Calling the veterans - what is this?

[factory]

I've never been able to swap out selenium rectifiers with silicon ones and not have hassles. Because of the much lower forward voltage drop and lower on resistance, and lack of reverse voltage protection that silicon parts have in comparison.

OP I would expect the drive to experience much higher stress due to the current-limiting and voltage-limiting the old diodes provided. It depends on the motor's load but you might want to add series resistance and MOV's to protect the windings and drive from back EMF. You'll get much more torque and speed- if the drive doesn't croak.
For a replacement, I would put in an oversized 25A 1,000PIV bridge rectifier module (a few dollars) like GBJ2510 or GBPC2510 has crimp terminals which might be easier to deal with.
edit: there's 6 diode stacks? Then you need individual diodes like 6A10's 6A 1,000PIV each. I'm not sure how the motor is wired up.

Even today there are customers specifying selenium rectifiers for use in cathodic protection systems, they find they are tougher when it comes to lightning. The diodes act like a huge MOV is built-in there. There is some fungus that attacks selenium diodes causing their downfall, and selenium smoke is highly toxic.

Still made over here too, some data on both webpages below on the "please click here" links,
https://www.gdrectifiers.co.uk/products/category/power_assemblies/selenium_suppressors/
https://www.gdrectifiers.co.uk/products/category/power_assemblies/selenium_rectifiers/

Modern silicon replacements can fail more often, maintenance had this with a crane part at work, the design of the assembly they bought into the lab suggested it had a Selenium stack, in a previous life.
The solution these days, now maintenance has been outsourced to external contractors, seems to be just replace the entire lot, including the motors & hoist. 

David

[jdragoset]

FTR Replacement Guide on eBay
https://www.ebay.com/itm/303441589656?hash=item46a6873598:g:pXIAAOSwQj9eGgwD

Universal Rectifiers still builds them and also use them for AC and DC surge arrestors.
https://www.universalrectifiers.com

[CaptDon]

We had a 100 amp continuous duty battery charger that had a huge full wave selenium rectifier in it. I remember hooking it to a locomotive (64vdc resting, engine off) and when switching on the A.C. power the rectifier blew and the locomotive continued to backfeed it!!! WOW!!!! BANG BOOM CRACK CRACK like a pistol!!! It didn't quit burning and smoking until unhooked from the locomotive!!!! SMELL.....HOLY CRAP and then some!!!
These things are still in operation in railroad shops!!! They are still in operation in the signalling systems on some short line railroads, mostly as battery chargers because when mains are lost the batteries may go 100% dead and the series resistance of the selenium rectifiers limits the charge current into a nearly dead battery.

[vidarr]

It is a battery isolator.

[med6753]

When silicon rectifiers become more readily available and cheaper Tektronix offered update kits for the scopes that had selenium rectifiers in their PSU's. The kit included the rectifiers as well as appropriate dropping resistors to insure correct voltages.   

[DavidAlfa]

A proper replacement would be a power zener+normal diode, in series.
Enjoy your stove

[alm]

FTR Replacement Guide on eBay
https://www.ebay.com/itm/303441589656?hash=item46a6873598:g:pXIAAOSwQj9eGgwD

Reading the table of contents, it seems to be a cross reference of other manufacturers selenium rectifiers to Federal selenium rectifiers, not how to replace selenium rectifiers with silicon rectifiers.

[factory]

A proper replacement would be a power zener+normal diode, in series.
Enjoy your stove

It was for a 1/4HP 115V DC motor, the start up surge current would EOL the Zener very quickly, unless a series resistor was added.

David

[Chris56000]

Hi!

In the UK selenium metal rectifiers were used as the mains h.t. rectifier in a.c./d.c. television receivers  for many years, and it was far from unknown for these things to stink the living room out for months without showing any more obvious signs of failure, and the UK's R.S.P.C.A. regularly had to deal with animal cruelty and neglect cases because owners that had pets as well as the TV never twigged that the TV was the cause of the nauseating stink, because the dud rectifier didn't drop the h.t. enough to make the fault obvious!

The R.S.P.C.A. were equally as baffled when the silicon diode rectifier came into use  for TV set h.t. supplies from about 1961/1962, that caused a sudden massive reduction in these neglect/cruelty cases all in one go at the same time!

I dealt with many pieces of thermionic valve gear using these rectifiers (and dont forget many of the earlier solid–state radiograms & record–players released by UK makers had selenium diode l.t. rectifiers as well!), but I have to admit I never had to deal with an abominably stinky one – they just went high–resistance causing very low h.t. or l.t. output!

Chris Williams

[CatalinaWOW]

Here is a pretty good description of how they work in general.

[m3vuv]

its an electricity operated smoke/stink bombe.