FT 243 Sandwich Crystals Needed.

[Bry Carling]

> I wonder.. and I've never order any crystals from Bry, but I kinda of  
> wonder if the "modern tiny crystals" have enough hummph to keep them  
> from shattering when used with an old cathode keyed novice  
> transmitter like the DX20 or something like it?
> 
> 
> mike

Hello Mike - they are in use in hundreds of ham transmitters and 
generally do not fail.

Some extensive tests were done by materials science 
professor, Dr. David Gordon-Smith, G3UUR a couple of 
years ago and documented in Electric Radio Magazine.

He took them to the limit and found that in some cases 
the newer crystals hold up BETTER than the old, larger 
WW2 elements. It is usually the connection to these crystals 
that will fail if you subject them to excessive crystal currents,
not the quartz itself. It is wise to limit crystal current to 
a maxiumum of 40 mA with any crystal in any circuit and 
there are tried and true methods for doing that if you are 
concerned.  One of these is a small pilot light bulb in series 
with the crystal. For more details, see:

http://www.af4k.com/crystals.htm

All the best - Brian

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