Life span of selenium rectifiers? - Videokarma.org TV - Video

Jeffhs · #1 08-03-2009, 12:08 PM

I have two Zenith radios (K731, C845) with selenium rectifier stacks in the power supply. How long are these rectifiers supposed to last before they fail? My sets were made in the '60s and are still working. Oddly, however, my MJ1035, which was also manufactured in the mid-sixties, has a silicon diode as a low-voltage rectifier. When did Zenith make the switch from seleniums to silicons? Hmmm.

Thanks in advance.

spkrman57 · #2 08-03-2009, 01:05 PM

I would replace at your earliest convenience if you plan on keeping the unit for the long term.

Just my opinion though. I know these sometimes last longer than they were meant to, but sometimes you can avoid catastrophic damage by replacing them before they go bad.

Regards, Ron

radiotvnut · #3 08-03-2009, 05:22 PM

They are like most other electronic parts. They might last a few years or a few decades. When they fail, your nose will know it!

For the most part, I think Zenith (as well as most others) went to silicon by the mid '60's. I do have a cheap low end Zenith table AM/FM radio from '67 that had a selenium rectifier. The chassis is an older design; but, the tubes have '67 date codes.

Andyman · #4 08-03-2009, 05:45 PM

From the little bit I've read about them, especially in Dynaco PAS mods, they are one of the first things folks are advised to replace. Apparently a simple diode can do the job, but I'm not knowledgeable on how to select a replacement.

ChiefRider · #5 08-03-2009, 09:35 PM

Quote:

Originally Posted by Andyman

From the little bit I've read about them, especially in Dynaco PAS mods, they are one of the first things folks are advised to replace. Apparently a simple diode can do the job, but I'm not knowledgeable on how to select a replacement.

Same here. I also have a Zenith 731 that works, but I would like to replace the original rectifier. How do I select a replacement. Sorry for the dumb question- I can solder, but that's about it!

Chief

radiotvnut · #6 08-03-2009, 09:46 PM

A 1N4007 diode will work. Also, it would be a good idea to stick a 5 watt power resistor with a resistance between 22 and 68 ohms ahead of the diode. The reason is because a selenium diode has more voltage drop than a modern silicon diode.

Reece · #7 08-04-2009, 09:48 AM

And remember when replacing a selenium with a silicon diode, the band end of the diode, the cathode, goes towards the B+ in the radio, i.e., towards the part of the circuit with the electrolytic filter caps.

I have a Zenith AM/FM ca. 1960 with a selenium rectifier, the selenium was already fried when I got it, and it took out a resistor and melted a wire.

On the old selenium, which was painted blue, I put my ohm meter probe on one end and started at that end touching plate by plate with the other probe, got readings. About half way across, where the blue paint had turned black, no more readings.

Replaced the selenium and resistor, recapped it, and it plays like a champ. Best to get 'em outa there.

Reece

Jeffhs · #8 08-04-2009, 09:48 AM

I appreciate all the advice, but I'm not sure I want to try to replace parts under the chassis; I've only replaced a chassis component once in any of the old radios I've owned, and that was some 25 years ago or more. Besides, I don't know where I would get a 1N4007 diode, as the only Radio Shack store near here closed a few months ago and I don't know if there are others in this area. I think there is still a RS store about 20 miles from here, but since I don't drive, I don't know how I would get to it.

MelodyMaster · #9 08-04-2009, 10:03 AM

Quote:

Originally Posted by Jeffhs

I appreciate all the advice, but I'm not sure I want to try to replace parts under the chassis; I've only replaced a chassis component once in any of the old radios I've owned, and that was some 25 years ago or more. Besides, I don't know where I would get a 1N4007 diode, as the only Radio Shack store near here closed a few months ago and I don't know if there are others in this area. I think there is still a RS store about 20 miles from here, but since I don't drive, I don't know how I would get to it.

Well you asked about how to take care of the radios. Replacing components comes with the territory. I personally have found selenium rectifiers to be pretty reliable, only one failure among many older units. Plus I'm fortunate to have a small crate load of NOS Seleniums if I want to do original parts replacements. But in general, for peace of mind, you should replace it with a Diode and resistor.

The 1N4007 is an extraordinarily common diode, look up on Google for an electronic components parts sales outlet near you, or order online.

toxcrusadr · #10 08-04-2009, 01:15 PM

Melody, I've just been sorting a truckload of vintage parts and have a double handful of very new looking seleniums, which were headed to the scrap metal. FYI.

Jeff, those diodes are so small and cheap, someone around here would probably stick one in an envelope for you if you were serious about doing it.

What happens to all your radios when they quit? Mine never keep working for too long, they always need repair. I got more busted ones than working ones, fur sure.

Jeffhs · #11 08-04-2009, 02:23 PM

Quote:

Originally Posted by MelodyMaster

Well you asked about how to take care of the radios. Replacing components comes with the territory. I personally have found selenium rectifiers to be pretty reliable, only one failure among many older units. Plus I'm fortunate to have a small crate load of NOS Seleniums if I want to do original parts replacements. But in general, for peace of mind, you should replace it with a Diode and resistor.

The 1N4007 is an extraordinarily common diode, look up on Google for an electronic components parts sales outlet near you, or order online.

I said what I said in my post for a reason. I cannot work on radios much anymore because I live in an apartment; it is for this reason that my Zenith MJ1035 sits in my bedroom, unusable because of a bad volume control, and why I really cannot do anything much about replacing components in it or in my other sets.

I understand what you are saying and I realize what's involved in replacing a selenium rectifier with a 1N4007 silicon diode and a dropping resistor, but again, my circumstances do not allow me to do much if any electronic service work anymore. It's been like that for me since I moved here nine years ago. You probably do not live in an apartment building; if you did, you would understand my situation.

You mention "look up on Google" for an electronics parts store near here; what keywords would I use? Second, as I mentioned in my post, there are no stores really "near" where I live--not anymore, anyway. There used to be a Radio Shack in the next town south of here, as I also mentioned, but it is closed and has been for months. (Radio Shack also does not stock much anymore as far as small electronic components are concerned, anyway; their focus over the last few years has been almost exclusively on home theater, high-definition television and computers.) I do not really know where the next nearest RS store is, as I am still not that familiar with this area--even after nine years (I don't get out that much because of an injury I sustained some five years ago that has left me afraid to walk anywhere for fear of getting hurt again, and I don't drive, so that limits me quite a bit as well).

toxcrusadr · #12 08-04-2009, 02:34 PM

Near Lake Erie I see...if you're near Cleveland or Akron there are some radio repair shops that would probably take care of your radios for a decent price. You're in the middle of Radio Land over there.

Jeffhs · #13 08-04-2009, 08:34 PM

Quote:

Originally Posted by toxcrusadr

Near Lake Erie I see...if you're near Cleveland or Akron there are some radio repair shops that would probably take care of your radios for a decent price. You're in the middle of Radio Land over there.

I'm not "in the middle" of anything where I live. The so-called "radio land" you mention is 40-odd miles southwest of me in an area composed, in part, of the Cleveland suburbs of Parma and Seven Hills; it is where all the TV and AM/FM radio towers serving northeastern Ohio are located. My analog TV reception here was so bad without cable I might as well be 140 miles away; digital, forget it, as I would probably get only one station well enough to watch, the same as analog was.

I am really nowhere near Cleveland (where I live is a small town 35 miles east of downtown), and even further from Akron. Moreover, I do not drive and don't know anyone here, so how would I get my radios to any repair shop if there are any such places that will still even look at vintage electronics? (There is a ham radio operator on the next street over from here, but he must have some sort of ax to grind where I'm concerned as he will not have anything to do with me--and I did not do or say anything to turn him against me.) The only TV repair place near here is five miles away or so in the next town, and they wouldn't touch vintage or antique electronics with a ten-foot oscilloscope probe. I know this for a fact because about five years ago, I asked them to look at my 1951 Zenith H511Y radio. They refused. These people won't even look at anything that old, even if I brought it in personally.

If they won't so much as look at (let alone repair) a 58-year-old radio, I honestly doubt very much that they would have anything to do with any of my other vintage radios, all of which, except a 1980-vintage Zenith 13-transistor portable and a Zenith solid-state clock radio of the same vintage, were made over 40 years ago. Most technicians working in what few TV shops there are nowadays know very little if anything about repair of tube-type electronics, having been schooled in solid-state repair techniques. I am reminded of a cartoon I saw years ago in an old issue of an electronics magazine, in which two TV technicians were looking at a 30-year-old TV set with vacuum tubes. Neither technician could figure out what those glowing things on the chassis actually were, so one of them, in disgust, asked the other, point blank: "What the hell is a vacuum tube?"

This may be how many modern TV technicians (AK members such as Doug, drh4683 in Chicago excepted, of course) actually see tube-powered TVs nowadays. Never having seen a vacuum tube in their lives, the sight of these glowing things throws them for the devil of a loop more often than not; in other words, they wouldn't know the first thing about repairing radios or televisions using them.

toxcrusadr · #14 08-04-2009, 08:53 PM

Just trying to help but it sounds impossible I guess.

wa2ise · #15 08-04-2009, 10:59 PM

I used a bridge rectifier salvaged from an old PC power supply. This will allow the filter caps to be recharged twice every cycle of 60Hz powerline, instead of just once. And tube heaters have less hum leakage when they are at a positive voltage compared to the cathodes, like 50V. And this bridge circuit will make the middle of the heater string look to have such a positive voltage, so I rewired the string so the first audio driver tube sees the least AC ripple and a fairly constant voltage as seen by the heater and cathode voltage difference. But the chassis is hot no matter which way the radio's power plug is connected to the powerline. But this is for advanced hobbyists.

In any event, one can acquire a far amount of usable parts from salvaging tossed computer monitors, power supplies and such. This is an old tradition in ham radio, known as the "junk box". Such junk will likely have usable rectifier diodes.