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Bingo!
Will look at your PM later, just found out something important (from what I just
read)! When in phono mode, the power supply does not feed the two radio tubes,
so current through R18 is lower, and so the screen voltage on the output tubes
does get higher, increasing cathode current. Also touching the control grid
does induce hum as your whole body, meter, etc. act as a coupling capacitor
to feed hum to the amplifier stage. Doing this to the grid of the previous
stage (6AU6) should induce even louder hum as you now have two tubes
amplifying.
The funny voltages on the 6AU6 tubes: do they remain funny when you set
the switch to radio? If the two channels have different readings, something
is wrong with components... Bye for now.
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