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

[Reece]

This will be a fun project. In the rear chassis photo I see a mica across the grid leak, which needs to be added to the schematic. A perusal of old catalogs from that era shows cabinets and blank front panels available for those that had the few extra bucks. I think 01A's will work fine in all positions. On stronger stations it will operate a speaker with moderate volume using both stages of AF. It's an example of a pretty good project some guy probably thought over a long time, planning it, looking in catalogs, finally ordering all the stuff, having fun building it, and then fascinated, logging in distant stations. There was many a bleary-eyed morning after he was up fishing for DX all night.

[PaulOF]

Oops yes. Forgot to draw that cap in. It's an aerovox, making it, I think, the only component in the set made by a company still in existence.

I can't tell you how well I remember finding projects in the radio and electronics magazines in the early 1960's, digging out the Allied Radio catalog and adding up the cost of components, and then saving up until I could afford what I couldn't salvage.

Here's a couple of ads for the Uncle Sam tuning coil. They say you can send off for plans. Maybe that's how your set was made.

http://books.google.com/books?id=DCk...ectric&f=false

http://books.google.com/books?id=rCk...ectric&f=false

[Reece]

I did the same with the Allied catalog in the fifties and sixties, saving up pennies to buy components and scrounging the rest from junked sets. In your set, Hammarlund of course existed until fairly late, as did Rauland in Chicago, making sets and picture tubes. Rauland built some Silvertone stuff for Sears.

[bob91343]

I don't see any problem. Just mail to the address in the magazine and get the info.

[Sandy G]

You saved an ANCIENT veteran from an uncertain fate...Somethin' to be said for that...

[mstaton]

A page down from the second ad, there is an ad for those Rauland audio xformers

[dieseljeep]

Originally Posted by PaulOF

Oops yes. Forgot to draw that cap in. It's an aerovox, making it, I think, the only component in the set made by a company still in existence.

Allen Bradley is still in business!

[7"estatdef]

Hi Paul
Looks like you've got your self a nice old regen set. Great set to have a lot of fun with. A regen set is really sensitive you be able to log in some real DX once you get her working.
Have fun w/it
Terry N3GTE

[PaulOF]

Well, the new interstage cores arrived a couple days ago from AES, so I opened up the first transformer. Disassembly was pleasingly easy, the D's just slid out



The size of the new core was perfect. With a little work I managed to get all the D's back in.



The second one went just as smoothly. So i powered it up without any tubes installed to check voltages. The plate voltages of the two amplifiers were fine, but there was no voltage on the detector or any of the filaments.

The problem with the filaments turned out to be the switch. I took it apart, which was surprisingly easy. It has a bistable mechanical contraption built around a pair of cones joined base to base with a spring around them. Attached to this is a bit of copper that bridges the two connections. Here it is first closed, then open.





Open it read "infinite" ohms and closed a couple meg ohms. I compeletly disassembled it and polished the contacts and now I have filament voltage.

Turns out that the reason that there was nothing on the detector plate was that the "tickler" coil was open. I liked the pretty blue wire on it, but I decided to rewind it.

Before:


and after:


The detritus is the remnants of the Barge Cement that I used to stabilize the coil as I wound it. It will clean off fairly easily.

So I put it back together, checked the voltages again, plugged in the tubes and was greeted by ... silence. This surprised me a little because I am quite close to the 50,000 watt clear channel KYW and I can almost receive that by sticking an antenna into a cabbage.

So I dragged out the signal generator. AF applied to the detector grid sounded in the speaker, so the new transformers and both audio sections are ok. Hooked up the scope to the detector grid and wrapped the rf output around the antenna. Messing with the tuning capacitor, I could see the modulated rf peaking on the grid and, better, hear the AF coming out of the speaker. No sign of oscillation though.

I did discover, however, that all of the binding post connections are, um, tenuous. I could make it stop working altogether by just bumping various wires. I think I need to clean and retighten every one of them. Also get a better ground and antenna hooked up. I already re-soldered all of the connections to the phone jacks, all of which were brittle and looked like cold joints. I wonder if the crystalline structure had changed over the years. I am also wondering if in spite of all my care to prevent it I managed to install the tickler backwards so that it is supplying negative instead of positive feedback. I'll check that tomorrow after I clean and retighten all those binding posts.

Paul

[Reece]

Great progress, waiting for the update. You may not need much of an antenna. Some regens are happy with ten or twenty feet strung around the room. Too much antenna can load them down and swamp them so they won't regen. You can also use a variable cap in series with the connection to your outdoor antenna to cut back on the damping effect of the big antenna. Sometimes just a "gimmick" capacitor was used to connect to the antenna: just two pieces of insulated wire twisted together for three or four twists, no direct connection.

Are you sure all your tubes are good? Sometimes old tubes that light may lose contact from the internal wire to the pins and need the old solder cleaned out and resoldered.

[PaulOF]

Thanks for the ideas Reese. I "borrowed" the tubes from my working Crosley regen, so I think they are ok. I need to buy a few more 01a's so I have a little reserve.
Paul

[PaulOF]

Tightened all of the wire connections, then took another gander at the schematic. Once I connected the earth ground (bottom of the antenna primary) to the signal ground (a+ b- connection) stations started coming in nicely. Not as much volume as I would like from the speaker, but should be fine if I can find my hi impedance headphones.
Paul

[Reece]

Great, she sings again! What are you using for a speaker? You could try a modern PM speaker with any single-ended output transformer you have around.