[morzh]

Andrew

I can see this is turning into some "I am gonna try bunch of unsystemathized moves, so keep telling me in what direction to run".

Again: get methodical about it. Can you get lucky? - yes you can, but you won't learn anything and you might not get lucky.

Get a meter.
Measure voltages.
Clean the switch a proper way (try that Fader Lube thing, Deoxit).

Check continuity of various coils.

But get methodical.


PS. In tube schematics resistors most of the time are loaded with what becomes open circuits when powered down. Those biases to the grids, loads and such - they often meet a tube electrode (grid, anode) on one end and when powered down this end is disconnected.
So, tube-based circuits lend themselves that much better to in-circuit resistor measurements than say transistor or any semiconductor curcuits do.
So when checking resistors, it is often enough to just place the meter leads across the resistor and see if it is higher value by more than 20%.
There are some exceptions, but they are few.