Here is a piece I picked up on the auction site a while back, thinking it might be a fun restoration project. That was not to be. All it needed was batteries.

It is an RCA Test Oscillator, model TMV-97-C, circa 1929. Range is 90 to 25,000 kHz with built in modulator. It is spot on accurate, but the numbers on the vernier are near microscopic, so a magnifier is needed (at least I need one).

It's a beauty; I would love to have just the vernier dial. What circuit does it use? I see an 80 tube, which would be a rectifier, yet you are running it on batteries.

looks like 2 80's??

I never saw an 80 used as an oscillator. I suspect something like a 45. But what is the modulator?

I doubt it's 2 80's but the lettering is worn down to where you cant tell in the pics

Cool oscillator. I believe the tube on the right is a 30. The other other might be a 30 too.

I aways like old test equitment ,look nice and in good shape. its def. a 30 i have a army version of that one from 1945 and it has at least two 30 's in it

Two 30 tubes would do it, one the rf oscillator and one the audio oscillator. So it does need batteries.

Two 30 tubes would do it, one the rf oscillator and one the audio oscillator. So it does need batteries.

I haven't been able to find the official schematic, but you are exactly right.