[Chas]

See:

   

Note this is the output of the schematic provided, there does not appear to be a triode connection.

   

For triode connection characteristics choose from one of the many offered, at least two offer some parameters to work with:

https://frank.pocnet.net/sheets64.html

Look for motorboating problems at the volume control, input to the amp incorrect wire position, bad ground rivets incorrect values of bias components. Bad or wrong volume control... Be sure shields are in place and properly grounded...

There may be a problem with high voltage on the tone control, if not now, in the future. What I often do with this circuit is to double the value of the "tone" cap. For example if it is 0.1mf make it 0.2mf and place one of these caps on each side of the tone control thus taking the high voltage off the control with the net result in capacitance being the same.

Another consideration is that QRM will cause cut-off of the output then the magnetic field collapses creating a very high voltage in the output transformer. The transformer can flash over at the wiring or internal and burn out. If the tone cap(s) have a dv/dt rating they will effectively absorb the destructive pulse. But if the cap is a plain yellow metallized without a Dv/Dt rating the metallizing will become shattered and the cap loose capacity. Successive QRN hits will cause the transformer to fail. Raising the voltage rating of this cap will not work, it is the internal design, can't deal with the pulse. BTW a vibrator buffer cap is good here...

GL

Chas