[morzh]

If you use today's DMM to measure voltages you will have higher readings as the Avometers of the days of yore (I bought me recently a Weston) had much lower per volt impedance and so loaded the circuitry which ion case of tubes is fairly high impedance, so the readings were lower.

I specifically bought practically a mint military meter that has a switch between 1kOhms/Volt and 20kOhm/volt. The latter was calledc ""supersensitive" and is probably the one mostly suitable.
1Kohm/Volt is good for alighning tube testers - some procedures explicitly ask for this per-volt resistance.

But in most cases a modern DMM will at least give you an idea if the stage is working correctly - after all, today's DMM's readings are in fact "truer" and you need an old meter just not to thing about the difference.