[NIGHTFALL1970]

If I buy tubes for my amp and preamp as "matched" pairs,  if one tube blows, then do I have to replace both tubes?  Is it a volume difference?

[Lefty052347]

Amps:
Yes and no to tube replacement.  If you have a spare (same type), install it and rebias both channels.  That will match channels.  However, if tubes sharing the same channel are mismatched one of the tubes ends up carrying a bigger load and will wear out sooner.  Depending on how many hours the tubes have been in service, I would either buy a matched pair or a matched quad.  I normally replace the quad in my Ultravalve when one side can no longer be biased to spec.  For me that is about 14 months.  I toss the bad pair and keep the good pair for a spare side.

Preamp
Our current preamp have some feed back so matching the line stage tubes is not required.  You can plug it a spare of the same type without affecting channel balance.  I would replace them with matched pairs anyway.  If you one of our tubed phono sections I would replace them with matched pairs of 12ax7's that exhibit low noise and low microphonics.


Regards,
Dean

[avahifi]

If you are talking about one of our big hybrid amplifiers (Lefty was discussing the Ultravalve or Ultimate 70 all tube amp) then I would suggest a new set of 12AT7 tubes from us ($35.00).

Keep the remaining old good tube as an emergency spare.

If you replace with the same brand as we supplied in an AVA hybrid power amp, you don't need to reset bias.  Bias setting in these big amps is a tricky job not for the amateur!

Regards,

Frank Van Alstine

[NIGHTFALL1970]

I should have mentioned in my original post that I have the AVA Fet Valve 400R amp, the "NEW" Fet Valve preamp, and Fet Valve DAC.  Thanks for your replies.