Atwater Kent - Model 20 : Important Documents

One of the first things I do once I have acquired a new "treasure" is to gather together all the information I can find and stick it in one place.

To this end, here is what I have found online and scans of some of the paperwork I have acquired. Most will be specific to the Model 20 but some may also cover other Atwater Kent radios:

Sadly I do not have a high resolution scan of the Model 20 log card which I believe is Form F 103, can you help?

This is Form F 194 which would suit a single dial Atwater Kent radio.

The file is scanned at 600DPI and if printed at the same resolution it should be the same size as the original.

A small amount of cleanup may be required to print correctly on your printer.

Download the PNG file HERE (49MB)

At the right is the "Radio Log Cards and Important Instructions" envelope which was used to organize all the paperwork. This would typically be held in between the two clips inside the radio.

If you are wondering what those clips were used for, now you know!

The file is scanned at 600DPI and if printed at the same resolution it should be the same size as the original.

A small amount of cleanup may be required to print correctly on your printer.

Download the PNG file HERE (57MB)

This is the back of the envelope so you can see the fold patterns and get an idea of how it was put together.

I plan to clean up these images and generate a pattern which can be printed out via a large format printer at a FedEx office or similar.

The pieces I have are too fragile to use and would crumble if handled more than a few times.

The file is scanned at 600DPI and if printed at the same resolution it should be the same size as the original.

Download the PNG file HERE (56MB)

I have several of the loud speaker instruction sheets and they seem to be generic enough to suit any of the horn type loud speakers. As far as I know they all have a similar adjustment underneath and all users should heed the warning about connecting them to the receiver with the correct polarity.

As with all the images I have used full color images so you can see the original colors and then change it to black and while to increase contrast for printing.

The file is scanned at 600DPI and if printed at the same resolution it should be the same size as the original.

Download the PNG file HERE (54MB)

This is the Atwater Kent Radio Service Manual from 1928.

This manual covers from the Model 10 to the Model 52 including accessories such as the power units and loud speakers.

This manual was a pain to find so hopefully this will help some people out and ease frustration.

Download the PDF file HERE (8MB)





This is the Atwater Kent Radio Instruction Book Vol. 2 from 1925.

The instruction book covers the Model 10 through to the Model 24 and contains important photographs showing battery cables, battery boxes and other accessories.

Download the PDF HERE (14MB)








I'm looking for high resolution scans of the following two forms: F91A and F101 as shown in the picture below. If you have scans or can point me in the right direction I would appreciate it!

Atwater Kent Model 20 "Big Box" - 1924

Ok, you got me. This isn't technically an amateur radio blog post but I would argue that radio in the early 1920's was the pursuit of the amateur, the enthusiast and the tinkerer. The amount of crossover between commercial broadcast radio and amateur radio in those days was much greater than it is now. Anyway, that's my excuse ... but why the Atwater Kent Model 20?

The model 20 or AK20

Well, to make along story short, I found an example of this Atwater Kent model sitting in a flea market stall in Hot Spings Arkansas. It looked like it had seen better days but was fully complete including the five '01A' vacuum tubes. The owner wanted $200 for the radio and explained the better part was the included horn type loud speaker which was worth $150. The horn speaker looked to be in fairly bad shape and lacking any way to test it I cheekily asked if he would take $50 for the radio ... "Sure", he said and my wallet was instantly $50 lighter.

Now I have a few vintage radios at home, perhaps a few too many depending on who you ask, and I consider them all to be interesting examples in their own right. More or less money, time and research was employed to create these radios and a great variety of circuits and designs was the result.

First impressions told me this was different, I had never owned anything like the Atwater Kent radio before. It was certainly older than my other radios but it was also constructed unlike any other radio I owned. Even under layers of grime, dust and mud dauber's nests this was obviously an article of quality. The finish on the wood cabinet and the metal front panel had seen some heat and were very badly checked in addition to the 90 or so years that had taken its toll. On the lip of the hinged top was a protected area which still showed how the finish looked originally, the dark mahogany and subtle gloss hinting that it had once looked very smart indeed.

The model 20 compact or AK20C

Once I had Internet access again I started to research the model 20 and try and learn something about it. It was at this stage, after some initial confusion, that I noticed that my model 20 was the older and perhaps slightly rarer "Big Box" version. There isn't much between them but some important differences crop up as far as restoration goes, for example:

Most references I found online suggested that the front panel of the model 20 was painted with a crinkle finish however this was only true of the later versions.

In an Atwater Kent advertising booklet, published at the time, they write, "The front of the cabinet is of metal with a deep brown mat surface which brings out the sparkling sheen of the lighter brown Bakelite dials, knobs, etc., and the nickel-plated trimmings."

I'll need to clean my Bakelite parts and possibly wax them to bring up the original "sparkling sheen" of the tuning, aerial tap and filament rheostat knobs.

A suggestion from the Antique Radio Forums that Rust-Oleum Earth Brown paint followed by black KIWI boot polish applied using 0000 steel wool sounds like it would come pretty close to producing the right finish and will probably be the path I choose when I refinish the front panel.

This AK20, from The Backwood Realm, appears
to have the original finish and looks similar to mine.

For the woodwork we're fortunate to find the description below and some more research indicates that nitro-cellulose lacquer was used at the time and is still available now.

"The cabinet of the Model 20 Receiver, pictured above, is of solid mahogany, stained a dark brown, then shellacked, triply lacquered, and rubbed to a dull, glossy, long-wearing finish."

Overall it seems very understated compared to modern electronics, even down to "The name plate, of dull bronze, is both distinctive and unobtrusive."

I hardly need to say, to most folks at least, that Ebay is a wonderful, and terrible, place to shop for antique radio parts. Wonderful because at any one time there are parts available for just about any radio you might have and terrible because you'll be jostling with tens, or hundred, or thousands of other collectors and re-sellers ... many of which have some very deep pockets indeed!

Unused Atwater Kent Radio Log card.

After vowing I would never pay Ebay prices I lasted approximately 3 minutes and then started looking on Ebay for some of the things I knew I was missing.

Before too long I had found an all-important unused "Atwater Kent Radio Log" card and envelope. I intend to scan these items in with a high resolution flat bed scanner and make copies to use and share.

Also I was able to get a set of three tuning knobs since one of the originals on my radio was shattered. Although someone had thoughtfully placed the remains inside the cabinet it was never going to piece back together well enough to look "right"

I had found the Atwater Kent Radio Instruction Book Vol. 2 online and printed out a copy but couldn't resist the temptation to pick up an original as well as another envelope along with some instruction sheets for various models of AK loud speakers.

I already own a modern ARBE-III battery eliminator so this really left only one thing to find ... a loud speaker.

Even the parts you don't see, are expensive.

I should have known that finding "the right loud speaker" for the model 20 would not be a simple task. While it will work with many different speakers including later cone style Atwater Kent units and those manufactured by other companies, the "right" speaker ... the type shown in all the period advertising literature ... is the Atwater Kent type M, L, H or R radio speaker.

All but one of those models allegedly used pot metal in their construction which eventually succumbs to the dreaded "pot metal disease" making it crack and expand. I have dealt with pot metal disease before and have no intention of doing battle with it again ... this left one model, the model M, as the one I was looking for.

Ok, so there was one model M listed on Ebay and it looked to be in good condition as well as "working" according to the seller. In fact the more I looked at it, the better it looked ... it seemed to be in very nearly new condition. After I finished drooling over the photographs I decided that I would limit myself to $100 not including the $50 shipping involved. The shipping was more than average and I hoped this would keep bids low and reduce the amount of interest. This seemed to work for a while ... the bids topped out at around $80 and I thought I might be on a winner, however this was short lived and the bids jumped to over $100 and kept on going. "Ah well", I thought, "such is life". I knew there would be an vintage and antique radio auction coming up in a month and I could probably find something there at a reasonable price.

The Atwater Kent Type M Loud Speaker.

At this point I took a shower, which is something I would recommend to anyone suffering some disappointment ... or a bath. Worst case you end up cleaner if still disappointed which is surely a small improvement.

At the same time my wife, who perpetually despairs of ever buying the right gift for a husband who is notoriously difficult to buy for, noticed my dejection and moved over to my computer which I had foolishly left logged into Ebay (I should know better, really).

A furious round of bidding started between my wife and a number of others who knew little of her determination to win this auction. I won't mention the final amount, I would like to say because, "One doesn't discuss money" but mainly because it still makes me a little woozy to think about.

If you were bidding on that same speaker then I apologize, but you never really stood a chance.

After further research I've learnt a bit more about the internals of the AK20 and uncovered the meaning behind its three tuning dials and various other controls. In order to provide more amplification, not to mention more selectivity, the AK20 uses three largely identical tuned circuits. Each tuned circuit is controlled by a separate knob on the front panel and all three must be "in agreement" before you will hear anything from the loudspeaker. Next comes the detector circuit which converts the amplitude modulated radio frequencies into audio frequencies and finally two further stages of audio amplification.

The other controls on the front panel are the aerial tuning switch which selects different taps on the first set of coils and the filament rheostats. The filament rheostats, in addition to correcting the voltage supplied by the batteries to the vacuum tube filaments, also act as the volume control by lowering the filament voltage which in turn lowers the volume from its maximum to a comfortable listening level.

Next steps will involve re-finishing the front panel and cabinet, checking tubes along with the few capacitors and resistors, then a careful power-up with high impedance headphones ... the AK loud speaker can wait until I am absolutely sure that it is working as intended!

I hope to update the blog as I progress, as well as uploading pictures and more detailed data such as circuit diagrams and service information HERE.

Shock and Awe - The story of electricity.

Amateur radio has a long history, going all the way back to wireless experiments in the late 1800s. However the study of electricity has its roots in the observation of natural phenomena and stretches back much further.

I ran across this excellent three part documentary detailing the story of the discovery of electricity. The presenter is Jim Al-Khalili, currently Professor of Theoretical Physics and Chair in the Public Engagement in Science at the University of Surrey. He not only knows his stuff, he is also an interesting and engaging speaker.

The documentary runs for three hours but is worth your time if you are interested in the story of electricity and the people behind its discovery and history. I hope you find it as enjoyable as I did.

What has been happening?

Anyone looking at my blog could be forgiven for thinking that I had dropped off the face of the earth for a while, has nothing been happening in my world?

Well, the answer is that a LOT has been happening and all at once. My daytime job has become busier and there have been several non-radio projects at home that needed to be completed. All this has kept me away from Amateur Radio blogging even though I have spent more time on the computer than usual.

In between projects I did manage to stumble across this video of Rear Admiral Grace Hopper explaining just how "long" a nano-second is and what it looks like. This has relevance to radio as we're usually well aware of frequency and wavelength but don't usually spend too long thinking about speed.

From Wikipedia : Rear Admiral Grace Murray Hopper (December 9, 1906 – January 1, 1992) was an American computer scientist and United States Navy officer. A pioneer in the field, she was one of the first programmers of the Harvard Mark I computer, and developed the first compiler for a computer programming language. She conceptualized the idea of machine-independent programming languages, which led to the development of COBOL, one of the first modern programming languages. She is credited with popularizing the term "debugging" for fixing computer glitches (motivated by an actual moth removed from the computer). Because of the breadth of her accomplishments and her naval rank, she is sometimes referred to as "Amazing Grace." The U.S. Navy destroyer USS Hopper (DDG-70) was named for her, as was the Cray XE6 "Hopper" supercomputer at NERSC.

What is the AM-6155/GRT-21 ?

FAA AM-6154/GRT-21 Amplifier

From the website of N1RWY

The FAA used the AM-6154 and 6155 amplifiers in the early 1980's as ground-to-air AM transmitters. The 6154 was designed to cover 118-136 MHz and the 6155 to cover 225-400 MHz. Both models were set to 50 watts output, and amplified an AM exciter.

Both models were rack-mount, 7" high, 19" wide, and about 24" deep; they weigh about 75 pounds and have an internal AC power supply that can be used on 120/240 VAC. They are built so they have a slip-in RF drawer that contains the RF amplifier itself. The main chassis holds the power supplies and a small blower. No T/R switching is included. Because they are intended to be used with the exciter, the amplifier circuitry expects to get some DC control signals from the exciter which have to be simulated by some modifications.

The reason the amplifiers are so interesting to V/UHFers is because they are capable of outputting over 400 watts on 2, 222 or 432 MHz with only a few hours work and almost no extra parts. This is because they use the 8930 tube (or the Amperex equivalent, the DX-393), which is basically a 4CX250R with a 350-watt anode. 50 watts average power of AM is actually four times that power peak; or 200 watts; and these things were designed to do that all day, every day. That's why they used such a high-power tube for only 50 watts output power.

The RF drawer of either model can be modified for ANY of 2, 222 or 432; but as it comes from the factory, modifications HAVE to be made for any of the three bands. In general, the mods involve redesigning the RF grid circuit to be more efficient and to tune one of the ham bands. The plate circuit in either model can be used on any of the three bands, although use at 400 watts on 432 MHz places a big strain on the stock plate DC choke and plate blocking capacitor, which almost always have to be reworked for serious 432 MHz use. They have apparently proven able to withstand high power on 144 and 222 MHz without modification, although the mods do not hurt.

The power supply chassis is composed of three smaller drop-in chassis, an additional metering PC board, and a 400 Hz 120VAC blower which is powered by a DC-to-AC converter (one of the three drop-in chassis). The high-voltage power supply uses a very compact and lightweight transformer, a dual-section oil-filled filter capacitor, two screen voltage dropping resistors and a string of three zener diodes to regulate the screen voltage. Another drop-in chassis houses the filament transformer which also provides grid bias power and another winding to provide power to the DC-to-AC converter which drives the very small, compact 400 Hz blower (which is able to cool the large tube due to the high speed, 5500 RPM, of the blower).

A front-panel-mounted meter with 12-position switch is also wired to a PC board which contains circuitry that originally monitored the output power and antenna VSWR in addition to the blower current, filament voltage, grid, screen and plate voltage, and plate current. The RF drawer contains a directional coupler and low-pass filter which are almost always removed from the output of the amplifier (and sometimes rewired to the input side) because they don't handle 400+ watts very well.

So, where can you get one?    

Most of the amps are sold by Fair Radio in Lima Ohio. They advertise in QST. Sometimes they can be found at hamfests and there have been reports that a few have been picked up from government surplus sales. Fair Radio asks $235 for the AM-6154 and $285 for the 6155. (Based on early 1997 figures) Fair Radio has by far provided the lion's share of them, probably well over a couple thousand to US hams alone.

They are extremely popular among US V/UHFers and usually command a $300+ price tag, whether modified or not (because the shipping alone totals around $35 for UPS Ground!). Recent estimates by Harry Brown, W3IIT of the Packrats, are that there are OVER several hundred in the Philly area alone; and Ev Tupis, of the Rochester VHF Group, estimates ALMOST that many in northwestern NY state! They're great amps - not 8877's but the price is hard to beat.

[ Thanks to Steve, KO0U/1, and Harry, W3IIT, for the summary and history of these fine amplifiers. ]

Now I understand - Standing Wave Ratio (SWR)

There are great books out there that explain radio principals in a plain and straightforward manner. Many are vintage military manuals whose primary aim was to give a functional understanding of the theory involved without getting caught up in the interesting but ultimately unnecessary details.

Modern material on the other hand can sometimes miss the mark of providing a functional understanding in favor of trying to completely address the high level theory and leaving practical matters to be addressed later ... or perhaps never.

The AT&T training video certainly hits the mark when it comes to explaining and showing the properties of radio waves. It shows how they are affected by termination and changes in impedance, what resonance looks like, how terminated and non-terminated lines reflect waves and much more.

Material like this is well worth the time of anyone who has an interest in radio or electronics.

More video are available from the AT&T archives here : http://techchannel.att.com/showpage.cfm?ATT-Archives

Coil Winding using the Gingery Coil Winder

Anyone who has seen the video below from KC9KEP will probably be wondering where he got the coil winder used to make those high Q coils with universal windings.

The design itself is based on the Morris Register Company (MoReCo) Coilmaster and modified for home brewing by Dave Gingery. His excellent book is available from lindsaybks.com and provides plans that use parts and tools commonly available in the home workshop.

Gingery coil winder by KC9KEP

Another resource for coil winders is a page from K5BCQ that shows the original Coilmaster, a different home brew plan and a large volume of useful information.
A vintage text is also available which covers inductor (coil) design in significant detail and should be downloaded by anyone who REALLY wants to know what they are doing. It is available here.

iPads and e-Readers as book replacements?

I've recently started to acquire reference books as PDF files since getting an iPad. I was initially skeptical of this idea after being disappointed trying to read PDF files on a Sony e-ink device. After some software updates and a little experimenting I have found the iPad to be a completely different experience.

The large screen size and, more importantly, the quick navigation have made the iPad a logical choice for reading though a book, magazine or reference manual. Now that Apple has made some tweaks to the book reading application you are now able to sort PDF files into collections and this improves on the slightly clunky, although intuitive, bookshelf metaphor.

The cost is certainly an issue as iPads are not cheap and are rarely discounted. I will suggest that there are other factors which should be balanced against the initial cost:

1. Convenience: The iPad is always the same size and weight. No matter if it carrying one book or one-thousand it remains a convenient size that can be slipped in a backpack or carried in a case.
2. Speed: There are several features in software that allow you to quickly turn to the exact page you require or look-up a reference or keyword in the text. Even older books that have been scanned benefit from being able to see many pages at once or bookmark multiple pages for reference later.
3. Intuitive interface: The bookshelf metaphor used by the iPad's reading application is expanded by the idea of collections of books that the user can manage. Pages are turned by taps or swipes and a single tap in the center of the page brings up additional navigation options. Other iPad gestures like 'pinch to zoom' also allow you to zoom on details or expand a diagram to fill the whole screen.
4. Long term cost of ownership: Reference books, in particular educational text books, are often priced over $100 USD for a single volume. The same books are often available for much less in electronic format due to the elimination of printing, shipping and storage costs. For people such as myself the books I would like to own are often out of print or, if copies are still available, they are being sold at exorbitant prices. The iPad makes it possible for me to own and enjoy these books with the additional benefit of them not taking up shelf space.

An Apple iPad running the Books application.

There are other tablet devices available and I have used a few for brief periods of time while evaluating different applications. It is my impressions that the iPad does a better job of integration between applications and maintains a consistent user interface across all its applications. There are certainly more options for customization and experimentation on other platforms but for straightforward functionality Apple have the lead at the moment.

As a book collector I hope that we continue to see books printed and I will certainly keep collecting antique books but I do foresee a time when digital books will become the dominant media. I think we have only seen the tip of the iceberg when it comes to digital books, there is much more to come.

To read more about the impact of the Apple iPad in Schools read : Goodbye Textbooks, Hello iPad from PCWorld