Seleniums don't necessarily age just sitting around, unless the ambient
temperature and humidity are high.  I have several NOS examples that meet
and usually exceed spec.
I used to think these things were a pariah, and replaced them with silicon
diodes whenever I ran across them. Gradually, over the years I have found
many applications where they are still cooking along, doing their job.
Beware the "must replace all (fill in the blank) pox.  Especially with
historically significant artifacts.
There are still generator regulators and generator control units flying
around on old aircraft that contain seleniums, many of which are OEM from
the 40s and fifties.
I'm not saying they shouldn't be upgraded, but in circuits where they are
not run near their current ratings, they often last for multiple decades. 

Scott W7SVJ

-----Original Message-----
From: [email protected] <[email protected]> On Behalf
Of Kenneth G. Gordon
Sent: Saturday, March 12, 2022 12:55 AM
To: 'Charles' <[email protected]>; Robert Downs
<[email protected]>
Cc: [email protected]
Subject: Re: [ARC5] No-load current of dynamotors?

On 12 Mar 2022 at 1:49, Robert Downs via ARC5 wrote:

> That isn't too bad given that the front to back ratios of the
> Seleniums is probably down to next to zilch.  Equates to roughly 35%
efficiency.
>
> However, unless the selenium plates were actually made in the last 20
> odd years or less (very unlikely), you were damn lucky that the whole
> machine didn't go up in a cloud of smoke.

Yes!!!!

> I would not light it off again until you have replaced the Selenium
> rectifiers with Silicon and equivalent heat sinks.

Abso-freakin-lootely!!!!!!!!!!!

Gee....

Ken W7EKB
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