National SW-54 Thoughts

[Electronic M]

Series string rectifiers typically have a dial lamp heater tap...the heater can go open on either side of the tap. During WWII when replacement tubes were scarce if the section of rect heater in parallel with the dial lamp blew (likely because the dial lamp died first) instead of changing the rect they would install a higher current dial lamp to allow it to soldier on with a poor tube.

If it is AC voltage scale you want to check on your meter just stick the probes into the wall outlet and you should see somewhere between 110 and 130VAC...Just check your positive lead is in the voltage connector and not the current before jamming it in the outlet. The current jacks on a DMM typically have a short (thick 1ohm piece of wire) between them...I killed my first meter by measuring line voltage with the probe in the 10A current jack...the meter leads melted, but the breaker never tripped.

DC voltage I typically check with a 9V battery. Remember to have the meter set to AC voltage if checking heater and DC voltage if checking B+...If you get that backwards you'll get near 0 volt readings.....Some folks prefer to measure voltage with a DC coupled oscilloscope because it will measure AC and DC at the same time.