I really think the issue is the voltage, it's at the very top edge of the spec, and outside of some tubes by about 100V...
the only tru way would be to drop the voltage into a zone that would allow you to roll other tubes.
as you know if you do this, a few resistors will have to be changed
and a diffrent transformer. will it change the sound. I dont know.....
on the web sites schematics it shows a lower voltage, not the 420v or so that you have to start out with....
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