11-22-2014, 04:16 PM
I pulled the chassis out of my 40-150 because the dial cord had slipped, and while I was realigning it I discovered the short wave band doesn't work. I vaguely remember when I first worked on it in 2007 I could never get the SW band working. It was one of the first radios I'd worked on. I put it back together, thinking I'll never listen to short wave on this, anyway.
This time, I know more about radios, but I still can't get the short wave working. Since the BC and Police bands work fine, I suspected the band switch. I buzzed out all the band switch connections and it looks like it's wired correctly and everything makes good contact.
I checked the wiring of the coil, and that seems to be wired fine. I have continuity everywhere on the coil. Since it is just one coil with 4 taps, I don't think the radio would work at all if there were any opens in the coil.
I injected modulated RF into the converter tube with frequencies in the middle of each band. I get a tone with each of the two lower bands, but not shortwave. I also used a coil of wire near the loop antenna, connected to my signal generator. Same result.
The oscillator does not seem to be oscillating on short wave, based on the "two radio" test. The known good radio (a 42-350) squeals on the other two bands, but not short wave.
I changed the 7J7 converter tube for an NOS, thinking maybe it was having trouble oscillating at the higher frequencies. No luck
The 7J7 tube socket wafer is badly cracked on this radio. I'll have to replace it, but in the meantime I buzzed out the electrical connections between tube and socket, and I have good contact all around. Anyway, the other bands work.
I don't guarantee that all my tests and checks were done correctly, but I was pretty careful and repeated most of them more than once.
Scratchin' my head over this one. If anyone can offer any more suggestions for troubleshooting the SW band, I'd love to hear them.
This time, I know more about radios, but I still can't get the short wave working. Since the BC and Police bands work fine, I suspected the band switch. I buzzed out all the band switch connections and it looks like it's wired correctly and everything makes good contact.
I checked the wiring of the coil, and that seems to be wired fine. I have continuity everywhere on the coil. Since it is just one coil with 4 taps, I don't think the radio would work at all if there were any opens in the coil.
I injected modulated RF into the converter tube with frequencies in the middle of each band. I get a tone with each of the two lower bands, but not shortwave. I also used a coil of wire near the loop antenna, connected to my signal generator. Same result.
The oscillator does not seem to be oscillating on short wave, based on the "two radio" test. The known good radio (a 42-350) squeals on the other two bands, but not short wave.
I changed the 7J7 converter tube for an NOS, thinking maybe it was having trouble oscillating at the higher frequencies. No luck
The 7J7 tube socket wafer is badly cracked on this radio. I'll have to replace it, but in the meantime I buzzed out the electrical connections between tube and socket, and I have good contact all around. Anyway, the other bands work.
I don't guarantee that all my tests and checks were done correctly, but I was pretty careful and repeated most of them more than once.
Scratchin' my head over this one. If anyone can offer any more suggestions for troubleshooting the SW band, I'd love to hear them.
John Honeycutt
