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Repairing Old School Power Supply?

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  • #16
    Originally posted by boslab View Post
    I’ve only had one brush in 30 years it’s had 5 new handles and 18 new heads ( can’t remember the amounts, 2 Ronnies sketch very funny, of fork handles fame)
    https://youtu.be/pV1IP4N9ajg
    I’d hazard a rotted variac wire myself,
    mark
    I love that one too, had to go buy some "O"s the other day and thought of that sketch

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    • #17
      Originally posted by I make chips View Post
      Wow a selenium smoke generator!
      Yeah. Maybe not many have seen them these days, but selenium rectifiers, if they burn up, produce seriously toxic smoke.

      -js
      There are no stupid questions. But there are lots of stupid answers. This is the internet.

      Location: SF Bay Area

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      • #18
        That one from Rich C is a lot fancier than the OP's unit. Much of that fancy stuff probably is not present in the OP's.
        4357 2773 5150 9120 9135 8645 1007 1190 2133 9120 5942

        Keep eye on ball.
        Hashim Khan

        Everything not impossible is compulsory

        "There's no pleasing these serpents"......Lewis Carroll

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        • #19
          In my first few years in the electronics business, selenium rectifiers were common. And they all smelled like farts. Sometimes I'd see them bridged with silicon rectifiers- then the voltage on the filter caps would be higher than normal, sometimes causing problems. I do not miss them at all.

          If this plating power supply has them, it's probably safe to replace them with silicon rectifiers since you have some adjustability there anyway.
          I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

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          • #20
            go buy an old used sorensen DCS on ebay. anything made in the last 30-40 years will be smaller, more efficient and more reliable than that thing
            -paul

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            • #21
              That would do it. Probably not more efficient though, it's hard to beat a transformer with a voltage dropping regulator system.

              We need some pics of that old thang to see what's inside, just for curiosity if nothing else.

              Why all the hate for selenium rectifiers? They work pretty well, and on a per-junction basis, they are fairly low-loss, comparable to silicon. It's only when you need a number of junctions that a silicon diode really beats them.

              There now are better solutions for most useages, but they were very practical and inexpensive semiconductors at the time. They still can be for low voltages and high currents.
              4357 2773 5150 9120 9135 8645 1007 1190 2133 9120 5942

              Keep eye on ball.
              Hashim Khan

              Everything not impossible is compulsory

              "There's no pleasing these serpents"......Lewis Carroll

              Comment


              • #22
                Selenium rectifiers have a forward drop of about 1 volt per cell, and each cell can only withstand about 25 volts, so I don't see how they can be considered more efficient than silicon rectifiers. Germanium has even lower forward drop, as does Schottky. For the ultimate efficiency in low voltage rectification, active rectifiers constructed from MOSFETs are best.

                Click image for larger version

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                Paul , P S Technology, Inc. and MrTibbs
                USA Maryland 21030

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                • #23
                  At the risk of de-railing the thread, I've just discovered some instructions for building mains rectifier diodes from aluminium rod and lead sheet in 2 lb. jamjars of potassium phosphate solution. There are four of these arranged as a diode bridge, with carbon filament lamps used as volt droppers on the output. There's no attempt whatever to cover or insulate any of the terminals or wiring. Electrical safety? What's that?!

                  I've never heard of this chemistry being used to make a diode. Has anybody else ever come across it? It's in the Boy's Own Paper of August 1920 if anybody wants to look it up.

                  George

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                  • #24
                    You can heat up some copper sheet to form a kind of scale on the surface to make a rudimentary solar cell
                     
                    Helder Ferreira
                    Setubal, Portugal

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                    • #25
                      Originally posted by PStechPaul View Post
                      Selenium rectifiers have a forward drop of about 1 volt per cell, and each cell can only withstand about 25 volts, so I don't see how they can be considered more efficient than silicon rectifiers..............................
                      Not "more" efficient, but not significantly "less" efficient on a one-to-one basis junction-wise. Most silicon are theoretically 0.6v and in practical realization, have one volt forward voltage under load.

                      For any usage that has high current and low enough voltage to use a single junction, selenium can be practical enough. High current silicon diodes are not cheap.

                      Schottky and germanium are lower forward voltage, yes. Schottky are also high frequency, usually not used for bulk current usages, and germanium is not very popular these days for a host of reasons.
                      4357 2773 5150 9120 9135 8645 1007 1190 2133 9120 5942

                      Keep eye on ball.
                      Hashim Khan

                      Everything not impossible is compulsory

                      "There's no pleasing these serpents"......Lewis Carroll

                      Comment


                      • #26
                        Why all the hate for selenium rectifiers?
                        I vaguely remember as a kid that the plates also had some photo-sensitivity, and could be used as a very low efficiency photocell. Scavenged from the back of defunct TVs.
                        "A machinist's (WHAP!) best friend (WHAP! WHAP!) is his hammer. (WHAP!)" - Fred Tanner, foreman, Lunenburg Foundry and Engineering machine shop, circa 1979

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                        • #27
                          If it was a real antique DC power supply it would have a nice mercury arc rectifier!

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                          • #28
                            I had a 12v battery charger with one of these
                            You may only view thumbnails in this gallery. This gallery has 1 photos.
                            Helder Ferreira
                            Setubal, Portugal

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                            • #29
                              Ah! The Tungar valve!

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                              • #30
                                Originally posted by Gazz View Post
                                I have a need for such a thing now but I can't get any volts out of it, even when its plugged in!
                                Did you check the status of the fuse?


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