have to fix some Voltohmyst VTVMs

[DavGoodlin]

The GO-TO meter to use on tube equipment, to measure the voltages found on our schematics, is a Vacuum Tube Voltmeter or VTVM.

Famed publisher John F. Rider developed a meter with Co-worker Jack Avins using a bridge circuit, calling it the Voltohmyst, then selling his business and a few patents to RCA in mid-1939.

Recently, a friend asked me if I had one for him, so I handed over a RCA-made, Viz-branded WV-98C with its manual, but minus the switchable probe. It needed a bit of work as do several others I have accumulated recently. So I thought a thread would be appropriate. I have four Heathkits, so maybe a separate thread is needed since I saw neither HK or RCAs, only some on Hickok VTVMs, in this forum since 2010.

I found a WV-97 in a pile of other junk that showed up, and the needle on the meter was stuck. I figured it was done for, but I took the meter out and I was able to free it up after backing off and re-tightening the front and back pivot nuts. Checking the movement coil on the 20K range of my Craftsman DMM, it supplied enough current to push the needle to 40% of full scale. Now to replace the battery with a 10 yr. lithium and the selenium rectifier, electrolytic and paper caps and see if I can calibrate it.

The second VTVM is a WV-77E I just picked up for $10 at Kutztown swap last week. It is in much nicer condition and a bit different. I also have a manual for it, which covers troubleshooting.

One thing I noticed without getting in deeper is that the WV-97 has two 6AL5 tubes and the WV-77 has one 6AL5.

How about your experiences with these or similar VTVM's?