Selenium Rectifier Question

[Rich12]

I'm restoring a 1949 Emerson TV that has had some prior work done. As you can see from the pics 4 silicon diodes have been wired in. I can only pick up writing on one it appears to be an R170 which I believe is 2.5 amps / 1,000 volts. The soldering joints and connections look very well done. My concern is that they appear to connect in circuit with the existing 2 rectifiers instead of being detached? Also there is no additional resistor on the lines to the electrolytic's. I don't want to break it if doesn't need to be fixed? I'm a long way from putting this on a viac, I still need to replace numerous paper caps, electrolytic's and at least a couple tubes. Comments and suggestions are appreciated. Thanks!

[Eric H]

I just read somewhere that it's perfectly acceptable to just place the diode across the Selenium rectifier, leaving it in the circuit, this is because Seleniums never short, they just go up in resistance until they fail.
As for adding resistance you'll need to get it running and check the B+ against the spec and adjust accordingly.

[Rich12]

Thanks Eric!

[jr_tech]

Although some might consider it to be a "sloppy practice", I usually just bridge the seleniums with the diode... the original appearance is preserved and I have never had a problem.

jr

[reichsrundfu]

Do so at your own peril! Suggest you disconnect one side of each original selinium. Ask me how I know this...... It was not a pretty event.

George

[jr_tech]

Originally Posted by reichsrundfu

Do so at your own peril! Suggest you disconnect one side of each original selinium. Ask me how I know this...... It was not a pretty event.

George

OK, I'll play... how do you know this?

Inquiring minds would love to hear "the rest of the story"

jr

[wa2ise]

The selenium would see the peak inverse voltage, and after a while it may not take it any longer, and then start to conduct and then fail...

[rca2000]

Originally Posted by reichsrundfu

Do so at your own peril! Suggest you disconnect one side of each original selinium. Ask me how I know this...... It was not a pretty event.

George

Been there...DONE that...many years back. i had a Motorola tv, 12LP4 tube..I was only 15 at the time...and still learning. Someone had ALREADY bridges the seleniums with diodes. but one of them STILL was smoking and smelling. So...I lifted the diode from one leg of the sel..and all was ok..

[broadcaster]

I always always lift one end of seleniums.

[Rich12]

thanks everyone, I'm going to go the safe route and disconnect a side from each. I really appreciate all the input on this!

[init4fun]

Originally Posted by jr_tech

Although some might consider it to be a "sloppy practice", I usually just bridge the seleniums with the diode

So I guess ya can call me "Mr. Some" , cause I always fully disconnect them , leave them in place , and then run the wires to a terminal strip holding the diodes (and if used , the dropping resistor) Many times , the same screw that holds the selenium in can be used to piggy back the terminal strip right there .

Originally Posted by wa2ise

The selenium would see the peak inverse voltage, and after a while it may not take it any longer, and then start to conduct and then fail...

Exactly

[old_coot88]

Bridging a selenium with a Si diode does not mitigate the effect of reverse leakage in the selenium. Heating due to reverse leakage increasing is part of the failure mode (in addition to heating due to increased forward resistance). Always take the selenium out of circuit.

[jr_tech]

Originally Posted by old_coot88

Bridging a selenium with a Si diode does not mitigate the effect of reverse leakage in the selenium. Heating due to reverse leakage increasing is part of the failure mode (in addition to heating due to increased forward resistance). Always take the selenium out of circuit.

Originally Posted by wa2ise

The selenium would see the peak inverse voltage, and after a while it may not take it any longer, and then start to conduct and then fail...

A compelling reason that I had not considered... thanks guys!

jr

[timmy]

Other then that they smell bad when they go sour.

[Eric H]

I've only replaced the Seleniums in a few sets, most of the time they still work satisfactorily.
I know there's a risk of a stinky failure but as often as they get used it's pretty low.