[Boatanchors] Testing a crystal

[Bry Carling]

Yes Gary this is quite correct. That is the same technique we used for manufacturing crystals at Cathodeon Crystals when I was working there in the 1970s. The lapping machines would be connected to the antenna terminals of an Eddystone receiver directly. You could hear the whole group of Crystal blanks “singing“ and the frequency would rise across the dial as the grinding paste ground them higher and higher in frequency.
It is quite a wonderful process.

Best regards - Brian Carling, AF4K CRYSTALS

http://af4k.com


On Jul 8, 2018, at 1:23 PM, Gary Peterson <kzerocx at rap.midco.net<mailto:kzerocx at rap.midco.net>> wrote:

This reminds me of something I read in Hints & Kinks in a 1930s QST.

The piece said that a crystal could be tested by placing its pins in series between a random length antenna and the antenna terminal of a receiver.  When the receiver is tuned to the resonant frequency of the crystal, there is an obvious change in the sound of the random noise coming out of the speaker.

I mentioned this to a friend at coffee one evening.  He was skeptical.  We went to his QTH and he brought out a box full of crystals and some clip leads.  By golly, it worked.  The noise sounds just like what happens when you kick in a crystal filter in the IF of a receiver.  This seems to be a stress-free method of measuring the approximate frequency of a crystal.  Obviously, its exact frequency will depend on circuit parameters.

Gary, K0CX

“Note that the Q of the crystal is so high that you will not be able to
'land' exactly
on it unless you are using a digital signal generator (and you may have to
watch
the scope trace very closely to see the blip).
ian K3IMW”
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