No self control - 20's homebrew

[PaulOF]

I went to Kutztown with every intention of buying a few tubes I need and an extra variac. Successful in both endeavours, but as I was about to leave, I gave into temptation and picked up this for 10 bucks.



With no labels or markings anywhere, I am guessing that it was a homebrew. The workmanship on the cabinet is quite nice making me wonder if the cabinet and faceplate were commercial. Looking into the top, you see:


The nice piano hinge and the inset step for the lid to close into bespeak the quality of the cabinet work. From behind, the insides look like this:



This will be the first "breadboard and binding posts" era radio I have worked on. The tube sockets are Remler type 50's.



It's a bit hard to see here, but the pin holes are nicely labelled F+, F-, P and G. The antenna transformer/tuning coil is marked Uncle Sam Electric Company, an organization I have been able to learn nothing about.





The tuning capacitor by Hammarlund is quite lovely:





two of the rheostats for the filaments are uninteresting, but the third, labelled "Bradleystat Perfect Filament Control" is kind of neat.





The AF interstage xformers are both by Rauland. One (shown) is an R-21 with 5:1 turns ratio. The other an R-12 with 3:1 turns ratio.



Both have open windings, but I have ordered a couple of the replacement cores that AES sells which I suspect will work. I have used one successfully before on a slightly later Crosley. If they don't fit in the shells, I can always hide a couple resistors and a capacitor inside the shell and just take the dead transformer out of the circuit. Here is one of them opened up:



Finally, here is the schematic that I drew from the thing.



It all makes sense. The variable coil inside the antenna transformer seems to be acting as a "tickler" for regenerative detection. One thing that seems a little strange to me is that there is no RF bypass capacitor across the primary of the first AF xformer.

I assumed that all the tubes are 01's or 01A's, but would an 00A be more age appropriate for the detector? I've never messed with one of those.

The three phone jacks provide output directly from the detector, output from the first stage of audio amplification and output from the second stage. I suppose the second AF amplifier could be a 12A or a 71A.

Anyway, I've decided to treat my unstarted projects as a last-in-first-out data structure this summer, and work my way backwards through them starting with this one. I'll post my progress from time to time.
Paul