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.

RDH4 says +/- 10%. That means about 5.7v to 7.1 v for 6.3 v heaters
or 11.4 v to 14.2v for 12.6v heaters.
Getting heater voltages closer to proper working voltage prolongs the tube
life.

But you should be able to make sure its close to 12.6v.

Using some experimentally sized series R between the transformer winding and
heaters can
trim the heater voltage closer to where it ought to be.

The 12AX7 would be better off with rectified heater voltages,
and if there is a 13v winding and you have a bridge, it will give you about 17v
dc at a first filter cap of
say 4,700 uF, and then you will need to have a resistor to drop down to
12.6v to a second cap of another 4,700 uF.
Caps should be rated at 25v, and C1 for an amp of ripple.
If you can make a 12.6v shunt regulator using a power transistor and a
12v zener diode, then the heater voltage will never
exceed 12.6v even when no tubes are in the circuit.
This is very basic electronics, and you should learn how-to-do.

Patrick Turner.