PDP 11 gear finally moved

tony duell ard at p850ug1.demon.co.uk
Tue Jul 21 04:52:50 CDT 2015

> > But yes, selenium rectifiers rarely work now (although there are exceptions)
> > and when they fail they can take out the mains transformer. And they smell
> > horrible (think of school dinner cabbage!)
> Huh? All devices with selenium rectifiers that I/we own are OK. And a
> selenium rectifier only fails if overloaded. See for example the power
> supply of the LGP-30:

I've had many more selenium rectifiers fail than electrolytics. But actually yes, I 
do still have some original selenium rectifiers in operation. 

Come to think of it, every UK Telephone 706, 746, 722, 776, etc (The common 
1970's telephones) had a selenium rectifier stack ( 8 diodes) as part of the
voltage regulator circuit. I have never heard of one of those failing.

> And all my radio/TV sets with selenium rectifiers are OK, too. I had to
> replace one in my TV as it had a too high resistance, but only because I
> didn't know at that time that I could re-fasten the nuts of the rectifier
> (selenium rectifier plates can suffer from contact resistances).

The ones I mainly have are those flat 'contact cooled' ones that you bolt onto
the chassis. You can take those apart and bend contacts, etc, but most of the time
I replace them with a suitable silicon device.


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