31-01-2023, 12:43 PM
With the demise of AM broadcasting seemingly accelerating,I've reluctantly decided that any future radio restoration projects must include VHF/FM reception. Thus resolved, I spaffed way too much dosh (given the nature of the radio) on a specimen from well-known auction website. The specimen in question is a Bradford Grand Award model 51912. Bradford was the brand name used by the W T Grant chain of US department stores. They went out of business in 1976, so that puts an upper limit on the manufacturing date.
It's a pocket AM/FM receiver. AM is MW only. FM is 87.5 to 108 MHz. It was described by the seller as having a few crackles from the speaker when switched on, but nothing more. It's curious that a US department store radio wound up in the UK. I'll post some pics next time, but some images are available on radiomuseum.org
It arrived well packed. Cosmetically, it's not bad. A little chip out of one corner of the case and a bit grubby. It was made in Taiwan, no surprises there. It actually feels quite well made, The case is reasonably rugged and the whole thing has a solid feel to it. Close examination reveals some drop damage - a PCB support pillar is broken and there's a crack in the PP3 battery holder. Easy to fix though. The battery clip has seen better days and will probably be replaced.
There appear to be nine transistors -- four easily recognisable ones plus five of a type I don't recognise. They are mounted flush to the PCB, have what appears to be a white ceramic lid and are marked either 920 Q18 or 920 R22. I haven't found anything out about these yet. I imagine they are high frequency types with short connection legs to avoid lead dressing issues. There's no schematic available, so that adds to the fun.
It's my policy to do as much troubleshooting as I can before starting any component replacement, at least on transistor sets, so on with 9V from the bench supply. Just crackled on both AM and FM. Band switch seemed flaky so time for the Deoxit. Now FM sprang into life. If seems quite sensitive although the audio is a little distorted. Incidentally, I really like the thought that''s gone into the telescopic aerial arrangement. The aerial, which is undamaged, is mounted on the removable back of the set. There's a little spring plate on the inside of the back which connect the aerial to the receiver by contacting a pin on the PCB when the back is replaced. No fiddly wires to get broken...
Still nothing on AM, though, apart from increasing amount of hiss as we tune up towards 1.6 MHz. A play around with my function generator (non-contact via a coil loop) reveals that AM IF is at 455kHz, but rather dead. Even more deaf when I tuned the function generator to 525 kHz to 1.6 MHz. AM RF alignment appears to be spot-on. Curiously, with the function generator set to 1.6 MHz, I can receive the signal on the radio at three places on the dial. I assume that, because I had to turn the generator output up ridiculously high to obtain a hearable result, I'm overloading the mixer and getting third order mixing products.
So that's as far as I've got: FM seems to be working fine. AM oscillator is working, but something's not right along the IF. I hope someone might find this interesting, and I'd love to know anything about those RF transistors if anyone's seen them before.
It's a pocket AM/FM receiver. AM is MW only. FM is 87.5 to 108 MHz. It was described by the seller as having a few crackles from the speaker when switched on, but nothing more. It's curious that a US department store radio wound up in the UK. I'll post some pics next time, but some images are available on radiomuseum.org
It arrived well packed. Cosmetically, it's not bad. A little chip out of one corner of the case and a bit grubby. It was made in Taiwan, no surprises there. It actually feels quite well made, The case is reasonably rugged and the whole thing has a solid feel to it. Close examination reveals some drop damage - a PCB support pillar is broken and there's a crack in the PP3 battery holder. Easy to fix though. The battery clip has seen better days and will probably be replaced.
There appear to be nine transistors -- four easily recognisable ones plus five of a type I don't recognise. They are mounted flush to the PCB, have what appears to be a white ceramic lid and are marked either 920 Q18 or 920 R22. I haven't found anything out about these yet. I imagine they are high frequency types with short connection legs to avoid lead dressing issues. There's no schematic available, so that adds to the fun.
It's my policy to do as much troubleshooting as I can before starting any component replacement, at least on transistor sets, so on with 9V from the bench supply. Just crackled on both AM and FM. Band switch seemed flaky so time for the Deoxit. Now FM sprang into life. If seems quite sensitive although the audio is a little distorted. Incidentally, I really like the thought that''s gone into the telescopic aerial arrangement. The aerial, which is undamaged, is mounted on the removable back of the set. There's a little spring plate on the inside of the back which connect the aerial to the receiver by contacting a pin on the PCB when the back is replaced. No fiddly wires to get broken...
Still nothing on AM, though, apart from increasing amount of hiss as we tune up towards 1.6 MHz. A play around with my function generator (non-contact via a coil loop) reveals that AM IF is at 455kHz, but rather dead. Even more deaf when I tuned the function generator to 525 kHz to 1.6 MHz. AM RF alignment appears to be spot-on. Curiously, with the function generator set to 1.6 MHz, I can receive the signal on the radio at three places on the dial. I assume that, because I had to turn the generator output up ridiculously high to obtain a hearable result, I'm overloading the mixer and getting third order mixing products.
So that's as far as I've got: FM seems to be working fine. AM oscillator is working, but something's not right along the IF. I hope someone might find this interesting, and I'd love to know anything about those RF transistors if anyone's seen them before.
My name is Steve, but I answer to most things like "Oi, you!".
