08-24-2021, 12:55 PM
Later last night I continued to work on the 48-482. I replaced both the dial bulbs, which was something of a job. Both bulbs were quite stuck in their sockets, and the socket assemblies were very difficult to remove from the back of the dial plate, things are quite cramped back there, especially on the tuning condenser side. I ended up having to loosen the dial plate, and then put it back, but eventually got both bulbs replaced, and the sockets lubricated with a little of my gun oil mixture. (50% 10X30 motor oil, 50% Marvel Mystery Oil) I also lubricated the shaft bearings of the tuning condenser and dusted off the plates of it with a little brush. It now tunes smoothly all up and down the range. Finally I replaced all the tubes. NOTE WELL ! There is an error in the paperwork which is not well noted, Where the paperwork says a 6SQ7 goes is actually a 7B6 ! This threw me the first time I restored one of these radios, but I remembered it this time.
Well, that was it. Time for the first test. I plugged the set in, and it came to life. No smoke. No loud noises. Both good signs. The dial bulbs came on fine. soon a hum came from the speaker. All good signs. I pushed in the Broadcast Band button, and began to tune up and down the band with my test antenna connected to one of the antenna terminals. I could hear faint stations in several places on the dial. I tried Shortwave, and heard nothing but slight variations in the background hum and hiss. Then I tried FM, and got nothing but the background hum.
I turned the radio off, and unplugged it again, and sprayed the whole push button assembly well with contact cleaner. I went up and down the row of buttons pushing each one in turn about a dozen times or more. I then let it dry out for an hour or so, and tried it again. BCB was far less noisy, and more stations came through, still without what I know is normal volume. Shortwave was still quite dead, although there was more noticeable variation in sound as you tuned up and down the dial. FM came to life. There were quite a few stations which came through clearly, and at what sounds like normal volume. No distortion, just sounds FINE. FM is working as it should, which will save me a LOAD of headache.
So, that's where it stands now. Next I will begin to chase back through the circuit and see why the BCB and shortwave are not up to snuff. That should be pretty straightforward. The fact that the FM works fine pleases me. It also means I don't have any problems with the audio amplifier circuits. I suspect the problem lies in the IF for the AM / SW which is 455 KC, and is separate from the 910KC used fore the FM.. Although they appear to use the same IF transformers, they are tuned separately on those transformers. We shall see.
Well, that was it. Time for the first test. I plugged the set in, and it came to life. No smoke. No loud noises. Both good signs. The dial bulbs came on fine. soon a hum came from the speaker. All good signs. I pushed in the Broadcast Band button, and began to tune up and down the band with my test antenna connected to one of the antenna terminals. I could hear faint stations in several places on the dial. I tried Shortwave, and heard nothing but slight variations in the background hum and hiss. Then I tried FM, and got nothing but the background hum.
I turned the radio off, and unplugged it again, and sprayed the whole push button assembly well with contact cleaner. I went up and down the row of buttons pushing each one in turn about a dozen times or more. I then let it dry out for an hour or so, and tried it again. BCB was far less noisy, and more stations came through, still without what I know is normal volume. Shortwave was still quite dead, although there was more noticeable variation in sound as you tuned up and down the dial. FM came to life. There were quite a few stations which came through clearly, and at what sounds like normal volume. No distortion, just sounds FINE. FM is working as it should, which will save me a LOAD of headache.
So, that's where it stands now. Next I will begin to chase back through the circuit and see why the BCB and shortwave are not up to snuff. That should be pretty straightforward. The fact that the FM works fine pleases me. It also means I don't have any problems with the audio amplifier circuits. I suspect the problem lies in the IF for the AM / SW which is 455 KC, and is separate from the 910KC used fore the FM.. Although they appear to use the same IF transformers, they are tuned separately on those transformers. We shall see.
