Rick Ralston wrote:

What is the +/- % of deviation that can be applied to heaters on say 12ax7
tubes. I am rebuilding a small single ended 7695 amp and after I got the
heater supply wired the voltage on the 12ax7's is in the 13 volt range. Any
help would be greatly appreciated.



About 5%. Use a 5 or 6 ohm resistor in series with the heater
(assuming 12.6V hookup) to drop the excess 1V. This also
lets the tube heat up with less stress on its heater.