8.2K and now have a nice usable range at the bias pots
Thanks for the help!!

[Enzo]

I should have just accepted LT's advice, I seldom have reason to doubt him.

[Dave H]

I seldom have reason to doubt him.

I'll agree with that