Electro bench power supply

I just looked at one I have here & it uses "pellet" type rectifiers. Quite unusual.
I have also seen them use the "press fit" type rectifiers, like the car alternators use.

These are stud mount.  I can't see the numbers, though.  I'll get out my big lighted magnifying glass and see if that helps.  The reason I was calling the rectifiers selenium is because that was what my stepdad called them.  I had not laid eyes on them until the other day.  Frank posted some information that got me to looking more closely.  They for sure are not seleniums.  That is also probably why they might still work okay.  These rectifiers are mounted in huge heat sinks.  I'm going to try to get my pictures to load.

FrankB wrote:

A silicon diode of the amperage rating he has would be typically a stud mount.
I have never seen a leaded 20A diode.

Neither have I. I was trying to explain diode through in an easy to understand way. Because he didn't know the difference between silicon and germainium. And I was explaining the physical differences, and the way he was talking, it needed to be clarified.
An I too went on the assumption they were Selinium.

I have worked on 3phase 12 and 24 volt 100 amp NTDS power supplies. I found errors and reported those and suggested changes. Those power supplies had what is called battle short. That's when things get hairy during incoming fire that destroys wiring in the ship or essential electronics to control all defensive systems. It had a battle short switch which would continue to supply power even while it was goingn up in smoke just to keep the system running and bypassing normal fuses.

Would you believe the factories didn't wire them right, they should have known but  it was overlooked. They had the SCR BANKS wired wrong. So I wrote up a descrepency report and the repair solutions.  Got a nice bonus from NAVSHIPs write-up in a publication called EIBS (Electronics Information Bulletin).I really surprised our Shop and all the suppervisors.And a $1200 beneficial Suggestion Award. I think I have a 200amp stud mount diode somewhere around here. And a diode that was sawed with a bandsaw. The flange on it is about the size of a $ .50 piece.

Wildcat-
Can you see the numbers on the diodes? That can be looked up to get the ratings.

You can measure the AC going to the diodes, & we can figure PIV needed from that too, if you can't see the numbers.

A silicon diode of the amperage rating he has would be typically a stud mount.
I have never seen a leaded 20A diode.

How to Insert Photos?:
Please click on FAQs at the link at the top of the page its the first one listed.
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 By the way selenium rectifiers are usually square and have many of the square fins or plates, there are some that  round disks that are also stacked but they are usually used in industry before solid state diodes came in to use.

silicon diodes are smaller than most small wattage resistors of say 1/8 watt and have axial leads.

Here's a pdf file that elaborates the differences --> Diodes description Click Here

In an earlier post, I put a question mark in parenthesis when talking about the selenium rectifier in this power supply.  I have some silicon rectifiers here, and the ones in the power supply look like they might be silicon rather than selenium.  This finding may stand me in better position than I feared.  If they are silicon and put out correct voltage (whatever that is!) I should be golden in that regard.  I wish I could remember how to post pictures....

I don't have a problem with output voltage, at least for 12 volts, which is the most I need for an old tube car radio.  My thinking at this time is that the rectifiers are probably okay.  Taking the thing all apart is the biggest headache so far.  I appreciate your taking the time to explain this stuff to me, Frank.  It was good of you.  I did not get a response on "the expert forum", so your taking the time to respond is appreciated.  That no service information exists is rather unnerving, but perhaps we can get thru this and get it back up and operating for another 50 years.

You might try Fair Radio Sales in Lima Ohio or... RE-PC in Tukwila WA. They had a good used cap selection, last I was there, like 2 yrs back though. Also some pinball parts suppliers have caps in that range.

BTW- If the filter is rated at 40V, and your output is 32 max, I would go with a 50-60 v or higher cap, just on general principals.

Keep in mind you could always parallel caps if you can't find the 12Kmfd ones.
That might actually be cheaper in the long run.

To check a selenium, you use an ohmmeter just like checking any diode--except the readings will look odd compared to silicon diodes.  Should show low one way and high the other.

In reality, the best test is to check the voltage coming out of them. 

Now if you have to replace it, the OEM will be unobtanuim to find. Most folks use silicon diodes. Be sure to check the voltage if you use them, as it will be higher than the original rectifiers, necessitating a higher voltage filter cap.

If they are hooked to a heatsink & you need to replace, check the hookup config.
You may need a silicon diode that has rev. polarity on the mounting stud for one rect, depending on the original arrangement.

How do I check the selenium rectifiers as has been suggested?  And what would I replace them with if need be?

This old power supply belonged to my stepdad.  He used it not only to repair car radios, but actually ran a car radio on his bench as his shop radio.  So, yeah, I believe it is fair to say that this old supply has lots of hours on it.  I used a '54 Buick radio as my shop radio for a time and used this old supply to power it.  For days on end at times.  If the date code on the cap is 1966, that is the closest I have come to dating this thing.  Thank you for that and for your information guys.  I may get this thing going yet.  There is nothing available in the way of service literature I have found anywhere.

It will be easier to restuff the existing cans than it will be to try and change clamps in this case.

You can install those caps you mentioned and if the hum is still objectionable add an additional one across the output terminals. Experiment and see what happens.

Yep,

12,000mf/40 volts.

I worked with linear computer supplies for industrial controls in the early 80's these do not necessarily leak but loose capacitance, their ESR goes off. In the application the supply not only powered the driver board but also 24 volt solenoid for air cylinders. The machine would start to fumble product. Tagging the supply with a scope set for 1 second sweep would show dips in the 24 volt out as the machine went through its cycle. Doing no more than replacing the large cap about 3" diameter by 6" tall solved the problem.

Again look to a computer cap, Digi-Key may still sell these, hope you don't have to go to Newark or Farnel...

Stuff them what a hellacious of a waste of time. The capacitor date code suggests 1966.

Get the diameter of the new cap and look up a capacitor clamp of the correct size. Re-use one bolt hole if possible and drill a new hole in the base. Or drill two new holes if the old cap was mounted with a strap. Straps are available the correct diameter too.

Pilot light was probably a neon with resistor as a one-time module. For a neon to expire look at 5k+ hours. That old supply has been around...

Better check the reverse leakage of the selenium rectifiers under load. Leaking AC could raise heck with new caps...

YMMV

Chas

If I remember there is a guide somewhere on sizing capacitors to current requirements.
I don't remember if it was online or one of my books. Ill look around. No promises.

I found some more information.  I managed to get the larger of the filter caps out of the chassis.  Here is what I found on the capacitor can:

SPRAGUE

POWERLYTIC

36D

12000-40DC

RED  POS

6680

This filter cap can is 4 1/4" tall and is 2" around.  It has two terminals on top.  They are held on with minus head screws.  One wire is red, one wire is black.  I took some pictures, but I'm having trouble posting them.

Does this mean I need a 12,000 microfarad, 40 WVDC electrolytic capacitor?  Being poorly filtered should not be a concern.....



Edit:  I have looked on Digi-Key and Mouser's sites.  Mouser's says they are out of stock, and I'm having trouble navigating Digi-Key's site.  I believe they have them in Cornell-Dublier at approx. $12.00 each.  The new ones are smaller physically than the old ones, so I can stuff the original cans with the new caps, which will allow everything to look original.  I am going to take this thing the rest of the way apart, clean well, and fix the broken pilot light.  It has a red one now that you can't replace the bulb in.  I'll modify the hole for the big type that the bulb is replaceable in.  I'm assuming a 120 volt bulb, but measuring voltages should tell for sure.  The pilot light is powered directly off the main power fuse, hence my thinking it is 120 volt.

Let me clear up a couple of misunderstandings.  My fault, so I apologize for the confusion.

I am working on an Electro model NFBR variable-voltage battery eliminator DC bench supply.  I am not working on a Buick radio, per se, just using one to test the power supply.  Let us not worry about the Buick radio just yet.  My questions pertain to the Electro power supply.  I have not found any service information on it.  I tried Radio Museum and Bama and everyplace else I could think of.  I have some pictures and will post them.  I need a guess as to the capacity of the two big capacitors in the power supply.

I would say concerning your radio capacitors that the microfarads value can be as high as 40mfd
Usually the larger value is first then a current limiting resistor of more than 1Kohm then the smaller value.
This of course is on the 6 or 12 volt power connection.
I haven't tried to download the schematic from radiomuseum.
If you don't find the exact schematic look for one that has the same tubes and same tube count and you should be safe on using the capacitors shown in the schematic. Most radios were under a license from RCA or Hazeltine. So the designs they used for production were the same.

I will see if I can download one of them, just be aware that the downloads are limited to I believe 1 a day to 3 Maximum a month, so be judicial in your picks. Of course if you become a member ( yes there is a yearly fee ) you have more privilidges for downloading. It does take some time before you become a member though.

Sometimes the cans had the printing on the black paper can covering, if yours has that or under it if they are the slip on insulating covers.
Can you post pix? It would help.
 The Candohm is just a brand of resistor, typically with a metal shell riveted to the chassis for heat dissipation. They almost always have a part # ot value printed or stamped in the metal on them, often hard to see because of their mounting. It will be on a side, not the bottom.

Try radio musium.type in the word Buick in thier search box.
[You must be registered and logged in to see this link.]
Anywhere from 5 to 15 ufd. On cap value just a guess.
They have several free schematics in 1954-56 range.
You also try a search whilst there on your power supply.

The power supply has two can capacitors.  They appear to be single caps, not multiple caps in each can.  The radio I was running with the supply was an old tube 1954 Delco 481500, made for a Buick.  This supply calls itself a "filtered and regulated DC supply".  The problem I'm having, outside of not knowing what I'm doing, is that I do not see any markings on the cap cans to tell me their value.  The resistor I called a candohm is in the power supply.  I have taken some pictures and that might help.  Everything about this old power supply is massive.  I have not been able to find any kind of information on this thing anywhere.  Any guess as to the value of those two big caps?  I'm going to do some voltage measurements to see what kind of voltages I'm dealing with.

Does the power supply have capacitors? Or are you talking about the radio. Since it runs on a battery then and has filter caps it I am assuming it's a farm radio. Those may have a vibrator. If that isn't the case they would require a B battery.
It would help if you separate topics.
One on the power supply then state the radio in another paragraph.
Because I wondered if your power supply had the candohm or radio. I know better it's the radio, but newbees might have no experience.

Caps that are bad can short the power supply and leaky ones will drain the voltage down as the get older more and more and less and less filtering. To the point for becoming a short.


Older power/battery supplies did not have good filtering and just as a note they were half wave for the most part.
And they shouldn't be used on the later hybred and solid-state car radios.

Frank is right on about the filter capacitors. Old caps in the supply circuit side of it will dry out the electrolyte and show what you found out with resistance readings.

450 volt caps would be a good replacement, if you replace one it would be wise to replace the other one too. Are the caps cans or axial type. If there cans which I doubt, they may have multiple caps inside.
Get caps of the same or next higher closest capacity. If you can't find the exact value that's OK. JUST MIND THE POLARITY.
Most caps of that era had a wide tolerance capacitance value but usually were 20% or more.
Please keep us informed of your progress.
Sal's capacitor web page is your best bet when buying them.

What effect would leaky or almost shorted filter (?) caps have on the output of this supply, do you reckon?  And where would I start guessing as to capacity of those two big caps?  One is bigger in size than the other, and I realize physical size is no indication of anything.  I'm thinking that 450 volts should be safe for working voltage.  Nothing in there should be above line voltage.  There is a candohm resistor that runs across the entire chassis, about 10" long, and is about an inch in diameter.  There is a
n "Adjust-a Volt" Variac that only puts out about 35 volts, apparently due to that big ceramic resistor.  There is a voltmeter and an ammeter, along with a burned out pilot light and a power switch.  That is really all there is to this thing.  I can't find any information on this thing in the usual spots.  Bama, Sams, Google.  I even asked on ARF, but have not gotten a replay as of yet.  There is one of the same model for sale on ebay, but apparently it is somewhat newer as the front of the cabinet is painted fancier.  Mine may have been military, so that is one difference.  If I had a close guesstimate as to the capacity of those caps, I could probably punt for the  rest.

Yup 1K is way too low.

I checked the selenium (?) stack like you suggested.  Looks okay to me.  I'm a total rookie at power supplies like this one.  I've had the thing thirty years, but I have just left it sit on the bench and do its job.  My theory is the filter caps are allowing positive voltage to appear on the negative lead, which is causing the vibrators in the car radios to go wonky.  I'm going to have to take this thing totally apart to do whatever I need to do.  Unwire things.  I am taking detailed pictures and am going to draw a diagram.  This will be easy for me to miswire, particularly if I can't find a schematic.  The filter cap cans are not marked that I have been able to see.  I unplugged the filter caps and checked them with an ohmmeter.  They check nearly dead shorted, only about 1000 ohms and they don't charge like they should.  I don't have a capacitor checker, per se.  I was taught to use an ohmmeter to check caps.  I can't actually measure capacity, but I can see if they charge and what their resistance is.  I was taught that anything less than several hundred thousand ohms was cause for suspicion.  Poor people have poor ways, I guess.

The problem is in the power supply.  Using a car battery completely eliminated the buzz.  I have the PS cover off.  IT will be a pain to work on.  Very heavy and a everything is held on with bolts that I can't see the nuts for.  I don't see a value on the electrolytic caps.  Does anybody know of a source for a schematic?  Again it is a model NFBR.

I just remembered that if they are stacked seliniums, the bolt & nut compressing them together can work loose after a while from thermal ratcheting, and can cause some odd issues.
 It's possible that tightening the bolts holding the rectifiers together may solve the problem.
 It's conceivable that a loose stack could cause poor rectification & the hum.

(Of course... it could be hummung because it forgot the words to the song too.  )

Thanks, Frank.  I'll experiment some and let you know what I find.

Your problem might be filters in the PS.

 However, over the decades, I have worked on a number old car radios that require a pure DC supply, aka battery, to work without the noise.

  Now SMPS in computers, the new smps ballasts in flourescent lites, etc, can cause the noise too.
 Try the battery first or unplug the computer, turn off the lites etc.
Try to isolate it first.

This Electro power supply is model NFRB.  The problem I'm having is a noise in car radios.  The noise appears in the audio.  It is a buzz that is the same frequency as the vibrator in the radio power supply.  I only hear the buzz when the antenna is plugged in to the car radio.  When the antenna is plugged in to the car radio, the buzz also is heard in my bench radio, a Hallicrafters SX-110.  When the antenna is not plugged in to a car radio, there is no noise in the audio at all.  What symptoms would I experience if the filter capacitors in the bench supply were leaky?  I am going to try using a 12-volt car battery in place of the bench supply to see if that makes a difference.  If it does, I need to look further into the bench supply.  If there is no difference, then the noise is coming in thru the antenna.  I am using a car antenna like you get at a parts store, mounted on an "L" bracket, fastened to the metal on the facia of my garage, on the highest point of the gable end.  I am using the standard lead-in, with one extension.  Whatever is causing the issue, it is a recent development.  I have used this setup previously with no problem.  We had guttering installed on the garage and have had the facia and soffits covered in aluminum last summer.  Any ideas?

I have an Electro bench power supply for operating car radios.  It will put out DC, variable, from 0 to 32 volts up to 20 amps continuous.  The thing weighs a ton and has two huge selenium rectifiers.  I believe I need to recap this supply.  Have any of you had experience with one of these monsters?  It is not only infinitely useful, but was my stepdad's, so there is the family heirloom dynamic.  Thanks.