"Rubber Crystal Holders"

[Glen Zook]

I have been asked to manufacture a "kit" to convert
"standard" FT-243 crystal holders so that the
frequency of the crystal can be varied.

The principle behind this is that by varying the
pressure on the crystal itself, the oscillation
frequency will change.  The amount of change is
dependent on the individual crystal.  Some crystals
will move 2 or 3 KHz at the fundamental and other
crystals will move only a few hundred HZ (if that).
You just have to find out by trial and error.

During the 1930s and 1940s, such "rubber crystals"
were available commercially.  By the mid-1950s, most
of the manufacturers who had been making these either
discontinued them, or, the entire company went out of
business.

The "kit" would actually be a complete assembly
consisting of a "new" plastic cover for the FT-243
crystal holder.  This cover will have a nylon machine
screw threaded through the center with a knob.  You
would remove the existing crystal cover, replace with
the new one, and gradually tighten the knob / screw
combination until the crystal starts to work.  Then,
by varying the pressure on the crystal, the frequency
will change.  The only thing is that you must be
careful not to apply too much pressure and fracture
the crystal.

By using nylon, it will require more pressure to
fracture the crystal and there would be no problem of
the possibility of the crystal not oscillating due to
additional metal.

Of course, as the frequency is multiplied (i.e. using
a 40 meter crystal on 15 meters) the amount that the
frequency will be changed will increase.

As with most of the things that I have been making for
the "boat anchor" crowd, the cost of materials will
not be that great (under $2 most probably).  The cost
comes from the labor involved.  So far, I haven't made
any of these for "consumption".  If there is any
interest, please let me know.

Right now I'm thinking in the neighborhood of $15 to
$20.  But, if the interest is there, and if I can get
some sort of "production line" going, then the cost
could drop to the $10 to $15 range.

Please let me know if you have any interest in this.

As I said above, some local amateurs have asked me to
produce these "rubber crystal" holders.  I am not sure
if it will be worth all of the trouble to make the
"jigs", etc., necessary to make these.  However, I'm
"testing the waters"!

Glen, K9STH

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