Flawed IF Transformer in an AA5

[Winky Dink]

I’m redoing some of my early projects, starting with this Farnsworth AA5. Below is the 2nd IF transformer.



I’m guessing that the discrepancy in resistance is due to oxidation under the circled, light-colored area. The radio had been working with a ripple in the audio, and I haven’t yet done any realignment.

I’m going ahead with the re-restoration, but I’d like to know if I should anticipate any problems due to the flawed IF transformer.

I would greatly appreciate your advice.

[wa2ise]

That coil may use litz wire. Litz wire is like stranded wire, except each strand is insulated. Reduces skin effect at RF. What I'm leading up to, is maybe one or two of several strands are broken, and that would result in a higher resistance reading. It would reduce the Q of the circuit, but that might not be worth worrying about, it could be a feature even, making for wider bandwidth of detected audio signal.

[Winky Dink]

You're right about the Litz wire. I hadn't thought about it, but at the solder connections some of the wire is separated into very fine strands, and there are also loose threads of insulator. I remelted the solder connection and also scraped the wire close to the coil to get the most accurate measurement, but it always came out to 38 ohms.

Thanks.

[old_coot88]

There's always the handy dandy 'aspirin trick' for stripping hair-fine wire without mechanical scraping. Scroll down to post# 26..
http://videokarma.org/showthread.php...hlight=aspirin
It should work fine for litz wire too.

[Winky Dink]

I hadn't thought of that, but I do remember reading the post. Thanks.