Post by Admin on Oct 21, 2019 21:52:40 GMT
A separate category for Olde Radios, nice idea. Until then here's another of my old collection, a 1945 Hallicrafters Model S-20R "Sky Champion".
This was acquired from an acquaintance several years ago, not working. First problem, the speaker cone was crumbling. This speaker was an electro-dynamic type. This type didn't have a permanent magnet as the technology of the times didn't have strong magnets. Instead an electromagnet was used. It doubled as a choke coil for the power supply. The easiest way to replace the speaker was to separate the electromagnet (field coil) from the speaker and keep it as the power supply choke coil. Then a newer speaker was mounted and connected to the output transformer. You can see this in the picture.
Next, the power supply transformer developed a short in half of the B+ winding. Intermittent at first, then permanent. I had an old transformer I'd been pushing around for many years. It was from some military gear that was cannibalized. It had all of the necessary voltages and was a perfect fit.
A few leaky capacitors replaced and a minor tune-up has it working.
It still has a problem with one of the RF coils for frequency band 4. This coil is in the B+ circuit of the RF amplifier stage and has an intermittent short. I actually saw it arcing once. The coil wire is like frog hair so trying to repair it would destroy it. I'll put up with it until I can find a suitable replacement.
All in all, it's a good performer, fairly sensitive. It has a beat frequency oscillator (BFO) so it will receive CW and SSB. It covers 550 kHz to 45 mHz in 4 bands. It has selectable AVC, noise limiter, 3 step tone control and RF gain control.
This was acquired from an acquaintance several years ago, not working. First problem, the speaker cone was crumbling. This speaker was an electro-dynamic type. This type didn't have a permanent magnet as the technology of the times didn't have strong magnets. Instead an electromagnet was used. It doubled as a choke coil for the power supply. The easiest way to replace the speaker was to separate the electromagnet (field coil) from the speaker and keep it as the power supply choke coil. Then a newer speaker was mounted and connected to the output transformer. You can see this in the picture.
Next, the power supply transformer developed a short in half of the B+ winding. Intermittent at first, then permanent. I had an old transformer I'd been pushing around for many years. It was from some military gear that was cannibalized. It had all of the necessary voltages and was a perfect fit.
A few leaky capacitors replaced and a minor tune-up has it working.
It still has a problem with one of the RF coils for frequency band 4. This coil is in the B+ circuit of the RF amplifier stage and has an intermittent short. I actually saw it arcing once. The coil wire is like frog hair so trying to repair it would destroy it. I'll put up with it until I can find a suitable replacement.
All in all, it's a good performer, fairly sensitive. It has a beat frequency oscillator (BFO) so it will receive CW and SSB. It covers 550 kHz to 45 mHz in 4 bands. It has selectable AVC, noise limiter, 3 step tone control and RF gain control.
