B. W. Salt. ) writes:
In article , B Stanton
(ll.com) wrote:

There are also rectifiers that look like multiple square
pieces of metal separated by some rectifying material.

Those are selenium rectifiers. No longer used except as replacements in
very old equipment. Smell like rotten eggs when they fail. I still have a
battery charger that uses selenium...

I don't think anyone uses them. The standard routine when they need
replacing (or for that matter you just want them out of the house) is
to use a silicon power diode with a series resistor to compensate
for the differences.

Getting replacement parts is not the issue here, people just don't
want to put selenium rectifiers back in a piece of equipment.

Michael