[Elecraft] More than you may want to know about crystals

[Ron D'Eau Claire]

Nice summary, James.

In this application, the impact of changing the resonant frequency or
motional inductance of the crystal by overheating it or allowing air
into the "can" will show up in degraded filter performance. How much and
when it will occur is uncertain. It's not just a matter of the crystal
not working at all or an oscillator obviously being off frequency.

I've built a number of "ladder filters" like the K2 uses using various
surplus rocks. My usual method of mounting them is to have a "ground
plane" of copper on the top of the board, to which the can is soldered
to the copper at a couple of spots. The leads go through holes to traces
on the bottom. I've almost always gotten away with it. ALMOST always
<G>. Can't say whether it was a marginal crystal that changed or not.
But most of those were older-style and larger sealed cans too. The HC6/U
variety. Newer crystals are much smaller and, I suspect, much more
sensitive to overheating. 

Ron AC7AC
K2 # 1289