ampage Tube Amps / Music Electronics	For current discussions, please visit Music Electronics Forum.	New: view Recent Searches. New: visit Schematic Hell! The sunn still shines online!

Listen to great tunes streaming live right now!

ampage archive

Vintage threads from the first ten years

previous: jeremy there is probably a resistor b4 tha... -- 9/6/2003 6:57 PM	View Thread

Re: Biasing Crate VFX 5112?

9/6/2003 10:24 PM
John T	Re: Biasing Crate VFX 5112? Jeremy, thanks for your reply. I don't quite understand what you mean by putting a resistor of the same value across the R before the trim pot. That would cut the value in half and make for less voltage drop across the pair, and make it less negative? Seems like that would bias the tubes hotter. I really should have taken a scan of the schematic while I had it, so I could know what the H*ll I'm talking about I thought the current draw was pretty mis-matched too. The tubes were one of the Tube Store's "perfect pairs". Yeah right! So does 25 watts at idle seem way too hot to you? Again, I used the current shunt method which should be pretty accurate IF my meter has a low internal resistance. I looked at the owners manual for my "Yu-Fong" DMM, and it said in current mode the "voltage Burden" is <0.7V That seems insignificant compared to the dynamic R of the plate(?) Anyway, I am a little concerned that I let it go with that much plate dissipation. If I ask him to bring it back for another look he might think I'm incompetent Thanks again. John T.

9/6/2003 10:24 PM

John T

Re: Biasing Crate VFX 5112?

Jeremy, thanks for your reply. I don't quite understand what you mean by putting a resistor of the same value across the R before the trim pot. That would cut the value in half and make for less voltage drop across the pair, and make it less negative? Seems like that would bias the tubes hotter. I really should have taken a scan of the schematic while I had it, so I could know what the H*ll I'm talking about

I thought the current draw was pretty mis-matched too. The tubes were one of the Tube Store's "perfect pairs". Yeah right! So does 25 watts at idle seem way too hot to you? Again, I used the current shunt method which should be pretty accurate IF my meter has a low internal resistance. I looked at the owners manual for my "Yu-Fong" DMM, and it said in current mode the "voltage Burden" is <0.7V That seems insignificant compared to the dynamic R of the plate(?) Anyway, I am a little concerned that I let it go with that much plate dissipation. If I ask him to bring it back for another look he might think I'm incompetent

Thanks again. John T.

Replies:

hasserl So does 25 watts at idle seem wa... -- 9/8/2003 6:09 PM
jeremy That would cut the value in half... -- 9/12/2003 12:50 AM