radio-shac: Bad LO coil

Fellow radiophiles,

I have a special fondness for Radio Shack's first house branded Realist tuner. Now I own two of these tuners. This is quite unusual for me. The first tuner had been somewhat modified in that the phono pass-through connection was removed. When I came across one of these tuners at a low price with the very rare wooden case, and the original circuitry, I decided to buy it.

But this "original" condition set had serious trouble at the LO (Local Oscillator). There were portions of the tuning band where it would completely fade out. After comparing my two tuners, I noticed a slightly different LO and RF coil design for the two tuners.

The new tuner with the faulty LO:

The old tuner with a good working LO:

The new tuner with a new 3 turn LO coil:

The LO now works fine with the new 3 turn coil. The coil was bent in place for correct alignment at the low end fo the dial. The existing trim capacitor in parallel with the LO coil was used to align the high end of the dial.

In a way, I was lucky to have to sets to compare. Perhaps the old coil was original, and someone added the capacitor at the tap. I don't remember if I removed the cap to see if that was the cause of the LO trouble. I reasoned that the LO dropouts might have been caused by a lower Q in the 4 turn coil that was scrunched against the chassis. I will never know for sure what was the real cause: bad coil design, or spurious capacitor.

Regards,

-Joe

 

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