Re-greetings and new project

[PaulOF]

Kind people,

It's been a couple years since I have been able to put much time into my hobbies, but now that my two year stint as chairman of our faculty senate has come to a close, its time to get a new project underway.

I recently was given this device:


I think its a short wave converter. It has almost nothing in it by way of a label except for individual components. The two coil holders are marked Silver Marshall. As far as I know, they made both radio equipment under their own name and also parts and radios sold under other names as well. I am wondering whether this was a piece of home brew equipment.

The box is not particularly well made, the chassis is a piece of fir with a sheet of aluminum bolted to it. The electronic workmanship is pretty nice.

Inside, it looks like this on the top:



The two tube sockets (five pin) are empty. I'm guessing maybe a 27 and a 24? The empty coil holder has no connections and I suspect was there to hold a different (and now missing) coil for another band.

From the bottom, it looks like this:



Yep, that's a mouldering C-cell soldered in to provide bias for the tetrode.

There is a mystery device over in the lower left hand corner that I am guessing to be a grid leak resistor. Here's a better look at it:



The 100K wire wound resistor in the top view is well identified, as are the three 0.5 uF capacitors. They look nice enough to rate a picture of their own:


The smaller condensers and the coil on the bottom are totally unmarked.

I've traced out the connections on the larger tuning coil on the top. It consists of the obvious winding and a smaller, finer winding

I've made a first pass at puzzling out the schematic. I am not sure about the large coil's connections, and I will want to re-draw it once I better understand what it's up to so the layout matches the function.



So, does this thing ring any bells for any of you? Any help or suggestion any of you can make in terms getting it working would be appreciated.


Thanks,
Paul

[Sandy G]

Wow..That Bad Boi Be OLD !! I'm thinkin' late Twenties-early Thirties..

[Reece]

Time spot is right, Sandy. Yep, it's a homebrew. The guy did pretty well with what he had. He knew to twist the heater leads to cut down on hum. He used a sheet of aluminum for better ground plane shielding but the wood and the flat head wood screws etc. and the off-kilter front panel scream homebrew. I didn't get a chance to scope out the schematic but I'd bet it's a SW converter too.

[init4fun]

Yes , the mystery device is a grid leak resistor , and one other observation is how few rotor and stator plates the tuning capacitor has . It looks like it was intended to tune a narrow slice of frequencies either just above or below the standard broadcast frequencies . I also agree that it's a well constructed home brew and deserves a restoration

[Reece]

The fewer the plates in the tuning capacitor, the higher the frequency, so that would take it into the short-waves, above the broadcast band.