Selenium Rectifier M100B

Hello everyone.

I am working on the Wired Selection receiver (WSR5-L6) on the M100B. My question is in regards to the selenium rectifier in the unit. The one that is in place seems fine and I usually do not replace them in newer units, but this one is 63 years old. Just looking for some advice. I know that a new bridge must be fused, if I go that route. Well, if anyone has delt with this before, please help me out.

Thanks, Mark

Selenium rectifiers are old technology, and prone to failure.
Of course you'll hear a ton of people argue about replacing them.
So lets not go there.

I'd prefer to have peace of mind - and replace with silicon diodes. (much more reliable)
At times, certain modifications have to be implimented - to keep the rectified voltages in spec, since silicon doesn't suffer from the voltage drop/sag like selenium does.
Series resistance - calculated depending on each application.

Hi Mark,
In this case, in the WSR's, I tend not to replace it, as long as it has over 16 v output. Should it fail, there is no consequence (ES "keys" will "stick down"), other then the "smell"--I'm told--I have no sense of smell--my advantage- HERE-only !! . If replaced it MUST be fused (1 ASB) on the AC side, as that transformer will not live thru a "short".
Ron Rich

Cougar Electronics manufactures brand new selenium rectifiers:

http://www.cougarelectronics.com/selenium.htm

Mark, it depends on the machine type and where-how it will be used.

When I rebuilt old jukes for retro locations I always replaced the rectifier. The main goal is reliability.
In the case of Seeburgs using the Tormat system there is the added use of the low-DC for bias on the trip thyratron. If the rect fails or "goes low" the trip tube will fire continuously. It one is lucky the tube will wear out before it destroys the trip coil and possibly causes it to short to chassis thus killing the main transformer (fuse the 150vac line).

On the older E-M machines such as yours the only real danger from a failed rect might be if a stepper tube is used and bias failure caused it to cook a stepper magnet. this can easily be prevented by using a 1/2 watt 100 ohm resistor in place of the larger one-watt. The half watt will act as a slo-blo fuse and burn up if left energized.

In machines where DC motors are used, these often become sluggish with glazed bearings and the added 12-15% boost in voltage a silicon rect gives over a selenium may improve mech performance a bit.

Aside from a very unpleasant odor that might occur if the selenium rect fails, there isn't an overriding need to replace it in your case.

Rob/NYC