Coincident with several recent threads here about these ancient instruments, I very recently acquired my first VTVM. It's a working Simpson 311, a bit battered on the outside but apparently working well on the inside. Got it for $5 at a local recycled-goods store! The plastic meter cover has been broken on one side, and rather crudely, yet cleverly repaired by cutting a piece of a plastic box to fit over it. Ugly, but it works.
It appears it might be a military version: the case looks regular, but both tubes inside are JAN (Joint Army-Navy) types. Plus the D cell is an olive-drab issue! (Plus I picked up another meter with this one at the same place, an even more ancient (1939) Weston "Volt-Ohmmeter" in a Bakelite case, a Signal Corps issue according to the nameplate on top, both with hand-written tags by the same person. This one, unfortunately, seems to be non-working, with a cracked glass meter face, but it looks so cool!)
It's a way cool piece of test equipment, in my view: I've always wanted one, ever since I was a kid. Only had to wait ... lessee ... many decades, anyhow, to get it.
But of course it's not working perfectly. I've only tested low DC voltages so far. A 9-volt battery reads 11-something volts. So obviously it needs some adjustment. I see several adjustment pots inside (which I am not going to touch until I know what I'm doing).
Questions (and I'm especially hoping Dean Huster might take an interest and reply here):
1. Anyone know where I can get a manual and schematic for this, hopefully for free? I see them being sold all over the place, so this might not be possible. At least I need a service manual for it.
2. It came with part of a "probe". Does the probe contain any resistors or anything else other than just a straight-through conductor? Can I make one myself? I can certainly pick up a BNC connector locally. The ground connector just has an alligator clip on it; this too is easily made with just a banana plug.
3. If it seems to work OK, is it likely that it actually is working OK? I don't have any good references to test it against, other than zeners or 78xx regulators.
It appears it might be a military version: the case looks regular, but both tubes inside are JAN (Joint Army-Navy) types. Plus the D cell is an olive-drab issue! (Plus I picked up another meter with this one at the same place, an even more ancient (1939) Weston "Volt-Ohmmeter" in a Bakelite case, a Signal Corps issue according to the nameplate on top, both with hand-written tags by the same person. This one, unfortunately, seems to be non-working, with a cracked glass meter face, but it looks so cool!)
It's a way cool piece of test equipment, in my view: I've always wanted one, ever since I was a kid. Only had to wait ... lessee ... many decades, anyhow, to get it.
But of course it's not working perfectly. I've only tested low DC voltages so far. A 9-volt battery reads 11-something volts. So obviously it needs some adjustment. I see several adjustment pots inside (which I am not going to touch until I know what I'm doing).
Questions (and I'm especially hoping Dean Huster might take an interest and reply here):
1. Anyone know where I can get a manual and schematic for this, hopefully for free? I see them being sold all over the place, so this might not be possible. At least I need a service manual for it.
2. It came with part of a "probe". Does the probe contain any resistors or anything else other than just a straight-through conductor? Can I make one myself? I can certainly pick up a BNC connector locally. The ground connector just has an alligator clip on it; this too is easily made with just a banana plug.
3. If it seems to work OK, is it likely that it actually is working OK? I don't have any good references to test it against, other than zeners or 78xx regulators.