Eric, I've found that 5U4's start conducting at 35 volts ac input.
By 50 volts, you are getting fairly high surges, which go down as set starts warming up.
Diodes wil increase voltage too high without added resistance.
The tubes start warming up nicely for me.
On the escutcheon, if you look at the small white dot above that dial, I'd say that escutcheon was added. My guess is it uses the same knob as in schematic.
Bill Cahill
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