I'm working on a Jewel 500, schematic here http://www.nostalgiaair.org/PagesByMode ... 009718.pdf and I'm going to replace the selenium rect. On the schematic there are no values for voltage. So what should my goal be if I replace with a 1N4007 and resistor? What voltage would be normal?

Thanks in advance.

Is the original Selenium rectifier already dead , or are you replacing it as a future reliability modification ? Because if it isn't dead yet , just do your normal recap , and then measure the voltage .... If it is already dead , and the schematic has no voltage specification listed for the B+ , you could always check a few schematics from other "AA5" type radios and go for an average of their listed voltages .... Except for the selenium , the rest of you set looks , wiring wise , just the same as any other set that uses the 50L6 output tube , so any other set's specification that uses that tube would probably be close enough to produce acceptable results ....

... If ya really wanted to mod the circuit , you could always go the other way , and install an octal socket and use a 35Z5 rectifier tube !

It would be really easy , since there is already an octal socket sized hole in your chassis , as it was to originally use the 35Z5 before the manufacturer switched to using the selenium ... You would just remove the "selenium adapter plate" thats in the info you linked , and then rewire the tube's heater circuit to include the tube rectifier . Again , you could simply copy the circuit used in any other "AA5" set that uses the tube rectifier , and you'd be all set ....

Hope this is helpful:

http://www.w3hwj.com/index_files/RBSelenium2.pdf

Rich

It is uncommon to use a selenium rectifier with that tube lineup. Few sets to compare against.

Short answer: my opinion, don't replace the selenium unless B+ voltage is significantly less then about 100 volts DC.

Long answer: if you are determined to replace the selenium no matter what, read this for insight:
http://w3hwj.com/index_files/RBSelenium2.pdf

THanks for your help!

In as few words as possible:

ALWAYS replace a selenium, no matter the voltage.

They are ticking bombs, just like trying to get away without replacing electrolytics and paper caps.

Carl

Not the same consequences to replacing caps/resistors and selenium rectifiers.
The user needs to understand a bit about power supply design and why I linked to the PDF for more guidance on what to plan for.
My opinion was geared towards newbies who may not understand or get the hand holding that is needed.

Dale, I saw that pdf you linked and even have a copy in my files. It's what actually got me started on the road to replacing the SR.

Burnt Fingers, I am replacing the Sel. Rec. due to the recommendations in the pdf and several posts I've read on ARC. Even is the SR is good and has a lot of life left in it, replacing it will be a learning experience and that's where I'm at right now.

If you don't have a parts list, is there a sure-fire way to distinguish between a selenium and a copper-oxide? (Although the latter probably need replacing too.)

Dave Wise

Copper-oxide rectifiers were too expensive for consumer products (other than their use as instrument rectifiers in AC meters). But as to their appearance, they're more heavily built than selenium rectifiers, use more clamping pressure, have copper washers showing, and usually have round plates. They're usually still good, too.

Thanks, Alan. During my formative years I picked up a silly notion that the orange ones were C-O and the gray ones were Se, and I still have to make a conscious effort to think otherwise.

Dave Wise

By the way I have eight of the small bridges, if anyone has a use for them. I've never found any. They won't handle much current, I'm pretty sure (way under an ampere).

Thanks even more, Alan. Now I'm sure every power rectifier stack I've ever seen was selenium; the next one will go straight in my crosshairs.

Dave Wise

You dont need to replace those seleniums if they still work . I have been at this for over 40 years and have never replaced a single one .

Selenium rectifiers were made in nearly every color of the rainbow:



As to whether to replace or not, I guess it depends on your viewpoint.

A component with a known aging mechanism is more likely to fail. The consequences of a selenium failure could be (not always) a smoky, nasty cloud of smelly vapor. Seleniums usually fail by overheating as leakage and forward losses increase due to aging. Given that it's likely to fail and the failure is nasty, I would replace them. I certainly replaced bad seleniums when I worked in a TV/Radio service shop between high school and college.

It's generally accepted practice to replace old electrolytic capacitors, even if they are still working. So, I do the same with selenium rectifiers.

But... it's your call.

Rich

We all know your "restoration" philosphy which thankully to new owners of radios is in a very small minority. You must be proud of the money you save on caps, seleniums, resistors, etc.

The new parts dont cost that much , Thats not the deal . Its in understanding and knowing when to not replace parts unnecessarily just because 10 people said to replace them . Some people will never understand .

I still say , , that if I were going to convert it , , I'D convert it back to a 35Z5 , and make it a true AA5

I'm just not so sure I'd be in a hurry to convert it either , depending on conditions . If I were reasonably sure the unit wasn't mechanically compromised in some way , , and I had eliminated the chance of it feeding into a short circuit by doing a total recap of the radio , , and I put a small fuse in the circuit to cut power before any short got bad and hot enough to let out the putrid stink , , , I just might leave it . I know the one or two I've ever seen release the noxious stench were left energized long after a fuse would have blown , and so a fuse really would work here ....... Now , if I saw any rust or even any discoloration on the paint , , or any struck and bent fins , or any signs of excessive heating of any kind , , oh yea , I'd yank it outta there in a heartbeat .... And then I'd install the tube in it's place

Bottom line , yea , the op might as well go and do it , since it sounds like he has made that decision , , But just think about a nice warm tube VS a cold hearted , soulless diode ......

This endless debate will go on and on.
As a professional restorer/tech, I opt to make sure my customers don't come back at me because of leaving in an aged part prone to eventual failure - and probably costing them more money and a repeat trip - sometimes several states away.
People pay me to do work, not gamble with "what ifs".
They want peace of mind...... period.
I do the job, professionally, and their trust that I do the job right without cutting corners is of utmost importance, and reflects on my reputation.

I wouldn't think anyone else wants to gamble with a prized possession, family heirloom, or even an ebay purchase.

Generally agreed. I have on occasion left properly-working (i.e. still providing near-original voltage) selenium rectifiers in my own equipment but I would never leave them in there when working for someone else. It's just not worth the chance - and, Ken G, I have in fact have seen several failures over my 40-ish years of working on electronics of various sorts. Including one that wound up with flames, fortunately caught before it caught the rest of the house on fire. They usually *do* work but it only takes one failure to screw the pooch.

Brett