Noise when tuning in/through signal

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w3jn:
Carl, I've gone thru probably 10 or more SX-42s and 62s, and only one had the bad silver micas in the IFs.  I have heard of a couple other cases though.

However I had the same issue with a '43 vintage SX-36.... no peaks in the IFs.

In any event nobody is suggesting this be done without first verifying it's the problem.  It's a big PITA and unless you're careful, you can damage the IF xformers in the process.  I made the mistake of trying to unslobber the micas.  Made a mess and damaged the litz wire... subsequent caps were just clipped out and the replacements soldered to the old pigtail remnants.

flintstone mop:
IF the scratchy sound is WHILE tuning THEN it could be the variable capacitor that needs to be looked at. The plates might be rubbing together at certain points of rotation or the stator contacts need cleaning.
I assume that this RX uses a variable cap to change freqs and shift the LO during tuning. Not familiar with the circuitry.

Fred

KM1H:
Ive done around the same number John and havent had a noisy IF yet. I also wonder if Halli went with the deposited silver substrates around 51-52 when it pretty much became an industry standard? They bought from the same suppliers, unlike National, Hammarlund, etc.

Carl

w3jn:
Symptom wasn't noise crashes in the IF on mine, Carl, there was just no gain in the IF section and the xformers wouldn't peak.  They were discrete mica caps, not those deposited jobs you see in consumer BCB radios.

WQ9E:
JN,

I found that problem in one of my SX-62 receivers with exactly the symptoms you describe but that was the only regular IF mica I replaced.  But the FM discriminator problem with mica caps was very different in my experience.

I am not sure why the problem seems so severe with the discriminator transformer.  It may be that it is far more sensitive to the drop in Q caused by slight leakage while this same level of leakage in the 10.7 Mhz. IF transformers may slightly drop the gain and broaden the response.  If this effect is minimal with slight leakage it wouldn't be obvious without making measurements.  In any case, every Halli I have in the 42/62 family (including the distant cousin S-36A with 5.25 Mhz. IF) required replacement of leaky caps in the discriminator to achieve reasonable performance.  The S-36A is actually the best performer I have-after 10 minutes warm up there is no discernible drift in the HFO or discriminator tuning on the FM BCB.

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