Instructables

How to fix a classic American AM tabletop tube radio

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Step 13: Troubleshooting and enjoyment

My radio doesn't quite work right!

It hums! If you replaced the filter caps, there's a chance you have a weak rectifier tube or a bad audio amp tube.

It's deaf! Make sure your antenna is ok and wired properly. Try turning the radio. The antenna is directional. If that doesn't solve it you may have a weak tube.

It doesn't play very loud before it sounds fuzzy. You may have a weak audio amp tube. Peek inside the cabinet while the radio is on (remember not to touch any metal so you dont get shocked!) If you have a tube that has a deep violet or deep blue glow inside the glass while it's powered up it may be a worn audio amp tube. Note the position of the tube on the chassis, UNPLUG the radio, get the tube out and look up it's number on the web. If the tube comes up as being an audio amp tube it probably needs replacing . A common audio amp tube on AA5 radios is the 50L6 and the 35L6. They are cheap and easy to get from tube vendors.

I get a raspy buzzing noise between stations. Electric eye lamps (lamps that turn off during the day automatically) have been known to create nasty noise on AM. Check on a known good AM radio to see if you get the same noise. If you do, your culprit is not the radio itself.

Radio sounds good at first then begins to sound distorted as time passes. You may have an out of spec resistor. While the radio is on, peek inside the cabinet being careful not to touch any metal so you don't get shocked. Look for a tube who's metal structure inside is glowing orange or red like its gonna melt. I'm not referring to the heater filaments as those are supposed to glow orange. If the tube structure itself is glowing from heat you may have a bias problem which is more than likely in the audio amp circuit of the radio. Obviously you can't perform this visual check on all metal tubes. Either way, it's time to get out the schematic and meter.

Following these same instructions I have resuscitated several old tube radios. The AA5 was built for simplicity thus there isn't much to go wrong and they are forgiving. Once your radio is up and running, enjoy it. Use it every so often. Just like an antique car, its bad to have it sit unused. Fire it up every now and then and show off your work!

into old tech? follow me on instagram as vintagetechguy to see random pics of interesting old tech.

 
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MarkS44 months ago

I recently restored my first AA5 radio, a GE model 101 made in 1948. Many thanks to KE4MCL for writing up this Instructable. It was quite a help. I replaced all the paper and electrolytic caps. I also had to replace the dial cord. I was surprised that I did not have to adjust the alignment any at all to pick up even the weakest stations in my area. Prior to this I have done very little with tube electronics, mostly chips and transistors.

This project turned out so well, I will try to bring a '50's Pilot AF-605 AM/FM mono only Hi-Fi tuner back to life next. That Pilot tuner looks clean under the chassis but I think I might have to replace quite a few more parts than on the GE. I am just starting research on the Pilot trying to find a schematic or service manual. Would anyone know where I can download either one? Thanks in Advance.

kong25504 months ago

thank you

Wyle_E1 year ago
Memories... I'm of the last generation of techs who trained on tube equipment before we encountered transistors. At one time I had the standard AA5 schematics and all of the parts values and tube bases memorized. Repair shops used to have isolation transformers to make these radios less dangerous, but another solution was to measure the voltage between the chassis and an external ground. If the chassis was hot, reversing the power plug put the chassis on the neutral side of the line. Dial cord was just fishing line. Not monofilament, but nylon braid. Hardly anyone sells it as "dial cord" anymore, but fishermen still use it. Waxed dental floss will also work, but it's harder to tie. "Loctal" tubes have a glass envelope with a metal base that has a little bump on one side. Pushing on the bump, to move the tube sideways, releases the lock so you can pull the tube. This system was invented to keep tubes in aircraft electronics from vibrating loose, and it's pretty rare in AA5 sets.
I've got a tallboy radio with 9 tubes in it... would any of the instructions here be significantly different? Any chance of dangerous charge being stored in any of the capacitors?
ke4mcl (author)  gravityisweak1 year ago
It would be very similar. Still have all the same parts to replace. Your radio might have a power transformer in it thats all.

Leave it unplugged and switched on for a few hours and they will surely be discharged.
stienut3 years ago
Super ible. I can't wait to see what's up with my 1936 American Bosch. Very well done, indeed!
jernlee4 years ago
Thank you very much for taking the time to help the people that do not know Thanks again jerry
desertdog5 years ago
Excellent and informative. I can now feel more confident about purchasing a used radio knowing that it may be repaired. I also liked the "natural selection" comment. Whatever happened to personal responsibility.
w8znx5 years ago
well done dit dit
Just found this site! Very well done. I can't wait to tear down my old radio and see what happens.
canerods6 years ago
You covered the process very well. Easy to read and understand. Thanks very much! You may want to add this tip in future: Since speaker cones are very fragile. One way to keep from damaging the paper cone while your working on the radio is to cut a thin cardboard shield and tape it to front of the speaker to protect it. Be sure your tape only contacts the metal frame and your cardboard shield -- not the speaker cone material itself.