ampage Tube Amps / Music Electronics	For current discussions, please visit Music Electronics Forum.

ampage archive

Vintage threads from the first ten years

previous: Casey4s RG,Thanks for the s... -- 6/5/2000 4:21 AM

Re: Runaway Bias

6/5/2000 7:36 AM
Bruce	Re: Runaway Bias Beam forming tubes don't seem to need much signal to go full bore so make sure you aren't trying to "bias out" a simple oscillation. If there is nothing wired or dressed wrong, maybe -42v is not negative enough to hold back a pair of 6550s at 535vdc screen and plate. I'd start by checking for parasitics though and then redo the bias supply and make sure you can swing it down to at least -60vdc. I'd decrease the screen voltage to about 450vdc too. Bruce

6/5/2000 7:36 AM

Bruce

Re: Runaway Bias

Beam forming tubes don't seem to need much signal to go full bore so make sure you aren't trying to "bias out" a simple oscillation.

If there is nothing wired or dressed wrong, maybe
-42v is not negative enough to hold back a pair of 6550s at 535vdc screen and plate.
I'd start by checking for parasitics though and then redo the bias supply and make sure you can swing it down to at least -60vdc.
I'd decrease the screen voltage to about 450vdc too.
Bruce

Replies:

Peter S Casey, I think you need t... -- 6/5/2000 11:42 AM