Zenith AM/FM radio loses signal.

Originally Posted by Charlie

Sounds like you have a capacitor changing values as the set warms up. Does it ever get to the point to where it doesn't drift anymore? It could also be tube, which of course would be easier to change... possibly the oscillator.

Hey Joe... how did you make out with your 1955 Motorola? Hadn't seen you around for a while, and I've been wondering about it.

Charlie,
Thanks for the suggestion. As to the status of the '55 Motorola, I've discovered the flyback transformer is going bad. I'm currently working with a gentelman named John Horvath at Amptech systems to try to locate either a replacement (not likely to find one), or someone who can rewind the old transformer. So far, no luck.



Joe

[Chad Hauris]

I would replace the selenium rectifier in the power supply with a silicon diode with a 50-100 ohm 10 watt resistor in series with it. Was working on a Magnavox 50's FM set that would not tune above 98 mhz and the FM sensitivity was really poor: replaced the selenium with new silicon diode and performance is much better.

[Nick_the_'Nole]

I have one with the same chassis that was doing the same thing. I replaced one of the tubes, I think it was the 12AT7, and the problem went away completely. Also seems to pick up stations clearer now, but that might be my imagination...

Originally Posted by Nick_the_'Nole

I have one with the same chassis that was doing the same thing. I replaced one of the tubes, I think it was the 12AT7, and the problem went away completely. Also seems to pick up stations clearer now, but that might be my imagination...

Thanks for the suggestion. I replaced it with a new production Ei 12AT7 tube and the problem has gone away completely.


Looks like I'm back in business.



Joe

[Jeffhs]

Originally Posted by Chad Hauris

I would replace the selenium rectifier in the power supply with a silicon diode with a 50-100 ohm 10 watt resistor in series with it. Was working on a Magnavox 50's FM set that would not tune above 98 mhz and the FM sensitivity was really poor: replaced the selenium with new silicon diode and performance is much better.

Chad, I have a 1963 Zenith radio with a selenium rectifier. The set still works well, no problems (yet) with the rectifier or anything else. Sensitivity is great, it sounds fantastic, so I really don't want to go into it unless I have to. What could go wrong with a selenium that has been working well for 41 years, no problems? I would think if the thing hasn't shorted by now, it should go for years. I always thought the only way seleniums ever went bad was if they were accidentally shorted (as you once mentioned happened to a Zenith radio you had, in which a headphone jack worked loose and fell on the stack); never thought they could short or open on their own.

I have heard when they start to go bad they smell like rotten eggs or burning sulfur. Never smelt one this bad, but I do agree they should be upgraded with silicon.