If you haven’t heard of an “all-American five,” then you probably don’t dig through bins for old radios. The AA5 is a common design for old AM radios that use five tubes: a rectifier, an oscillator/mixer, an IF amplifier, a detector, and a single tube for driving the speaker. [Mikrowave1] took an old specimen of such a radio from the mid-1950s and wanted to restore it. You can see how it went in the video below.
One feature of the design is that the set had a “hot chassis,” which means you really want to use an isolation transformer before you work on it. We were taught to touch a chassis with the back of our hand first because of radios like this. If it is “hot,” the muscle contraction would throw your arm away from the radio instead of forcing you to grip it uncontrollably.
The GE radio had many quality design touches you don’t always see in a radio like this. The mix of brands indicates that the radio has had tubes replaced in the past. It also had a clearly replaced electrolytic capacitor. Surprisingly, all the tubes were good, although the power output tube was marginal. However, a light bulb was bad and required a little surgery to allow for a slightly different replacement.
Some capacitors were neatly replaced, also. A lot of cleaning and testing later — along with a dropped tool — the radio was ready to play again. Fixing radios from this era is a great hobby. You can get to everything and you don’t really need anything fancy, although a tube tester is helpful. The classic method of troubleshooting is to either find audio on the volume control or not and then work your way backward or forward using a signal tracer or — since they are so readily available now — a scope. Alternatively, you could inject a signal at the volume control and work your way through the circuit until you can or can’t hear the injected signal.
Not the first tube radio we’ve watched being restored, of course. Need a tube tester?
The best AA5 mod I saw was in QST for June 1971. Someone converts it to shortwave. They add a solid state converter. A BFO. They add some feedback in the IF for better selectivity. They added an isolation transformer. There was even an optional magic eye tube.
I couldn’t afford it at age 11
I was just a few years younger, at the end of the tube-era. You woumd think that they would be everywhere, but at 14 nop one would give me one becase they were afraid I’d get myself electrocuted. I did eventually get a heahkit GR-64 with paper route money ($20) and a few years later a used Realistic DX-150
Now I have a box of them and no time!
Hamfests used to have hacking contests, where participants were given some old piece of gear and challenged to make something “new and improved” out of it. AA5 radios were a common starting point because they were so common. Participants built all sorts of things; RF signal generators, resistor/capacitor testers, shortware receivers, etc. One of the more impressive ones was an 80M AM transceiver built out of an AA5.
A Hallicrafters S-38 is just an AA5 for shortwave.
In the early sixties Popular Electronics had an issue with a few AA5 conversions. One was a theremin.
I was fortunate enough to buy a 1941 Westinghouse W785 medium wave/shortwave seven tube receiver from a farmer’s garage (barn?) sale back about 30 years ago. I refinished the beautiful wood case and all I had to add to make it work like new was a new 6U5 magic eye tube! I wasn’t smart enough then to replace all the electrolytics before I turned it on but everything worked fine!
It still works great. It’s one of those shortwave receivers with countries and cities marked on the display. It has five bands, 19m, 25m, 31m, a band covering 5.9 Mhz to 19 Mhz and the medium wave band. It has juke box like buttons like old car radios had to pre-program stations. It also has an aux phone input for a ceramic cartridge record player. I know that it receives the AM band fine, but never have had the chance to hook it up to a long antenna to check the other bands. Probably needs realignment. Fortunately I found the schematic and alignment info online.
Doesn’t sound like an AA5
Of course it’s not. Just wanted to describe an earlier type of radio.
Forgot to mention that it has a humongous heavy power transformer so it is not “off the line” and also the speaker doesn’t have a permanent magnet but a speaker field coil.
Interestingly enough, the speaker field coil often did double duty as a filter choke in the power supply.
Some of the biggest problems restoring old radios involve the case, not the electronics. Knobs used to be an issue and 3D printing has helped that, but the old wooden cases had a very thin veneer that often had peeled up in places. Or it was badly scratched or water damaged and you couldn’t sand it out because of the thin veneer. I have three or four old radios that I hope to restore some day, but I’ll probably end up trying to make new cases for them from scratch.
“If you haven’t heard of an “all-American five,” then you probably don’t dig through bins for old radios”
Or you don’t live in America.
Skill issue
Seems like a simple design, seems like a no brainer for other countries to copy it.
This can be a deep rabbit hole. This is an article for Hack a Day.
The Hazeltine Corporation patents.
I thought exactly the same.
Unfortunately my first freebee was an all american 4. They weren’t uncommon. They’d leave out the IF stage, a single can with two slug coils only it worked for widely spaced locals only. For me it was useless. 2 crap locals 30kHz apart and the stronger good Chicago station 30k from our local pre NPR wideband station. Talk about when Gimbal hits the cymbal! It’d crash into my top 40 hits on WLS.
I went 2 steps further down hacker lane then to a car radio and ran it off of a model train transformer with diodes and a cap. That form as a line operated radio was the 6 tube design with a RF stage, of which there were some. I had one a few years later.
Correction for the copy. The audio was normally done with 2 tubes, the preamp tube had 2 detector diodes in it as well. Look at the picture.
Philips in the Netherlands made a kitchen radio series in the fourties/fifties with a 4 tube setup: uch21, uch21, ubl21,uy1n in the bx208u and later with the fourties series of tubes: uch41,uaf42,ul4,uy41 in the bx180u.
The capacitors in those series are covered with tar and are always broken. Positive thing was that when a capacitor got hot, it would melt the tar, making a visual inspection easy. Early 1960’s radios from philips use mustard colored capacitors and in all my years of repairing in only once came up on a broken one. I still leave them in when encountered.
The filaments in a “AA5”, in series, added up to 120v, as opposed to previous designs with 6v heaters (in parallel). When one went down the set was ‘dead’.
Cheap.