Vintage Kearfott / Ballantine VTVM?

[deafen]

Picked this guy up for a song, because it's got that 1kv range (and it looks cool). Dates from 1958 based on the tube date codes. It's branded Kearfott, but I think it's OEM by Ballantine - the meter is branded by them, and it came with a paper schematic for Ballantine 310A. It's not a 310A though, because that one doesn't have a 1kv range. It's also got an unusual miniature 5-pin plug-in rectifier with two 310 diodes in a plastic cylinder - also branded Ballantine.

There's an identical one up on eBay, but otherwise I can't find any reference to this device. Kearfott seems to be known for aircraft gauges, not test equipment. It doesn't match with any Ballantine model that I can find.

Anybody seen this before? Any tips or links to reference materials? I'm guessing the circuit is identical to the 310A except the range selector. Once I figure out how to expose the innards, I'll have a better idea.

(Picture attachments aren't working for some reason, ok try to add them later)

[bdunham7]

Can you link the one on eBay?  I can't find it.

How much (or little) does it resemble the 314?

[deafen]

Here's the one on eBay:

https://www.ebay.com/itm/Vintage-Kearfott-AC-Voltmeter-Vacuum-Tube-Aircraft-Military-/284505717430

[bdunham7]

That looks a lot like a Ballantine 314.  You mentioned the custom rectifier thingy--does your unit have this in place of the selenium rectifier in the other photos or is it somewhere else?

https://www.radiomuseum.org/r/ballantine_wide_band_electronic_vol.html

[deafen]

It's definitely the same chassis, but there are a few differences:

• The 314A has one more tube. Looks like another 5654 maybe? This unit has a capped off BNC connector labeled "AC input" in its place.
• This unit has an incandescent bulb between the two 0A2 tubes. Could be part of a stabilizing circuit, but could also just be a power indicator - there's no indicator lamp on the front face, and while this would only shine out through the side louvers, I guess that might be better than nothing?
• The 314A can only do 1kv with a special probe (which I'm assuming is just a 10:1 voltage divider).
  

It's still got the selenium rectifier and the 6X4. On closer examination, it's not a rectifier - the diodes are in series. It's got pins connected to the anode of the first, the junction, and the cathode of the second. The 310A schematic shows that arrangement as part of the meter circuit.

The more I look at it, the more I think it might be basically a 310A with an additional divider for the 1kV range. The 310A schematic that came inside it does seem to match up well from early investigation.