Heathkit model V-7A tube voltmeter acting up. Help?
 

Hey all, I have an interesting issue with a little Heathkit V-7A bench meter. Yesterday I got to clean out a long closed TV repair shop and this was one of the pieces of gear I got.

Initial testing showed life, but the Ohms setting does not read as it should. The meter jumps around. I can touch just the positive lead with my finger and the meter will show a reading. The RX selector switch does nothing as well. I figure this needs restoring of sorts but I would like to avoid replacing every single piece in a Heathkit because it won't behave (Doing this to an It28 cap checker at the moment that does everything but check capacitors).


The battery in this meter is shot, but I am not understanding why it needs this battery. Can it work without one or is this the issue?

Sorry if these are dump questions. I've never had a tubed multimeter.

The battery is needed because it supplies the voltage that is placed across the resistor being measured (after being divided between an internal decade resistor and the resistor being tested). The meter actually measures this voltage, and shows it on the non-linear resistance scale.

http://www.angelfire.com/electronic/...ubes/VTVM.html

The operation to measure resistance has two set-up steps
1) with the test leads shorted, adjust the meter zero adjustment
2) with the test leads open, adjust the ohms calibration to read infinite resistance - this is calibrating the reading when the meter sees full battery voltage.

3) connect the external resistor (Rext) to be measured.

The voltage measured is the battery voltage (full scale) times (Rext/(Rext + Rint)) where Rint is the internal decade resistor. The non-linear scale is marked to indicate the value of Rext. For example, if Rext = 333k and Rint = 1M, the voltage measured will be battery times 1/4, so the 1/4 of full scale point is marked as .333 (Megohm); the half-full-scale point is marked 1 (1 Megohm); etc.