[Hallicrafters] Piesoelectric effect case in point.

[Troglodite at aol.com]

In a message dated 1/3/2011 9:27:03 A.M. Central Standard Time,  
rbethman at comcast.net writes:

It is two slabs of rochelle crystals that are anchored at one end, and a  
lever from the diaphragm attached to the opposite end.

I wonder why  these hold up so much better than Astatic's elements?

I can only surmise  that it has to do with the support system being so 
isolating, and made of  rubber.
 
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The problem with the "crystal" microphones  that use Rochelle salt elements 
are not mechanical, they are thermal. Leave them  in an automobile on a hot 
day and they are gone. The crystals either crack or  melt, I have never 
investigated which, but they cannot stand heat. Ceramic  microphones do not 
have this particular problem.

Used indoors in normal  conditions, the old Astatic microphones last for 
years. I have one that still  works fine. But expose them to heat and they are 
gone. Same thing for the  phonograph cartridges. If either needs to be 
transported through a high heat  environment, they need to be thermally 
isolated, like in a thermos bottle (for  phonograph cartridges) or small automobile 
beverage cooler.  (microphones)

Doug Moore kb9tmy