I picked up this cute little non-working radio for twenty bucks. I am looking forward to getting it working again. I'm not really a fan of the mid-century modern look, so if I screw this up, I won't feel bad about it. These things are also still pretty common, so that's another reason to feel comfortable taking it apart, without worrying too much about messing it up. Also it's a pretty simple radio.
Controls (looking at the above photo): The knob on the left is the tuning knob - which doesn't work, because the cord that rotates the tuner is broken. A second cord attached to the tuner rotates the dial pointer. If I can get some cord and connect the knob to the tuner, then the dial pointer should also work.
The little white dome-shaped knob at the very center is a tone control. It would not turn at all, but I was able to dribble a little penetrating oil on the shaft, and now it rotates smoothly.
The knob on the right is the on/off/volume knob, and it seems to be working OK.
The radio does not work at all, and none of the tubes light up. I took the chassis out of the cabinet.
It's pretty clean. As you can see, there is no tuning cord going from the left knob to the tuner pulley above it.
Below, I cut the wires that connect the back panel antenna, so that the back panel wouldn't be flopping around while I attempt to repair the radio. This model has an auxiliary RCA type phonograph jack, and a switch to change the input from AM radio to Phonograph.
Back in the day, electrical plugs were not polarized. Depending on what way you happened to plug your radio into the outlet, the chassis might be at zero volts (grounded), or at 120 volts! For this reason, radio chassis were completely electrically insulated from the user. Later on, safety interlocks were introduced, so that when the back was removed, the 120 volt power plug was pulled from the chassis. Obviously troubleshooting a radio with a (potentially) hot chassis can be hazardous. Don't attempt this unless you know what you are doing!
Underneath. I've spotted half a dozen wax paper-and-foil capacitors. They are the yellow-brown cylinders, and they will have to be replaced. Another black "bumblebee" paper and foil capacitor is at the bottom right, and it will also have to go. If they haven't already failed, they will.
This radio is a typical "AA5", or All-American Five style, that uses the absolute minimum of five vacuum tubes to create a standard superheterodyne AM radio.
The AA5 design strings the heating elements of all five vacuum tubes in series. And just like an old strand of series Christmas tree lights, if one vacuum tube heater goes out, all of the tubes stop glowing.
Check out the red-circled part of the schematic: If any vacuum tube heater fails, there is no path for the current to flow.
Also I found a couple of tubes out of position according to the diagram at the bottom left, and one of them is not the correct type. I'm hoping that after I replace the capacitors and get a couple of replacement tubes, this radio might work OK. If it does, I will re-string the tuning knob and have a cool new toy for my knick-knack shelf. If not, well I've got a slightly less cool item for my knick-knack shelf.
The first update is Here:
The second update is Here:
The final update is Here:
2 comments:
I am so glad you set up this post I just found one of these today at a yard sale. I will be watching your post to see how it goes I have not plugged this one in yet but all the knobs seem to turn just fine.
Thanks for leaving a comment! Yes, the radio came back to life, and pulls in channels. I still need to follow the alignment procedure to make it a bit more selective, but it's going strong. Thanks for following along!
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