Another bias question

[6B4G]

I am able to bias one side at 700mA with a -68v
The best I can get on the other side is 345mA by droping to -45v at -55v
I get just over 200mV.
I just can't see what I've done, I've checked and checked.
PLEASE help me. Yellow_Light_Colorz_PDT_13

[TomMcNally]

Check the diode and make sure the polarity is correct
and make sure it's not shorted (bad) also check all
components in the bias circuit for proper values.
You may have an incorrect resistor. Measure them
if the color codes are not clear.

... tom

[6B4G]

Hi Tom and thanks
All have been checked twice over.
The only thing I can think of is, could it be the 10k pot?
Even though I measured it and it seems ok.

[TomMcNally]

I would doubt the pot is bad ...

Since you have a good working amplifier to compare to,
the best way to troubleshoot is to take both resistance
readings from one to the other (with the amp off) and
voltage readings (carefully) with them on ... there
has to be a simple solution. Make sure all of the
bias-related resistors on the driver board are of the
correct value also ... measure them and compare
good amp to bad amp.

... tom

[6B4G]

Thanks Tom
I'll get on with it.

[Ty_Bower]

Have you tried swapping the power tubes (KT88 or 6550) between the side that works, and the side that doesn't?

[6B4G]

I did change the full set and no difference.
I did find that a measurement between diode and the 1k (4.7k) to the wipe gave me a 1.7k reading on the good amp, but the bad one gave me a 5k reading.
I tested the 1k and it gave me a 1024 ohm (1k) correct reading, it is as if the pot can’t see it.
I’m going to get another pot in the next couple of days and change it.

[6B4G]

Sorry for the delay had to go out of town.

[6B4G]

I found fault on the driver board. Now the amps are up and running. The sound is great, smooth and warm with lots of power behind them.
Thank you for the help.

Regards
6B4G