[morzh]

OK, it worked, but there is that hum issue.

I traced it to the balancing resistors from the 47 tube's filament to GND.

   

They are supposed to be 10 ohm (the sch shows that).
Removing the GND center removes the hum almost completely, but, of course, it is not right as the filament should be referenced to GND.

When I desoldered one resistor, it showed 5 Ohm from the center, and the one I did not desolder was 10 Ohm from the same point.
Upon desoldering it, both became 5 Ohm. The fact it was soldered by one end could not change that.

So, I am hesitant to solder it back as I suspect there is some issue in the resistive wire going to the lugs.
I have ordered 10 ohm resistors and will solder them instead tomorrow.