Life span of selenium rectifiers?

[Jeffhs]

I have two Zenith radios, K731 and C845, both with selenium rectifiers in their power supplies. Both radios still sound great, no hum or other problems as yet. However, I'm wondering how long the selenium rectifiers in these sets are going to last. The one in my C845 is as old as the radio (50 years this year); the '731's is also the radio's age (47 years). Are these rectifiers on their last legs and bound to fail literally any day now, or will they go five, ten more years? Aside from the usual symptom of shorted seleniums (when the part emits a toxic gas that smells of rotten eggs), are there any other signs (such as decreased sensitivity, distortion of the sound, etc.) that the rectifier is about to fail?

BTW, what is the world's record (if there is one) for longevity of seleniums? Are the ones in my radios close to setting, tying or breaking that record?

Kind regards,

[AUdubon5425]

I have a Warwick-built Silvertone made in 1955 or '56 that's on its original selenium. I have read concerns about them a while back, and I too am interested if they give any signs of imminent failure.

[jr_tech]

I have several late 40s portable radios that work fine with their original selenium rectifiers. When I restore one of these sets, I usually just check the voltage output of the rectifier, and if it is up to spec, I leave it alone.

Some that needed to be replaced may have been damaged by failure of a part downstream, such as a filter cap short.

These radios are not "daily drivers" however, but I would like for them to work if I turn them on for a demo.

If you use those Zeniths a lot, it might be a good idea to replace the selenium rectifier... it could fail tomorrow, or in 50 years! No way to really predict. Mushy, weak audio could be a clue that the rectifier output is dropping...measure that B+ voltage!... As the output drops, the rectifier will run hotter, and heat will accelerate failure!

jr

[radiotvnut]

The ones I've dealt with usually simply work fine one minute and burn up the next.

I've seen others that exhibited low or no B+ on their output.

I've been told, by the old repairmen that I've talked to, that some of these devices failed after only a few years. Then, there are those, like what's in your radios, that go on for 50 years without trouble. How long will they continue to last? Who knows. Maybe 5 minutes, maybe 5 months, maybe 5 years, maybe even another 50 years.

I usually replace them with a modern silicon diode and a resistor, even if the old part is still good.

[compucat]

I had a Zenith radio that used a selenium rectifier a few years back and when I got it, the B+ was about half what it should be so I replaced it. I presently have a 1957 RCA 8" TV and a late '50s Zenith bakelite radio that are both on their original seleniums with no problems. It it worries you, then change it. If not leave it until it fails.

[Zenith26kc20]

My Zenith H500 Transoceanic started to lose the upper frequencies. I checked and B+ was a bit down. The selenium was weak. It was about 40 years old at the time. I recommend carefully matching the voltage on the schematic to the radio/tv for protection of electrolytics. My TS-14 Motorola developed the "jitters" after I replaced the seleniums with silicon diodes. The B+ was around 45 volts too high acording to the schematic. I wasted a LOT of time checking the rest of the set until I ran the set on a variac and lowered the voltage and it started to behave. I put a 10 ohm 5 watt in series with each selenium to allow proper line voltage.
Since it had new electrolytics, they didn't get warm like some originals will while they reform.

[Phil Nelson]

I treat them like electrolytic and paper capacitors, which can also fail without warning. A 1N4007 diode costs less than $1. Unless the radio is a shelf queen, I can't think of a sensible reason not to replace the selenium. You can disconnect the old rectifier and leave it in place, if you care about appearance.

Phil Nelson

[AUdubon5425]

Thanks for the advice folks - I have at least three radios I regularly use running on seleniums.

[Sandy G]

I have an EH Scott 800B that the selenium went south on...Liked to have NEVER got the Stink outta the house !

[leadlike]

I just worked on a radio with a neat issue: it had bad filter hum, so I did a complete recap. It STILL had filter hum, B+ was dead on. I was pretty frustrated by this persistent hum, but I pressed forward and replaced the selenium with a diode and resistor. B+ was still the same and the hum was gone. It's just another 50+ year old part that can cause weird problems.

[jr_tech]

Originally Posted by Sandy G

I have an EH Scott 800B that the selenium went south on...Liked to have NEVER got the Stink outta the house !

Anybody know how toxic the gas emitted when a selenium fails is? Should this be a major concern?

jr

[Sandy G]

Prolly isn't any good for you, but I doubt if you'd stay around in toxic levels long enuff to do any damage, since it stinks SO bad...Sulphurous, rotten egg, just NASTY smell !

[Kiwick]

I once had a selenium rectifier go dead short and take out the power transformer in a matter of seconds, luckily, it was a crappy beat up plastic radio.
I'm always replacing them with silicon parts after that.

The only ones i'm willing to leave alone are the full wave seleniun bridges used in my Lesa tape recorders, because they were oversized and ran cool, and also because there's a fuse to protect the transformer in case they short.