Noise when tuning in/through signal

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Edward Cain:
Thanks for all the suggestions guys. And I take to heart the advice of a few caps at a time.

Carl asked what the audio was like with no/weak signal. With no signal I have just barely audible background noise. With weak signals I just have weak audio and some background noise but don't notice the same symptom that prompted my question.

I looked at the manual for Hallicrafters' alignment instructions and I'm a bit confused. For the IF alignment it tells me to set my signal generator to approximately 455 kHz and proceed to adjust slugs for maximum output. I assume they're talking about audio output. Am I correct? They make no mention of a modulated 455 kHz signal.

   In any event, I haven't yet aligned it cause I've found that I don't seem to have output from the bfo. I'd like to solve that problem first, since bfo signal is part of the alignment procedure.
   I'll start another topic for that problem.

Thanks,
Ed

k4kyv:
Quote from: flintstone mop on April 03, 2010, 09:12:23 AM

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 would say it's the wiper contacts on the tuning capacitor.  I had the same  thing with my NC-173 years ago.  It was only noticeable with strong carriers in AM mode.  It didn't show up in CW mode with the BFO on.

I could spray it with contact cleaner and that would clear up the problem for short while, but it would soon start back again.  Try a small dab of WD-40.  I have found that to work better contact cleaner. Another substance that works is called Electro-clean. It is a degreaser, and the can says it is for cleaning motor brushes and other electrical equipment.  If the contacts are really dirty, maybe try that, then lubricate with WD-40.

I had a noisy AF gain pot on my 75A-4.  Contact cleaner would stop the problem for about 3 days.  Later on, I tried WD-40 and that fixed it for good; the problem never came back again after several years of use.

w3jn:
THe proper way to clean the contacts on a tuning capacitor is to wet some bond paper with DeOxit, then pry the wiper up VERY gently just enough to slip the paper between the contact and the capacitor rotor.  Move the cap thru its motion as much as you can.

This can also resolve drift problems.

The SX-62's FM IF isn't 455 KHz, it's 10.7 as I recall.  The 455 KHz IF is for the lower bands, and non-FM.  You'll see that the 455 and 10.7 IF transformers are kind of in series; the 10.7 IF has essentially no effect on the 455 IF.  Still, align the 10.7 IF first, then go after the 455.

w1vtp:
Quote from: Pete, WA2CWA on April 01, 2010, 08:11:17 PM

Personally, I never replace any components until I know what problems I'm trying to fix.

Anyway, noise, in AM mode, FM mode, all modes? Did you put a scope on it at any points in the circuitry?


Yep!  Muddies up the water, I think.  I think a good visual for swollen lytics and a thorough check with a Simpson 260 (good analog multimeter)

That said, the guys here will be very helpful, I'm sure

GL, Al

flintstone mop:
Quote from: k4kyv on April 03, 2010, 11:49:30 PM

Quote from: flintstone mop on April 03, 2010, 09:12:23 AM

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 would say it's the wiper contacts on the tuning capacitor.  I had the same  thing with my NC-173 years ago.  It was only noticeable with strong carriers in AM mode.  It didn't show up in CW mode with the BFO on.

I could spray it with contact cleaner and that would clear up the problem for short while, but it would soon start back again.  Try a small dab of WD-40.  I have found that to work better contact cleaner. Another substance that works is called Electro-clean. It is a degreaser, and the can says it is for cleaning motor brushes and other electrical equipment.  If the contacts are really dirty, maybe try that, then lubricate with WD-40.

I had a noisy AF gain pot on my 75A-4.  Contact cleaner would stop the problem for about 3 days.  Later on, I tried WD-40 and that fixed it for good; the problem never came back again after several years of use.


ME 'N' Don seem to be on the same channel for the problem of scratchy whilst tuning. How does the noisy I.F. enter into making noise whilst tuning said tuning condenser??
Fred

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