silverface twin bias question

stskeith · Posted: Mon Jul 28, 2008 2:54 am Post subject: silverface twin bias question

Hey all,

I have one of our silverface twins that i have just installed a quad matched set of 6L6's into as the amp quite humming quite badly.

I have also installed 4 x 1r/1w resistors from pin 8 to ground, and here lies my question......

i am see across these

V7 40ma
V8 45ma
V9 41ma
V10 19ma???????

obviously amp is still humming, any sugestions ??

Keith

tw001_tw · Posted: Mon Jul 28, 2008 5:49 am Post subject:

What I would do is take voltage reading on all the pins, (v7-v10) and compare them
to your troublesome V10. (that 19mA just won't do!) This would determine
if its the tube or the amp.
If its the amp, then work from the schematic from the worse offending pin
on v10 till you find your problem. Did I explain that ok?
-tw

stskeith · Posted: Tue Jul 29, 2008 10:22 pm Post subject:

yes thanks,

It is definatly the amp and not the Valve, have tried new valves allready, also, it is not the first time that this amp has acted up like this, will try like you say to chase back from the worst offending pin on V10 and see what gives.

Thanks
Keith