The more clues we have, the closer we can come to determining what it might be.

As I said earlier, it's decently put together.

Here's a link to more bottom pictures that show the connections to the 1 henry choke. They are the two orange leads.

Best I can tell, that choke is in parallel with the big variable cap.

I may try to process the pictures and upload at some point, but I'm too tired at the moment from replacing the 7F8 socket fasteners on an SX-43.

https://drive.google.com/drive/mobile/folders/0B0DqApsPCs8CaVp6S3VJNXhKeHM

http://www.daycounter.com/Calculators/L ... ator.phtml



Frequency:
0.008330
(MHz)
Capacitance:
365
(pF)
Inductance:
1.00e+9
(nH)

You are correct

So...
the evidence is mounting that you have yourself an audio oscillator of some sort.

Perhaps,further googling of homebrew audio oscillators will turn up a circuit. However, like a homebrew piece I posted about last year, the tubes that are in there may not be what it was designed for, although they would certainly be suitable for such a circuit. I'm just saying in your research, don't assume they're necessarily correct, but they're a starting point at least.

I have searched a bit, to no avail currently, and tested the output screws on the chassis. Two of the output screws have 120v across them and the other two have no discernible voltage across them.

That's a pretty high voltage to have on exposed terminals like that. Please be carefulness!

About the only way forward is to trace out the circuit and draw up a schematic, which hopefully you or someone you know can do.

Just plug it in to a variac and slowly power it up, while checking the terminal strips with a scope to see what if any waveform is present there. One of them is likely an output.

It's also a very simple device and wouldn't take more than a few minutes to draw the schematic by hand using the tube basing information which is readily available.

It appears to be a receiver for listening to VLF frequencies ,possibly ground waves .

Hopefully this weekend I'll be able to draw up a schematic. Thanks for the reply.

I've drawn up a schematic and written out my oscilloscope findings. If needed, I can clarify anything that confuses anybody. Here is a link to the schematic image. https://drive.google.com/folderview?id= ... EtoWVRldmM

I did what you suggested, minus the Variac. I don't have one of those at the moment. Check out my post with the link.

I made a schematic and I don't think it's an audio oscillator. Check out my recent reply

Here's a video of the oscilloscope and me moving the controls. https://drive.google.com/file/d/0BxJKkd ... p=drivesdk

I saw your schematic and notes right away, but I'm afraid I'll have to ponder on it for a bit when I have more time and earlier in the day when the synapses are firing more fully.

Hopefully others will jump in and solve the puzzle as folks around here are so good at doing.

it , is some form of a grounded grid amp , most most likely needs an ant balun , for it to work .

Could you elaborate a bit please? Like I said I'm pretty new to this stuff.

https://en.wikipedia.org/wiki/Balun

That is a low frequency ground grid amp or radio , and need a balun or input transfomer for it to operate, . that is why it won't pass a signal and have 140 volts to ground at the input .

The tuning circuit is in the plate circuit , and has to have a resistor across the input or a balun to complete the the cathode circuit to ground .

The tuning cap and the inductor across it values will tell us the frequency range it is supposed to tune .

So the terminals with 120vdc across them are the input?

Yes that is the input and needs to be terminated properly , to operate correctly .

http://www.hans-egebo.dk/Tutorial/amplifiers.htm

see grounded grid amp