RCA 8x71

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RCA 8x71

Post by lowell on Thu Feb 19, 2009 3:51 pm

I am fixing this radio and so far have gotten it to power up, and then begin to receive stations. However I tried to adjust one of the IF transformers and I lost all my sound. The transformer in question is 970435-4. One is 455 pri and 10.7 sec, and the other is 10.7 pri and 455 sec. Does anyone know if I will be able to find a suitable replacement. I have read about bypassing them on another website. Your thoughts please.

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Re: RCA 8x71

Post by Johnnysan on Fri Feb 20, 2009 3:47 am

I'm having a little difficulty with your thread. The IF transformers are separate for FM and AM; you will not have one frequency at the primary and another frequency at the secondary. I think your confusion is because these are mounted in the same housing. Note: the same TYPE transformer is used for the 1st IF of AM and FM, and the same type for the 2nd IF of AM and FM. Also, the RCA part number for the 1st IF is 73745; 2nd IF is 73974.
If the transformer has opened up, you should try taking it apart to find the break if possible. The resistance of the coils will be from .3 ohm to about 12 ohms, depending on what coil you are measuring. Also, if you lost all sound (both on AM and FM), you probably don't have an IF problem. Do you have the Sams information and have you re-cappped the radio?

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Re: RCA 8x71

Post by lowell on Fri Feb 20, 2009 1:44 pm

hello yes radio was recapped and that helped a lot. Then I tried adjusting the transformer screws w/ a screwdriver and it made a very light cracking sound (not through the speaker) and the sound cut out and we've yet to be able to get any sound now. I guess I'll open the transformer up or take a measurement and see.

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Re: RCA 8x71

Post by Terrible Terry on Fri Feb 20, 2009 2:33 pm

These I.F. transformers appear to be the kind that have the adjustable ferrite cores rather that adjustable capacitors. The ferrite material is rather brittle and it is possible the cracking sound you heard was the ferrite core breaking. This is fairly common when the core gets stuck and is over-torqued. It would then make it impossible to retune the transformer to the proper frequency. I seems likely that it would only effect one band though, the AM or the FM, depending on which one broke. It's sometimes possible to remove the core parts and simply glue them together and reinstall them.

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Re: RCA 8x71

Post by lowell on Fri Feb 20, 2009 3:29 pm

ok I'll check into that... thanks!

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Re: RCA 8x71

Post by VANT on Sat Feb 21, 2009 12:04 pm

http://www.oldradioz.com/john/Tech/IFcapRepair.pdf

DOES THIS HELP?
---VANT
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rca

Post by lowell on Mon Feb 23, 2009 4:48 pm

so I took the transformer out and tested all the coils and caps and nothing was wrong with it. How do I now tune the transformer properly using the set screw/ferrite cores.

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Re: RCA 8x71

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