Radio City Products model 704 RF signal generator

[radiotvnut]

Here's a circa '46-'47 Radio City Products model 704 RF signal generator that I dug out of the stash. It's been here for years and I think I got it as part of a bunch of stuff that came from a fellow collector who had passed away.

Looking at it from the outside, it was obvious that someone had replaced the power cord and the RF output jack. Once opened, I found that the electrolytic filter capacitors had been replaced; but, the old wax paper capacitors were still in place. I replaced the old capacitors and one resistor that was out of tolerance. One day, I'll probably replace the RF out jack that someone installed with a modern BNC connector. I checked the output by tuning the generator to 455 KC and checked it against a known good somewhat later model transistor radio and found that the generator is out of calibration. It also appears that someone has been messing with the trimmer capacitors.

Now, I suppose I need to invest in a frequency counter in order to get it back in calibration. I would use a digitally tuned radio, if I owned one. It's hard to believe that I have hundreds of radios over here; but, not one of them is digitally tuned.

Also, does anyone know of where I can get a copy of the manual?

[bob91343]

That isn't a BNC; it's called UHF or SO-239.

You can calibrate it against another generator that you trust by listening to the beat between them. You also can use local AM stations as markers.

I am sure it's simplicity itself; the company wasn't known for sophistication. So you probably have an oscillator tube in a Hartley or Colpitts configuration, an unregulated power supply, and a simple oscillator for modulation. Maybe three tubes in all.

My Precision E-200 is very accurate. It's also for sale.