#vtvm

[magicclam]

It’s quick-build time!

Relatively speaking... this project took me about a week on and off. 

A friend of mine recently gave me a VTVM (Vacuum Tube Volt Meter). I have another one, but it’s in rough shape. This one was clean inside and looked pretty nice outside as well.

However, it has a quarter-inch jack on the front, and most of my probes are banana jack style. I didn’t want to drill holes in the case, or otherwise mess up the VTVM, so I decided to build a little adapter box. 

A while ago I bought some cool scraps of wood from a local place that sells them for a buck a piece. I that pile of scraps was this cool curly-grained wood (Maple maybe?). So I started out by cutting off a chunk from the small board, then cutting that chunk in half with my bandsaw. After cutting a few more small pieces, I drilled holes in what would be the front, back and top, then glued the small pieces together.

Next I stamped some letters on the top. The original probe for the VTVM had a 1meg resistor in series with the DC portion of the probe. So I installed a switch to let me go between a direct connection and a connection that has a 1meg resistor in series with the positive probe.

Lastly I mounted the jacks and made up the quarter-inch plug, soldering everything together underneath.

I’m really happy with how it turned out... now I just need to get the VTVM working and I’ll be good to go!

Stay tuned for who knows what!

[magicclam]

Hey everyone!

So, a few weeks ago I went up to an antique radio show and sale, and in addition to coming home with a few radios (pictures coming soon!) I bought a Solar brand capacitor checker. 

There was a note on it that said it was working just fine, and it came with 2 manuals, which was nice. However... I got it home and it did NOT work just fine. 

Fortunately I have a friend at work who is just as passionate about antique electronics as I am, and on top of that, he has a much deeper knowledge of this stuff (on the theory and design side) than I do. So I brought it in one day and asked him if he could help me figure out why it wasn’t working. Unfortunately, I didn’t get any pictures of the electronics work, but you can see what the unit looks like in the case...

So we spent a few lunch hours (and some text messages in-between) troubleshooting this thing. I replaced some obvious stuff, like some old wax-paper capacitors that were in there, and some resistors that were bad. My friend gave me some suggestions of things to try, and did much of the deeper circuit investigation work to figure out why it wasn’t behaving properly. :)

A few tweaks later, it’s working! In addition to being a capacitor checker, it’s also a VTVM, so it measures resistance, AC and DC and Power Factor (for capacitors). I went through all of the functions this afternoon and everything was behaving as it should. It’s not crazy precise, but it’s good enough for much of what I do.

I learned a lot from this project, still a lot left to learn, but this was a lot of fun, and now I have a working piece of test gear. Next step will be to clean up and restore the case. I’m going to strip the paint off, re-prime and paint it. Then it will look good AND function properly.

Stay tuned for that and other things!

[magicclam]

Quick update...

I got the VTVM that my friend gave me working!

I spent a little time calibrating it yesterday and now it has a place on my bench. Pictures show the little adapter box I made for it... realized I hadn’t showed the equipment it plugs in to.

Stay tuned!

[vxo]

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HP model 400C #VTVM receiving too much WIOD to really make any sense of its readings. #wiod #HewlettPackard

[magicclam]

Updated my Heathkit VTVM (Vacuum tube volt meter). Replaced the 3 old paper capacitors inside with modern equivalents and replaced a pair of resistors with one similar ohm resistor.

This unit it is a model V-1 which is the first VTVM that Heathkit produced, I have no manual or schematic for it and there doesn’t seem to be anything available online. So I really just had to go by the components that were in there already.

I also believe that the unit needs to be calibrated because when I power it on, I cannot zero out the ohm meter and testing a 47ohm resistor just pegs the needle at 0. Might take a look at it a bit today, there are some potentiometers inside that you can adjust. Will have to trace out where they go to try and figure out what they do.

[magictransistor]

The RCA Senior VoltOhmyst WV-97A AC/DC VTVM, Radio Corporation of America, 1953.