AT Voltmeter

Sensitive Research Instrument Corp (Singer Metrics or Singer Gertch) made mostly electrostatic voltmeters. I couldn't find anything Sensitive Instruments made that might be RF related. I have no clue what an "AT Voltmeter" might be. The Ballantine 390 is listed as an "A-T Voltmeter" but I don't want to download 38MBytes just to see the catalog.

This looks like the Ballantine version of the same cavity: Kinda looks like the micrometer adjusts a big piston capacitor, and not a RF cavity, but I'm gussing.

I don't think that glass device is an acorn tube. Not tall enough, not enough leads, no filament, and not enough external connections. My guess(tm) would be either a spark gap or a neon lamp protector. There's a number on the bottom of the glass envelope, which might help.

Value? No clue.

More of the same:

Still no clue on what it does. The wooden box makes me think it's part of some test setup. The labels on the connectors in the photo would have been helpful.

This exactly wht it is. The make/model number lead to this page:

and this is what I've got. The little 'acorn tube' is a glass encapsulated thermocouple. It even says '5 mA' on it.

The little 'acorn tube' is a glass encapsulated thermocouple. It even says '5 mA' on it. Thanks!

More info: The Ballentine Model number lead me to this description:

"Attenuator-thermoelectric highfrequency voltmeter" and patent:

-- Paul Hovnanian mailto: snipped-for-privacy@Hovnanian.com

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Nice. It's all in the patent. Apply some RF to one end of the tube. The micrometer controls the capacitive coupling to the thermocouple, which produces enough voltage to move a millivoltmeter. I guess today it would be called a thermal RF power meter or bolometer. The big advantage is that it stays calibrated longer than other schemes of its day (1956).

I have no clue what you might be able to do with it. Rip out the thermocouple and you have a rather precise adjustable capacitor. You might try selling it to someone with a calibration lab or museum of antique secondary calibration instruments.

The link below is to the website of a deceased friend who collected antique electronics. About 2/3 down the page are a number of their early thermocouple based meters, along with a little of the history of Sensitive Research. I have one of the 'Polyranger' meters that he mentions.

Randy Guttery was a US Navy Veteran, and a Broadcast engineer in Meridian Mississippi. He was an excellent electronics tech, as well.

Thanks. Of the test equipment shown, I think I have either used, owned, or still own much of it. If ever get tired of the stuff, I'll open a museum. I've seen some Sensitive Research stuff at various times, but was never into calibration or metrology, so they were of little interest. Thanks much.

The inventors were employees of US National Bureau of Standards and wrote a paper on their invention:

You're welcome. I did some work in a Metrology lab, while at Microdyne. My latest addition to my home shop is a Boonton 9200A digital RF Milivoltmter. It will replace the analog 92B model that I've had for decades. It's too bad that it doesn't have the second channel, or IEEE-488 interface.

The S-R Polyranger had been donated to a Vocational Electronics course. It was given to me, when the school system dropped the course. I was on the Board of Advisers for that course.

Thanks to you and Jeff for the links. I think I've got enough to figure this beast out.

-- Paul Hovnanian mailto: snipped-for-privacy@Hovnanian.com

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