Thebes,
There are certain tasks which one must have a scope to troubleshoot. Analog AC waveform signal tracing is one of them very near the top of the list. Sure you might get lucky and fix it with just a meter, heck you might just shake a loose connection on one of the tube sockets and fix it.
For noise and hum issues it is best to work from the output back towards the input. But for no signal or weak signal I prefer the "halfway" approach. Apply an input signal and there is no or little output. Pick the spot in your estimation (from schematics hopefully) that is "halfway" between input and output. Is there signal there?
1) No, then you know it is closer to the input so go "halfway" again towards the input.
Or 2)Yes there was signal "halfway" you know the problem is closer to the output so go "halfway" again towards the output.
etc......etc.......etc.......