"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