On Sunday, 2 December 2018 06:30:51 UTC, wrote:
How do you test a Selenium Rectifier?

Yes, I am aware that they should be replaced, but on preliminary tests
of this 1956 Zenith tube AM-FM Radio, I want to know if it's working. My
digital multimeter shows 1meg in one direction, 2.5 meg the other way.
NOT DISCONNECTED FROM THE CIRCUIT. To me, that seems bad, but I have not
worked with one of these in many years, and never had to replace one in
the old days. My meter was climbing, probably from the filter caps.
during this test.

Selenium stacks have high Vf & high reverse leakage. DMMs don't apply enough voltage. Probably the simplest way to test is to power it up. They fail by Vf increasing, causing overheating & lots of toxic selenium fumes, so best not tested indoors.

Replacement is probably a wise option. But add a resistor & fuse, seleniums act as current limits. There are lots of old scopes still running with selenium EHT rectifiers in them.


NT