07-01-2018, 10:49 PM
Thanks Arran & David.
I missed your posts (busy day) but have made a lot of progress.
One thing early on I noticed was that the feed to the tone switch, strapped across an unused pin on the 6F6 socket changed hum when "poked about". I had to extend the wires of a capacitor to make this connection, and the wire extension had broken, hidden by the sleeving I had used in the interest of neatness and safety.
Restoring this (Really... and after all the time I spent cursing the bad repairs of others), I found that there was some activity on bands B and C . Now there's progress.
Noise, but nothing sensible on the 31 m spread band and still nothing from the broadcast band.
Then I set about trying to set about tuning in the IF. Alas, my sig gen is very noisy and unmodulated - making it extremely hard to determine the fundamental from the hash. Instead, I found a station, and using an accurate radio, found the oscillator frequency. Then I adjusted the oscillator to the correct 455 kHz offset, and brought the IF back in to line. I do wonder that there is something amiss in the second IF transformer (mica caps?). When I was trying to do this with the signal generator, it was quite easy to get a nice peak at 460 kc, but very hard to tune it down. Perhaps something to revisit?
Anyway, still troubled by the lack of basics, such as the main 550 - 1400 kHz broadcast band, I started some diagnostics, and found that the oscillator coils for this band are open. A little investigation found a broken wire at the earthy end of the coil that is likely the culprit, but at this point, other duties beckoned me away. I will join the ends and see what this accomplishes, and then decide if a re-wind is in order.
No clue on the 31 m band or the preset tuning yet, but I suspect all will fall in to place with some more investigation. Oh, and the 6-18 MHz bans drops out around 7 MHz - for some reason the oscillator dies, but is active either side of the dead spot. As one tunes, the set loses sensitivity gradually before dropping out, then fading back in.. Strange!
So, I am happy to say the RCA is stumbling back to life, and there is more to do.
Cheers
Ed
I missed your posts (busy day) but have made a lot of progress.
One thing early on I noticed was that the feed to the tone switch, strapped across an unused pin on the 6F6 socket changed hum when "poked about". I had to extend the wires of a capacitor to make this connection, and the wire extension had broken, hidden by the sleeving I had used in the interest of neatness and safety.
Restoring this (Really... and after all the time I spent cursing the bad repairs of others), I found that there was some activity on bands B and C . Now there's progress.
Noise, but nothing sensible on the 31 m spread band and still nothing from the broadcast band.
Then I set about trying to set about tuning in the IF. Alas, my sig gen is very noisy and unmodulated - making it extremely hard to determine the fundamental from the hash. Instead, I found a station, and using an accurate radio, found the oscillator frequency. Then I adjusted the oscillator to the correct 455 kHz offset, and brought the IF back in to line. I do wonder that there is something amiss in the second IF transformer (mica caps?). When I was trying to do this with the signal generator, it was quite easy to get a nice peak at 460 kc, but very hard to tune it down. Perhaps something to revisit?
Anyway, still troubled by the lack of basics, such as the main 550 - 1400 kHz broadcast band, I started some diagnostics, and found that the oscillator coils for this band are open. A little investigation found a broken wire at the earthy end of the coil that is likely the culprit, but at this point, other duties beckoned me away. I will join the ends and see what this accomplishes, and then decide if a re-wind is in order.
No clue on the 31 m band or the preset tuning yet, but I suspect all will fall in to place with some more investigation. Oh, and the 6-18 MHz bans drops out around 7 MHz - for some reason the oscillator dies, but is active either side of the dead spot. As one tunes, the set loses sensitivity gradually before dropping out, then fading back in.. Strange!
So, I am happy to say the RCA is stumbling back to life, and there is more to do.
Cheers
Ed
I don't hold with furniture that talks.