[ARC5] Selenium rectifiers

[millerke6f at aol.com]

A cautionary note:
Back in the spring of 1959 I finished my Army National Guard active duty training and returned to my home in Eureka to find that one of the Guard Members had a job waiting for me in a local Radio and TV store. Wow!  17 years old and I had a real job.  I was assigned to the Radio and Record player bench and did some outside TV tube jockey work (didn't have a clue on TV repair... but managed to survive and was a quick learner).  I apologize for the long introduction, but had to set the period.  
One of the first radios to come across my bench was a Zenith Trans Oceananic  with low B+.  Well that problem suggested that I just wire a NEW Silicon Diode across the Selenium rectifier and SHAZAM the radio came to life for a few seconds and then went silent.  Now many of you folks know the problem with that simple fix.  The head technician also knew the causal agent (namely my dumb solution).  The filament string in the radio was also powered from the DC provided by the Selenium rectifier scheme and the greatly improved rectifier efficiency applied toooo much voltage to the tube filament string and fortunately one of the little tubes became to fuse.  
The moral of this story is don't just stick a silicon diode in place of a Selenium without looking at the load.
Bob, KE6F


-----Original Message-----
From: Kenneth G. Gordon <kgordon2006 at frontier.com>
To: arc5 at mailman.qth.net
Sent: Sat, Mar 12, 2022 3:18 pm
Subject: Re: [ARC5] Selenium rectifiers

On 12 Mar 2022 at 15:38, Jack Antonio wrote:

> But yeah, I do treat seleniums with suspicion.

Well, everyone here can, of course, do what they wish with regard to selenium rectifiers, but I 
won't have them in the shack if I can avoid it.

Most will deteriorate over a long period of time, some even while being stored. They become, 
essentially, resistors, not rectifiers.

Then, if they short out under load, they spit out a gas that is poisonous, besides stinking to 
high heaven.

IMHO, it is far less hassle to simply replace them with silicon. than to continue to worry about 
them...and I am NOT in favor of shot-gun replacing any other component without testing it 
first.

I can't and won't trust the darned things.

In the unit in question, we were told that the selenium rectifiers in this rotary converter are in 
the voltage-regulation part of that unit. By the very fact that those are in that part of the circuit, 
I would be replacing them even if they "test" good....for now.

Although I am not "intimately" knowledgeable of that particular circuit, it seems to me that if 
they control the voltage regulation of the unit, it would be far better to replace them, now, with 
silicon rather than depend on such an iffy component.

It also seems to me that if that voltage-regulator was not completely up to specifications, that 
COULD be the reason for the unusually high current the unit exhibits at no load. If there was 
more AC on the output of the selenium rectifiers than there should be, for instance.

Of course, you MAY have to consider and account for the differing voltage-drops of selenium 
vs silicon, but in most cases that won't matter.

But since it is your equipment, you can do as you want.

Ken W7EKB
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