Home Antique Radios 1920s Tim's 1925 Atwater Kent 20 "Big Box"
Tim's 1925 Atwater Kent 20 "Big Box" PDF Print E-mail
Written by Tim Wray   
Monday, 27 March 2006 19:00

Sometime in the timeframe of 1924/1925, my great grandfather, Doyle Wray, purchased an Atwater Kent 20 model 4640 "receiving set", one of the earliest AM broadcast receivers made. It sat in a closet on the family farm from an early unknown date until my father took it out in 2005. My great grandfather passed away in 1955, the year before my father was born, so I assume the radio had been out of use since before then, perhaps even a decade before then (as the radio was 30 years old already at the date of his death!) There was a short time when the farm house fell out of the family in the late 50s (or at least it was used as a rental by the family, not sure...), and the radio remained in the closet during this time. Perhaps, in this time period, the horn speaker for the radio was lost or stolen, or even destroyed. No antenna was in the area either (this set required an external antenna.)

He kept accurate logs on the original provided Atwater Kent log sheets of all the broadcast stations he received. Most all of the original clear-channel stations of the 1920s are included in the logs, almost a "who's who" of old time radio. I did my best to preserve the contents of the logs in an excel spreadsheet, an html save of this document can be viewed here (NOTE: some stations are listed with the wrong city, according to my research. I suppose they were logged incorrectly; they were preserved here for accuracy to coincide with my great grandfather's logs.)

I recall my dad showing me the radio, which had been sitting in his bedroom closet as a kid, when I was probably about 10 years old. I've always had an interest in electronics and radio...I was the kid producing my own "radio shows" in front of a cassette player, with my brother Todd as an audience, when I was as young as 5 or 6 years old. I had disassembled countless radios and even a couple televisions by the time I was 12, and have always been especially fascinated with the idea of restoration...bringing dead electronics back to life again for people to enjoy. Recently, this little bug bit me again, and the old Atwater Kent in the closet became the prime item of interest.

The Atwater Kent "Model 20", model number 4640, was the first of 4 versions of the 20. This one was first produced in 1924, and continued into the first couple of months of 1926. I'm not really sure about this one's original "birth date", but if the serial numbers were sequential, this one was probably produced in late 1925, as there were roughly 189,000 of these units produced, and ours is serial #154604.

The case has a hinged lid on the top, which give you access to all the connection points for the batteries, antenna, and speaker. It also has a small bracket on the back of the inside of the case for storage of the log sheets (visible in the photo above.)

As you can see in the photos, the inside of the case is in much cleaner condition than the outside, though I do intend to see if I can't clean it up to expose the original finish more clearly.

The interior of the radio is in fair condition, and complete, just in need of some cleanup. I have no reason to believe that this radio is not in good working condition. The tubes, which are all UV-201A diode tubes (except maybe one UV200A), all seem to be in fair condition, though my Sencore Tube Tester has no provision for this type of tube (which has only four connectors on the bottom, arranged in a square shape!) All the tubes are RCA "Radiotron" tubes, except one, which is a "Cunningham" brand, I assume it to be a replacement.

According to this detailed schematic, the radio requires 5, 22.5 and 90 volts DC! I sat and pondered forever how I would come up with these sorts of voltages, and I finally, after doing some research, I discovered how the old "Farm Radios" of the 1920s thru 1940s worked. There was usually an "A" battery used to power the tube filaments (between 1.5 and 5 volts DC), and either 22.5, 45, or 90 volts DC provided from a "B" battery for plate voltages. Some required a "C" battery that provided ~22 volts. I believe that "C" batteries weren't in use when the Atwater Kent 20 was produced, as it requires 2 "B" batteries, and one "A" battery. (I read on one collector's site that the "A" battery was often a 6-volt car or truck battery from that era, and was often borrowed from the car when the family wished to listen to the radio!)

The AK20 4640 requires +90v (or two 45 volt "B" batteries in series), and +6 volts (~5 volts, actually). Again, see the schematic for details.

So, obviously, we need some sort of power supply. BUT, first and foremost, we needed a speaker. So, I purchased an Atwater Kent model E2 wooden speaker on eBay. I noticed one of these with an Atwater Kent 35 receiver that is on display at, of all places, our very own Lawrence Co., Indiana history museum on the north side of the square in Bedford! The 35 is a very similar radio, with the exception that there is one more tube for the audio amplification circuit, and the three tuning units are ganged together in one knob instead of three (the AK radios of this era were TRF (Tuned Radio Frequency) receivers, unlike the Superhetrodyne receivers that followed in the early 30s, which basically used the same circuit theory we have today. More info on this is available here, about half-way down the page on the left.)

The E2 speaker, which hasn't arrived yet as of this writing, is a hair newer than the radio, which probably used a model N or L "Horn" speaker. I couldn't rope an affordable horn speaker on eBay, but I got this one for about $35 with shipping included, whereas the horns were going for over $100 total. It may need some restoration, too, but it doesn't appear to be too bad. Auction photo is below.

I have been studying some web sites and plans for building a power supply for the AK, as well as sending e-coorespondence back and forth with a couple of other antique tube radio enthusiasts, including Phil of Phil's Antique Radios at www.antiqueradio.org, a really cool site. He directed me to this power supply kit at Antique Electronic supply. So, at this point, (3/28/06), this is going to be our next move. More on that later!