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Philco 91-221 antena transformer primary - Printable Version

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Philco 91-221 antena transformer primary - rickd - 03-11-2014

Looks like this puppy has a burned up primary (lightning strike perhaps) Anyone have any idea how many turns on this? How critical?
Also wondering why there is a resistor paralleling the coil.
http://www.nostalgiaair.org/PagesByModel/658/M0029658.pdf

All opinions welcomed.

RE: Philco 91-221 antena transformer primary - morzh - 03-11-2014

Ah!

I think someone decided to use an outlet Hot as an antenna.
Lightening is also a possibility.

I dealt with this exact problem in the Emerson I restored this summer.

I was able to count my turns though when unwinding the coil.
It is bakes so badly you are not able to try to unwind it and count the turns? I you are off by a few turns it does not matter much.
In my case it was about 200 turns.

RE: Philco 91-221 antena transformer primary - skyscraper - 03-11-2014

The Philco Repair Bench site suggests dragging a safety pin over the windings and listening for 'clicks.' It's worked well for me, even on completely disintegrated coils.

I don't know exactly what the resistor does electrically, but from my experience with crystal radios, about 1k stops low frequency AC hum from getting to the detector. Just a thought.

RE: Philco 91-221 antena transformer primary - rickd - 03-11-2014

Thanks for the reply's.
Tried counting the turns, apparently somewhere in excess of 220, guess about 250. Lot of it came off in pieces, wood core is charcoal. Right now thinking about trying a similar looking coil from a donor 60 antenna transformer with the green disease on both solenoid windings. The coil I need was mounted inside the tube and looks good.

RE: Philco 91-221 antena transformer primary - morzh - 03-11-2014

The number is plausible, as I said in my cae it was close, as I remember it, 230 or so

RE: Philco 91-221 antena transformer primary - Steve Davis - 03-12-2014

You can use a plastic sewing machine bobbin as a form to wind a new one. See my post in this thread http://www.philcoradio.com/phorum/showthread.php?tid=8833

Steve

RE: Philco 91-221 antena transformer primary - rickd - 03-13-2014

Just an update, the coil from the Philco 60 antenna xfmr (along with the always needed oscillator cathode winding rewind), and everything is working great. Interesting set.

RE: Philco 91-221 antena transformer primary - morzh - 03-13-2014

Well, praise the Lord and the spare chassis!

RE: Philco 91-221 antena transformer primary - Joeztech - 03-23-2014

In answer to your question about why a resistor is bridged across the coil or primary of the RF input transformer, this is usually done to broaden the bandwidth of a coil/transformer assembly. Sometimes coils or transformers have high enough Q that they tend to tune rather sharply to a small range of frequencies. A resistor can be bridged across the coil or transformer winding and the result it a much broader bandwidth. On an RF input, this helps keep the signal sensitivity from low to high frequencies pretty nearly equal as the radio is tuned across the dial.

Joe