[Milsurplus] [Boatanchors] Hallicrafters Crystal Polarity?

[Michael Bittner]

----- Original Message ----- 
From: "Dbarms via Boatanchors" <boatanchors at mailman.qth.net>
To: <Boatanchors at mailman.qth.net>
Sent: Tuesday, March 19, 2019 12:33
Subject: [Boatanchors] Hallicrafters Crystal Polarity?


> My downloaded copy of the Hallicrafters SX-28 Instructions Manual says 
> "mounting the crystal prevents possible change in polarity which would 
> occur if the crystal were improperly inserted into the circuit." This 
> concerns the crystal in the IF crystal filter circuit and explains some of 
> why permanently mounting the crystal is better than using a socket. I 
> didn't think crystals have polarity. I have an SX-28 carcass from which I 
> removed the 455 kHz crystal for placement in a SX-62 I am working on which 
> the crystal stopped working. No polarity markings on either one, and they 
> share the same Hallicrafters part no. Thanks!
> - Dave

Dave,
The only thing I can think of is that there may be different stray 
capacitances between the two sides of the "specially designed polystyrene 
holder" that could unbalance the filter circuit.  Probably the use of the 
word "polarity" in the manual is just a short hand way of referring to this 
capacitance effect.

I am interested in hearing any further thoughts on this topic as I am 
presently working on a homebrew receiver based on the AN/GRR-2 (military 
SX-28-A).  It will use an original Hallicrafters 455 kHz plug-in crystal in 
a circuit using Meissner crystal filter transformers.
Mike, W6MAB




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