back on this Mesa Triple, power transformer was getting hot enough to fry an egg on, this amp has the option for either 6L6 or EL34 tubes,
RCA receiving manual says heater current for 6L6 is .9 amps, 1.5 amps for EL34
so if the EL34 option was an afterthought by Mesa, and they did not use a bigger transformer,
well, 6 * .9 = 5.4 amps heater current for 6L6
6 * 1.5 = 9 amps for EL34 heaters
this has been an age old problem for rockers wanting to hot rod their Fenders by adding crunch with EL34's,
easy to re-bias but not much you can do for the pwr xfmr,
so we needed to help the pwr xfmr shed some burden , but no room for another 120/6.3 transformer
so we rip out the choke and install a Hammond 166S6, rated for 115/6.3 at 10 amps, should do the job, but...
see that 115 VAC? big trouble, we get 7 volts now on the EL34's,
so we strip off 2 turns from the 28 turn sec, bake and dip, and get 6 volts now, which is a good fix as it keeps this hot chassis a little cooler,
pwr xfmr is now running as cool as a cucumber and the heater xfmr is a bit warmer but not much,
we theorize that the pwr xfmr got so hot that the bias voltage begin to droop enough to cause thermal runaway of one of the tube banks (either side of a P=P circuit will red plate, but usually not both as once the tubes get hot on one side, they hog the current)
problem is now we do not have a screen choke,
solution is use a resistor, this puts control of plate current back inn the hands of a resistor which can be changed to further tame this beast,
and we can use Fender cold bias specs(60% plate disp. bias) to keep things even cooler during set breaks,
here is the amp with the aux xfmr added,
hopefully this will cure the amp, if not we have other issues, like ultra sonic osc. from a channel or two,
if so, we get out the scope and the pico farad caps and get after that also,
ripped out 12 Henry choke with 115 ohms DCR shown next to xfmr