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Old 08-14-2020, 10:56 AM
nasadowsk's Avatar
nasadowsk nasadowsk is offline
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Join Date: Jul 2004
Location: Catawissa, PA
Posts: 936
RCA CTC-4: dead front end :/

Ok, I've gotten my 4's basic stuff working, except the front end. Inject into the IF isn't doing much, the tuner isn't doing squat. It's intermittent (sometimes), though, but more 'not working' than 'working' Which is annoying.

I'm not sure where to look - voltages seem fine, the service manual naturally doesn't say what the AGC range is, the Sams resistance check seem fine...

I an re-check the tuner and if strips, but I dont' seem to be getting anywhere.

Oddly, when it powers up,you hear what almost sounds like the sound going through the FM band quickly.

There some secret about these sets that I'm missing?
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Old 08-14-2020, 03:28 PM
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Electronic M Electronic M is offline
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Join Date: Jan 2011
Location: Pewaukee/Delafield Wi
Posts: 14,758
If injection IF signal into the IF circuits isn't giving you signal then your IF is defective and you should worry about your IF before you even look at the tuner.

One of my CTC4 sets the alignment was abominable...sound, luminance and color could all be obtained with fine tuning adjustment, but I could only get one at a time depending on adjustment....the IF adjustments were fine and it was a resistor problem...I unsoldered one end of EVERY IF resistor and changed every one that was off tolerance or borderline and the IF started working like new.
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Old 08-14-2020, 04:04 PM
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zeno zeno is offline
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Join Date: Mar 2013
Location: New Hampshire
Posts: 4,672
Tom has a good start. A good running set without any signal should
give you strong snow & a nice water fall of audio noise. AGC can be
substituted with a little bias box. AGC problems were quite rare. almost always
IF problem gives bad or no snow & washed out pix. I would NOT consider
IF alignment at this point & if you get there replace ALL IF tubes with
brand name NOS tubes first. The 4.5 & 41.25 ( IIRC) can be touched up
after the set is strong. Just flag your diddle stick so you can go back.

73 Zeno
LFOD !

BTW if you have an IF generator you can walk through the IF stages.
Another great little tool is a tuner subber. Strip a click tuner out of
a junk solid state set. Give it B+ & a voltage divider for AGC. Short
the AFT line to ground. All works on batteries OR get one off Ebay !
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