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#7
November 16th 07, 10:15 PM
posted to rec.radio.amateur.boatanchors
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BC-453 IF tuning
"Uncle Peter" wrote in message ... "Richard Knoppow" wrote in message ... It isn't the Q but rather the mutual coupling between primary and secondary windings. Hammarlund had a patent on this kind of transformer which it used in the Super-Pro series of receivers. In the Super-Pro two of the IF transformers have movable coils which are controlled via cams operated by the selectivity knob on the front. Richard Knoppow Los Angeles, CA, USA Some Silvertone 1930s vintage consumer radios have the same arrangement. Pete Hammarlund used to offer adjustable IF cans as stock items. I have somewhere a circuit for a high fidelity AM receiver using a couple of them. I didn't know any home type sets were made with them. The advantage of the Hammarlund arrangment over the tapped terciary coil system used by Hallicrafter's and some others is that the pass band stays symmetrical about the center frequency. In some other arrangements the bandwidth expands in only one direction. The SP-600 uses a tapped coil arrangement which does not have this problem and also expands symmetrically. -- --- Richard Knoppow Los Angeles, CA, USA |
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