[Milsurplus] FT-241 surplus LF crystals chan - freq list ?

[David Stinson]

ent through a great many crystals a couple of
years ago.  Found that many-

especially those in large, Bakelite holders,
suffered from various levels of 

chemical deposits on the blanks and electrodes.
The gunk was caused by 

out-gassing of volatiles from the case materials-
Bakelite, plastic, rubber etc. 

that settle inside the crystal.  A Q-Tip soaked in
Naphtha (Rohnson 

Lighter Fluid) swabbed on the inside surfaces
comes away with

these deposits.    Had some success cleaning
everything with 

Naphtha, but a few old large-blanks that had been
hand-ground 

appeared to have the deposits so deep in the
surface that even soaking

them for a couple of weeks would not remove it
all.

 

"Plated" Crystals: 

Learned the hard way:  you've probably seen
crystals that have the 

silvery plating on each side of the blank.  The
thickness of this plating

is carefully controlled to set the blank on
frequency.  If you put one

of these (HF) crystals in etching solution, it
eats the plating rapidly 

and the crystal will move several KCs in seconds.
When I try to move

one of these, typically immerse the blank in the
etchant for 3 seconds

or less, then into the rinse bath.   One can
over-shoot easily.  

Haven't tried to fine-adjust one yet but I might
try using a Q-Tip

to put etchant just on the plating for a brief
time and see if the

freq movement is more easily controlled.

One "up-side:"  the plated crystals seem to take
"penciling down"

better than others.

 

Disclaimer:  I haven't tried to etch FT-241
crystals.  I don't know

if all of mine are "bad" or if I just don't know
the proper oscillator

to use with them.  Anyone got a simple test
circuit?

 

73 Dave AB5S

 

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