The selenium rectifier "test"

[Chester Copperpot]

The first time I heard this was about 1980 in a Portland, Oregon TV
repair shop. The technician said something like, "First you get an
empty trash can - then take the selenium rectifier and hold it above
the can and let it go. If it makes a thud noise - it's bad."

Does any one know the origins of this joke or maybe when they first
heard it?

[Peter Wieck]

There are many versions of this. I believe it started with caps. "Not a matter of 'if' it is bad, but 'when' it is bad", and so on.

Selenium rectifiers are reasonably reliable, almost as silicon, more than tube rectifiers. But the consequences of failure are so awful that replacing/bypassing them is just the right thing to do.

Peter Wieck
Melrose Park, PA

[Foxs Mercantile]

Post by Peter Wieck
Selenium rectifiers are reasonably reliable, almost as silicon,
more than tube rectifiers.

Well, no. The problem with selenium rectifiers is they, like tubes,
have an internal resistance. And with age that goes up. Causing more
heat and finally failure.

It is the internal resistance of selenium rectifiers that require an
additional resistor in series with a silicon diode to bring the B+
back down to the original design value.

[John Robertson]

Post by Peter Wieck
There are many versions of this. I believe it started with caps. "Not a matter of 'if' it is bad, but 'when' it is bad", and so on.
Selenium rectifiers are reasonably reliable, almost as silicon, more than tube rectifiers. But the consequences of failure are so awful that replacing/bypassing them is just the right thing to do.
Peter Wieck
Melrose Park, PA

Other than a bad smell, selenium rectifiers fail open, whereas Silicons
short. I prefer the former failure mode, but fuse for the later when
upgrading from Selenium to Silicon.

Fusing for Selenium diode/bridge was typically only on the outputs.

Silicon diodes/bridge need fuses on the AC side to protect the
transformer as well as outputs (when replacing Selenium).

John :-#)#

[o***@gmail.com]

In addition to forward resistance increasing, they also develop reverse leakage, adding to the heat factor.

Bill(oc)

[c***@snyder.on.ca]

Post by o***@gmail.com
In addition to forward resistance increasing, they also develop reverse leakage, adding to the heat factor.
Bill(oc)

Selenium dioxide is the major compound produced when a selenium
rectifier is overheated. It can cause severe burns to the mucous
membranes and severe respiratory tract, skin, and eye irritation. It
is also a dermal sensitizer in that it can promote allergic reactions.
Fortunately it is not consider a carcinogen. Another fortunate thing
is the BAD smell. When I say BAD, I mean really, really, _really_
_BAD_. Our odor threshold for selenium dioxide is 0.0002 mg/m3.

The allowed exposure for selenium and it compounds (expressed as
selenium) is:
0.2 mg/m3 OSHA TWA
0.2 mg/m3 ACGIH TWA
0.2 mg/m3 NIOSH recommended 10 hour TWA
0.1 mg/m3 DFG MAK TWA (total dust);
1 mg/m3 DFG MAK 30 minute peak, average value, once per shift

[John Robertson]

Post by c***@snyder.on.ca

Post by o***@gmail.com
In addition to forward resistance increasing, they also develop reverse leakage, adding to the heat factor.
Bill(oc)

Selenium dioxide is the major compound produced when a selenium
rectifier is overheated. It can cause severe burns to the mucous
membranes and severe respiratory tract, skin, and eye irritation. It
is also a dermal sensitizer in that it can promote allergic reactions.
Fortunately it is not consider a carcinogen. Another fortunate thing
is the BAD smell. When I say BAD, I mean really, really, _really_
_BAD_. Our odor threshold for selenium dioxide is 0.0002 mg/m3.
The allowed exposure for selenium and it compounds (expressed as
0.2 mg/m3 OSHA TWA
0.2 mg/m3 ACGIH TWA
0.2 mg/m3 NIOSH recommended 10 hour TWA
0.1 mg/m3 DFG MAK TWA (total dust);
1 mg/m3 DFG MAK 30 minute peak, average value, once per shift

Well, it is a good thing then that the only Selenium rectifiers I've
been exposed to are in jukeboxes and a few very old Genco pinball games.
These are usually rated at a couple of amps max and so are pretty small
(relatively speaking - sorry Alfred). I wasn't aware as a result of the
potential health hazards.

The rotten egg smell is pretty rare in these machines in my somewhat
limited experience (30 some years fixing the suckers)

John :-#)#

[philo]

Post by o***@gmail.com
In addition to forward resistance increasing, they also develop
reverse leakage, adding to the heat factor.

<snip>


I repaired industrial battery chargers for a living and when I started
in 1975 there were still some selenium rectifier chargers in use. They
were already obsolete but we repaired them by converting to silicon
power diodes.

Most of the chargers had adjustment taps which allowed one to keep
increasing the output as the rectifiers aged.


One thing though...even after the selenium rectifier chargers were
obsolete, the kept producing them for automotive chargers.


The reason they did was because since the leads clipped onto the
batteries it was pretty easy to short them out. The rectifiers had a
high enough internal resistance that a momentary short would not hurt
anything

[Peter Wieck]

Post by John Robertson

Post by Peter Wieck
There are many versions of this. I believe it started with caps. "Not a matter of 'if' it is bad, but 'when' it is bad", and so on.
Selenium rectifiers are reasonably reliable, almost as silicon, more than tube rectifiers. But the consequences of failure are so awful that replacing/bypassing them is just the right thing to do.
Peter Wieck
Melrose Park, PA

Other than a bad smell, selenium rectifiers fail open, whereas Silicons
short. I prefer the former failure mode, but fuse for the later when
upgrading from Selenium to Silicon.
Fusing for Selenium diode/bridge was typically only on the outputs.
Silicon diodes/bridge need fuses on the AC side to protect the
transformer as well as outputs (when replacing Selenium).
John :-#)#
--
(Please post followups or tech inquiries to the newsgroup)
John's Jukes Ltd. 2343 Main St., Vancouver, BC, Canada V5T 3C9
[phone] or Fax [phone] (Pinballs, Jukes, Video Games)
www.flippers.com
"Old pinballers never die, they just flip out."

That would be about half my point - failure modes. The other half is my direct experience with both materials. Some of you may be aware that I am overly fond of 1970s vintage AR and Dynaco electronics. So, let's use 40 years old as a generic age-range. 100% of the AR and Dynaco items (AR amp, Model R receiver and Tuner) have one or more failed SILICON diodes in the power-supply. So, about a 30% failure rate. With Dynaco, that goes to about 50% (ST120/ST80/SCA80 and so forth). Thankfully most of them do not use blocks but individual diodes.

That is about the same as the failure rate I see in selenium diodes in say... Zenith radios, ST-70 amps and the typical Transoceanic. Which leads me to conclude that in actual practice, they are about the same in survival rates/times. I still replace them out-of-hand, as I do with similar vintage silicon diodes.

Peter Wieck
Melrose Park, PA

[Jay Hennigan]

Post by Chester Copperpot
The first time I heard this was about 1980 in a Portland, Oregon TV
repair shop. The technician said something like, "First you get an
empty trash can - then take the selenium rectifier and hold it above
the can and let it go. If it makes a thud noise - it's bad."
Does any one know the origins of this joke or maybe when they first
heard it?

No, but about the same time some friends and I made a "fuse tester". It
consisted of a power cord, a N/O pushbutton, a fuseholder and a lamp.
The pushbutton was in series with the line and the fuseholder and lamp
in parallel.

Instructions were "Insert fuse, push button. If lamp lights, fuse is bad."

[J.B. Wood]

Post by Chester Copperpot
The first time I heard this was about 1980 in a Portland, Oregon TV
repair shop. The technician said something like, "First you get an
empty trash can - then take the selenium rectifier and hold it above
the can and let it go. If it makes a thud noise - it's bad."
Does any one know the origins of this joke or maybe when they first
heard it?

Hello, and while I can't comment on the joke, according to Dr. Raymond
Stantz selenium acts as a magnet for paranormal phenomena. So be sure
to include your ghost detection equipment when testing the rectifier.
Sincerely,

[o***@gmail.com]

Sounds like Arsenic and Old Seleniums.:-)
Phil Nelson, a really cool dude who used to post here, has a website that was featured in a murder mystery involving a selenium rectifier..

http://antiqueradio.org/tvshow.htm

Bill(oc)

[John Robertson]

Post by o***@gmail.com
Sounds like Arsenic and Old Seleniums.:-)
Phil Nelson, a really cool dude who used to post here, has a website that was featured in a murder mystery involving a selenium rectifier..
http://antiqueradio.org/tvshow.htm
Bill(oc)

Great write up!

And you can watch the movie on youtube!

John :-#)#