I recently acquired a RCA Volt Ohmyst Vacuum Tube Voltmeter. It looks like it was made in 1954. There are a few things that need to be fixed and replaced before I can use it.
When I opened it I was shocked to see a battery that was at least forty or fifty years old that was crudely soldered in. The battery leaked out at some point an there is a bunch of dried up battery acid that has made the chassis rust up a bit and killed the Zero Adjust pot. Besides that it is the typical things that need to be taken care with such as recapping the unit and replacing the line cord with a modern polarized cable.
The modifications I plan to perform are adding modern banana jacks and a mini power source to replace the battery since it is only used for the Ohms reading mode.
The meter came with the leather strap but it has seen better days so I might replace it with a military grade nylon strap or go buy a brown leather belt to cut up and replace it.
I didn’t get any probes with it but you can find all over the schematic for them. I may or may not just build the AC and DC switch into the unit or just build a small adapter that I can use pre made modern probes with it so I don’t have to make any.
So first thing is first. Remove rust or stop it with naval jelly and slap on some paint to seal it. Find a 15K ohm linear taper 1/2watt pot. The rest should be easy.
For the battery eliminator circuit I plan to tap into the filament power source. Add a diode, filter cap and a small Buck converter. The circuit should take up as much room as a D cell battery.
Note: The filter cap is going to be around 2200uF. Now I never used a Buck converter so if I can’t get 1.5Volts I’ll just use a Zener diode. This would make the circuit much smaller. Honestly I could be more crude and do this instead.
This could work. I would have to bread board it and give it a try. The diode on the end of the output adds protection and a voltage drop to get around 1.5 volts.
Since I have been getting more tube equipment I guess I should buy a tube tester soon.