Grounding crystal cases
 

Anyone have an opinion on whether or not crystal cases (e.g., HC49, HC45,
etc.) ought to be grounded or not? I've done some Googling, and I've found
various cases where people recommend it (albeit without much explanation as to
what they think will change when they do it) and no cases where it was
specifically not recommended.

Thanks,
---Joel

Grounding crystal cases
 

Most of the time when I've seen crystal cases grounded it has been in
crystal filters, where it is supposed to help with feedthru.

...

"Joel Kolstad" wrote in message
...
Anyone have an opinion on whether or not crystal cases (e.g., HC49, HC45,
etc.) ought to be grounded or not? I've done some Googling, and I've
found various cases where people recommend it (albeit without much
explanation as to what they think will change when they do it) and no
cases where it was specifically not recommended.

Thanks,
---Joel

Grounding crystal cases
 

"Joel Kolstad" ) writes:
Anyone have an opinion on whether or not crystal cases (e.g., HC49, HC45,
etc.) ought to be grounded or not? I've done some Googling, and I've found
various cases where people recommend it (albeit without much explanation as to
what they think will change when they do it) and no cases where it was
specifically not recommended.

I don't know. FT-243 crystal sockets had no means of grounding the crystal
case, which likely wouldn't have mattered since except for the metal access
side, they were bakelite. But it was pretty common to see a grounding
"spring" on HC6 crystal holders, at least those had metal cases. ANd it
seems more common to see metal cased crystals on circuit boards grounded
than not grounded.

Now, perhaps those springs on the old HC6 sockets were there more to
hold the crystal in place. But I always assumed that by grounding them
you'd stabilize the capacitance of the case to the rest of the crystal.
If you just leave the case ungrounded, then external things can affect
that capacitance.

Obviously the case affects the tuning of the crystal. I remember one
guy writing in CQ forty years ago where he'd open up HC6 crystals so he
could grind them on frequency, and he made the point that he couldn't
measure the new frequency accurately unless the case was back on at least
partially. Given that, if you ground the case you put things at a known
level.

If nothing else, grounding the case adds mechanical stability. WIth that
in mind, is there some reason you can come up with why you shouldn't ground
the case (trying to figure that out might help to figure out whether
they should be grounded).

Michael VE2BVW

Grounding crystal cases
 

Joel Kolstad wrote:
Anyone have an opinion on whether or not crystal cases (e.g., HC49, HC45,
etc.) ought to be grounded or not? I've done some Googling, and I've found
various cases where people recommend it (albeit without much explanation as to
what they think will change when they do it) and no cases where it was
specifically not recommended.

For most solid-state oscillators it makes sense to ground.

For tube oscillators where the two pins to the crystal could be at high
potential, it is probably better to not ground. In some Pierce or
Modified Pierce oscillators you find either plate or screen potential;
nominally this is supposed to be blocked by a ceramic capacitor (e.g.
0.001uF) in most designs but you'd be surprised how often this was left
out!

Tim.