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Old 08-15-2018, 02:43 AM
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Atwater Kent Model 20 No. 7570

I like Atwater Kent TRF sets. The electronics are simple, the restorations are straightforward, and they're very attractive (to me). My oldest is a Model 30--a one-dial, battery, tabletop set.
Looking for something unique, I found a promising three-dial set on eBay for a reasonable price.



The set had a full set of five UX '01A tubes, of which three tested good. The only thing missing was a metal collar for the antenna hole in the back of the cabinet.

After pulling the chassis, I found two wire-wound grid resistors open, one AF transformer open, and the single bypass condenser open. I managed to repair the resistors, found an AF transformer replacement in a box of spare parts, and the single bypass was a paper condenser that I would have rebuilt anyway. Beyond that, all components were reasonably close to the original specifications. I have a Flickr album showing details of the restoration: https://flic.kr/s/aHsmov3ZfS


I finished restoring the chassis.




The first time I powered it up I could only find one station, but I could get that signal anywhere on the dial. The next day I tried again after switching some tubes and realigning the dials, and I could get a couple more stations. On my third try I started to get the hang of it--juggling two filament rheostats and the three tuning dials I could find all the local stations which I usually receive, but it takes a lot of adjustments to get decent audio quality.

I'm moving on to cabinet restoration, but I'd appreciate any suggestions on the electronics to make the radio even more wonderful that it is now. These are my current parts values and the voltage readings from the first time I powered up.



Thanks for looking,
Henry.
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Old 08-15-2018, 07:02 PM
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Very nice restoration job, you should be proud.
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Old 08-16-2018, 02:33 AM
Titan1a Titan1a is offline
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You did a great job. It looks nice and probably plays better than new. I'd get rid of that moving-iron speaker though.
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Old 08-28-2018, 03:46 PM
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Cabinet Finished, Power Supply Built

Finished the Model 20 cabinet a couple of weeks ago.





The most difficult issue was replicating the missing metal trim (collar) for the ground port at the back of the set. The only thing I could figure out was to make a plaster impression and epoxy putty cast. The original trim is thin stamped or pressed metal, so the epoxy duplicate is very delicate. It took me two full days to get it to look right.





With the radio restoration complete, I went on to part II of the project: So far I'd powered the set with an ARBE III. Now I need a dedicated power supply. Three years ago I made a power supply for an Atwater Kent Model 30 by stuffing an Antique Electronic Supply Battery Eliminator Kit into a Bosch Nobattry Case. Then, when they were on sale, I bought two more K-101A kits for future projects. I used all of my miraculous abilities to make this power supply look vintage-ish and Atwater Kent-ish.





I shoe-horned a K-101A kit into a box that was too narrow and too short. To compound the crowding issue, I added a vintage toggle switch (from an AK42), six voltage terminals (from a Radiola 28 A/C conversion kit), and an on/off indicator light (don't know where the red lens came from).





Incidentally, in response to the comment about the speaker: That's just a utility speaker I use during restoration. This set will be paired with an AK Model H horn. I'll post a family photo when I get them together.

QUESTION: On voltage terminals for battery or battery eliminator connections, one or two terminals are brass with brass screws. In the Radiola 28 set of nine terminals, two are brass and seven are brass with plating plating and steel screws. Which terminals should be brass, and why?

- Henry
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Old 08-28-2018, 04:48 PM
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Looks great! I have a couple of those, and need to source an extra dial. Actually, need to do my research to see what that dial should say, first...
Nice job on the chassis/knobs, and the wood.
What was your out-of-pocket on the build-up of the power supply?
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Old 08-28-2018, 05:38 PM
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The wood box was $14 and the K-100A kit was about $45 when I bought it. I had everything else. What kind of dial do you need? The 0-100 tuning dials for the Model 20, 30, and 37 appear identical--except possibly the Bakelite color varies. I have a spare Model 42 tuning dial, but the numbers are much larger than the earlier models.
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Old 08-28-2018, 05:50 PM
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If you ID the transformer part number and the part numbers of the solid state parts you could probably make your own kits for a fraction the price ordering from mouser, digikey or the like...If you substituted those solderable perf board PCBs (that most electronics hobby shops/sites sell) or a few 5 pin terminal strips for those dopey individual terminal lugs that kit uses you could probably build it a lot smaller.
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Old 08-29-2018, 12:35 AM
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Make vs. Buy

I have one more K-101A kit for a future project. If I anticipated doing two or more power supplies beyond the kit I have, then I would buy components: 12 Zener diodes, transformer, 2 bridge rectifiers, two transistors, one thermistor, an IC voltage regulator, and a heat sink. Everything else I've got--even some perf board I got when Radio Shack was going out of business.

I used the wood box because the shape was so similar to the radio cabinet, and I wanted something smaller and lighter than the Bosch Nobattry metal case that I'm using with the AK Model 30. That thing weighed about 20 pounds when it was full of the original components, and it's still too heavy when it's totally empty. Here's a size comparison:




And here's the "Happy Family" photo with the Model H speaker:



Anybody know why one or two terminals on a vintage battery eliminator have brass screws? (This sounds like a joke, but it's a real question).

Forty photos of this project: https://flic.kr/s/aHsmov3ZfS

- Henry
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Old 08-29-2018, 01:34 AM
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I heard that these radios where quite performant for theyr days. It this true?
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Old 08-29-2018, 02:34 AM
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My radio memories only go back to the early 1950's, but I think that it would have been quite satisfying in 1926 to have a radio which a room full of people could comfortably listen to. I'm happy with the performance of this set, but it would have been better when it was new. Then again, the technology was advancing so fast that this set was followed by an improved version of the Model 20 in a few weeks after this one was sold.

Here's a link to a relevant cartoon from 1928: https://flic.kr/p/TbVbVs
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