On Jul 20, 3:45*pm, "Even Steven" wrote:
* * *I'm working on a Hallicrafters SX-25 Super Defiant. It uses two 6F6
tubes in push pull in the audio
circuit. Boy do they get hot! Too hot to touch. If my finger lingers I'd
have an awful blister in less than a second. Is this normal? I've checked
the tube voltages and they seem to be where they should be...280 VDC on
plate, 6 volts on heater, 18 volts on cathode. Does anyone have any ideas
about how to help these things run cooler?

* * Steve

I "tube roll" various 6K6's, 6F6's and 6V6's through vintage radios
(checking the bias, of course, but not 6L6's - too big!) and they all
run very hot - far too hot to touch! The metal ones seem worse for
burns.
But, -18 volts seems a bit high for a class AB P-P stage bias... no
need for class A. There might be a positive g1 - you should check
that the audio coupling cap from the previous stage is good. It
should permit no more than, say, +5 mV on the o/p tube g1.
Regardless, I always change this cap for a modern, high voltage, 0.05
uF.
Cheers,
Roger