N Cook wrote:

snip

Let this be a lesson to anyone in the UK -
DO NOT store Rochelle crystal cartridges in lofts or sheds.
The crystal must be hygroscopic.

snip

Anyone reckon I can rob the crystal from a piezo ceramic pickup to fudge a
functional and "as original" repair?
I assume piezo-ceramic is not prone to this problem over 40 years.

FWIW, I have seen a number of grow-your-own Rochelle salt crystal
experiments on the web; the process seems rather straightforward and
the results look good if the work is performed with care. If you
were successful with this cartridge and posted your work I'm sure
it would attract a lot of attention :-)

Regards,

Michael