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In Reply to: RE: 6N1P posted by Jonesy on January 15, 2023 at 12:27:34
In the amps there are 20 turn variable off set resistors for positive and negative voltage. You need to adjust both to "0" volts in order for the power tubes to bias properly.With all 4 new tubes in either amp they would not allow the voltage to be adjusted from between 5-6 volts to "0".
When we put the old same manufacturer tubes in, both amps would allow for "0" volt adjustments for the circuits.
It is very strange but no other conclusions than the new tubes are the problem.Down side is I have had the tubes for 6+ month and can't find the receipt or any email related to the purchase. I will call VIVA Tubes but, I don't hold out much hope of a refund or receiving a credit toward the Voshkod tubes.
It is a good thing my EE friend is incredibly smart and built and rebuilt many pieces of audio equipment.
Edits: 01/15/23Follow Ups:
I am asking just for giggles. Have you left the tubes in circuit long enough to warm up nicely and/or burn in? I have seen tubes, especially vintage Russian that are out of spec or will not test unless left powered for an extended time. Once they burn in they are fine. Why not try leaving the tubes in circuit for 8 hours or so and see if you can adjust towards your target voltage.
Another other option is to add resistance to get to the voltage you want. You're EE friend should be able to help with that.
No need to throw out the baby with the bath water yet.
That reminds me of certain brands of signal tubes that would never allow me to dial in the DC balance correctly and hence biasing the output tubes. Nothing wrong with them. Just not a good fit in my (40 year old?) but still in use ARC D70.
It may be the same case with the 6n1p.
I came across some medium and high gain 6n1p on the web. I wonder if that would make a difference to making the adjustment. Maybe your tech friend would know and it would help you refine your search.
"I know just enough to get into trouble. But not enough to get out of it."
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