06-27-2021, 10:31 PM
I made up a harness for the speaker, sorted out what was transformer and field coil from the wires on the speaker and spliced the two together. At the other end, a 5 pin plug was connected. I made some last checks and got ready for testing. The usual procedure - no tubes, "dim bulb" tester was an instant pass. I checked voltages on the transformer secondary and all was well. No noises save a smooth and very feint hum. Then all the valves/tubes except the rectifier. The bulb lit up, then faded to very dim - All good. After that I put the 5Y3 in it's socket, with a meter connected to B+ and applied power.. Voltage came up, and there were some sputtering sounds from the loudspeaker - Life! Crackly bit there. Quite a bit of crackling. More crackling if the bandswitch was operated. All good signs. Although there was not an antenna connected at this point, I tried tuning on the MW band anyway, and found a station. Excellent.
The terrible garage antenna was hooked up and more stations could be found, but there was still a lot of intermittent crackling and not much volume at all. I tried powering without the bulb, but although there was static, no stations resulted. There was also still the issue of crackling, so I turned it off, and removed each valve, cleaned pins and sockets, and cleaned the bandswitch. Things came back better, but still crackly, and still better on reduced power, so I turned the chassis over, and started poking carefully with an insulated stick to see if the crackle could be provoked. As various parts were prodded, there was not much response, but all of a sudden, it went dead...
OK, time to consult the voltage chart... and I already had a suspicion which turned out to be valid. The 11 KOhm section of the candohm, which is the bulk of the resistance between the HT and the rest of the chain had opened. Temporarily, I added a 1W, 12K resistor across the tags, and life was restored. After cleaning the bandswitch, there was more life evident on the SW bands, and I caught snippets of a broadcast station, and the WWV Time Signal - I think 10 MHz, but without the dial, hard to say.
Last of all, the signal generator was tuned up to 252.5 KHz and the IF transformers were aligned. They were quite a bit off-peak, and this obviously brought sensitivity up considerably.
So, a good day on the radio bench
The terrible garage antenna was hooked up and more stations could be found, but there was still a lot of intermittent crackling and not much volume at all. I tried powering without the bulb, but although there was static, no stations resulted. There was also still the issue of crackling, so I turned it off, and removed each valve, cleaned pins and sockets, and cleaned the bandswitch. Things came back better, but still crackly, and still better on reduced power, so I turned the chassis over, and started poking carefully with an insulated stick to see if the crackle could be provoked. As various parts were prodded, there was not much response, but all of a sudden, it went dead...
OK, time to consult the voltage chart... and I already had a suspicion which turned out to be valid. The 11 KOhm section of the candohm, which is the bulk of the resistance between the HT and the rest of the chain had opened. Temporarily, I added a 1W, 12K resistor across the tags, and life was restored. After cleaning the bandswitch, there was more life evident on the SW bands, and I caught snippets of a broadcast station, and the WWV Time Signal - I think 10 MHz, but without the dial, hard to say.
Last of all, the signal generator was tuned up to 252.5 KHz and the IF transformers were aligned. They were quite a bit off-peak, and this obviously brought sensitivity up considerably.
So, a good day on the radio bench
I don't hold with furniture that talks.
