"Deek" wrote in message
. ..
yea right wrote:

SNIPPED

It says filter. Here is a much better picture..
http://www.vambo.org/tmp/Hallicraftt...stalFilter.jpg


Yep! It is a single 455 KHz crystal in a standard FT-243
[if I recall correctly] size case.

This type "filter" is very common in radios well into the
60s. It is used in it's series resonant mode in the first
455 KHz i.f. amplifier tuned circuit. The technique did a
fairly good job of sharpening the selectivity of the older
moderately priced AM type receivers.

Also in higher priced receivers like the SP-600-JX and
51-J series, they work quite well for CW. The original idea
was patented by James Lamb around 1935 and applied first in
National Co's receivers, for instance the famous HRO. A
later version was patented by Hammarlund (can't remember the
inventor's name) and used in their receivers (Super-Pro 100,
200, 400 and others) and some others. The filter in Collins
receivers is of this type. The Hammarlund version allowed a
wider range of bandwidth and also adjustment of the notch
without changing the center frequency. Hallicrafters applied
the Lamb type to all their receivers with an X in the type
number, i.e., SX-28. Earlier crystals were often mounted
between clamps as in the Hammarlund Super-Pro, later
versions were in standard type crystal cases like this one.
Single crystal filters do not have very good skirt
selectivity and were supplanted by various types of
multiple-pole IF filters when methods of producing these at
reasonable prices were developed, and T-type notch filters
operating at the RF frequencies.
The crystal has slightly different characteristics from
those designed mostly for use in oscillators.
I don't know what Hallicrafter's receivers this crystal
fits but there is likely someone out there with a receiver
that needs the crystal.


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Richard Knoppow
Los Angeles, CA, USA