"k3hvg" wrote in message
...
If I could have said it all in one
message...................

The contract info on mine says:

ORDER No. 25557-PHILA-49-7C.

Looks like it would be 1949 for this one.......

There is a list on one of the Hammarlund sites with a
list of military contracts for the R-274 on it. I don't know
when the earliest order for the Hammarlund version was put
made.
About the crystal filter: Hammarlund owned the patent
for the version of the filter used on its receivers and,
later, by Collins and others. The original Lamb filter had
problems with broadening it out, it tended to shift center
frequency, and the notch was not symmetrical. Hammarlund's
version allowed broadening out enough to use on phone and
had pretty constant gain. Also, the use of a double phasing
capacitor allowed keeping the peak centered when varying the
notch frequency. In general T-notch filters work better but
the crystal was the best available at the time.
The Hallicrafters S-73 looks well worked out. I think
they simplified the turret contact arrangement quite a bit
but I don't know how well it works in practice.
Hammarlund made the mistake of taking Sprague at their
word about _Black Beauty_ caps. These were _supposed_ to be
deluxe, low leakage caps with a wide temperature tollerance.
The dielectric as a combination of paper impregnated with
plastic. They _should_ have been very long lived and of
good performance. Unfortunately, something went badly wrong.
My own suspicion is that the casing material had some
serious problem. Many of these caps are found split and not
just at the mold seams. The caps inside are distorted in
shape. Of course, I don't know that they were wound round
originally but the bad ones are flattened in various ways, I
suspect distorted by the shrinkage of the case. Sprague also
made a similar cap with radial leads called an "Orange
Drop". These were dipped in epoxy rather than being molded
in whatever was used for the BB caps. I've never heard that
these were particularly trouble prone. BB caps were used in
some very deluxe equipment such as instruments made by
General Radio and Hewlett-Packard. I first heard that they
were bad guys when I was a teen ager so the problems must
have shown up pretty quickly. I don't think all BBs are bad
becuause Sprague continued to advertise them after the time
the military issued the MWO for chaning out all of them in
the SP-600. There are probably people who know first hand
what happened.
There sure are a lot of questions about old equipment
which were probably answered in the manufacturing data but I
doubt if much, if any, of that exists because most
businesses see keeping historical records as unprofitable
and return on investment is what makes the world go 'round.


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Richard Knoppow
Los Angeles, CA, USA