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  • EEVblog #649 – Power Designs 2005 PSU Teardown

    Posted on August 5th, 2014 EEVblog 18 comments


    What’s inside a 1964 vintage Power Design 2005 Precision Power Supply?
    Schematic HERE
    Forum HERE

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    • jim hatch

      Nice review.

      I have one or two of that brand around. Not precision.

      What I took note of was your description that the to-3 transistor was dissipating the full series pass wattage.

      In my greybeard test equipment repair days, My unit was marketed as “this design dissipates the heat outside of the cabinet”.

      In my unit, there is a big resistor mounted in a cage behind the unit.

      The series pass transistor would be in parallel, and just ” trim” the voltage drop.

      Now you have made me want to keep them for display.

      Looks like I will never clean out my man cave in my lifetime.

    • Synthetase

      Fascinating. That looks like a Sziklai pair rather than Darlington series pass configuration.

      • http://www.eevblog.com/ Dave Jones

        Yes, also known as a complementary darlington which is how I’ve always heard it called.

    • Zsola

      R83 Cal resistor, without value. Hmmm..
      Synthetase: thank you, another famous Hungarian, Sziklai György! :)

    • Eric Swartz

      I kinda started collecting these. Have five here on the desk right now (2 of newer design). I like to clean and calibrate them. They are not very precision until you clean the switch contacts really good. Then they are spot on.

      I bought a few for about $15 in not working condition. They came and worked perfectly. That was a disappointment :)

      • http://www.eevblog.com/ Dave Jones

        Sorry for your lack of good fortune :->

        • Eric Swartz

          Well, they did need cleaning, calibration and some of the lights replaced, so it wasn’t a complete loss…

    • Eric Swartz

      You can take the oven apart pretty easily. Just undo the 3 screws on the bottom, Twist and pull up the red can. Then you can pull out all the circuitry inside. It is on a board with a connector. There is a lot of insulation in there (asbestos? or glass fiber) though.

      • http://www.eevblog.com/ Dave Jones

        Ah, I just assumed it would be sealed in some way.

    • Mission Engineering

      Nice. That looks like a turret board. Some tube (valve) guitar amps are still wired this way today!

      • http://www.eevblog.com/ Dave Jones

        That’s the name I was looking for!

    • Johm

      Dave I would appreciate one of your Fundamentals Fridays about transistors, an insight on what the figures on their datasheets mean and some “traps for young players”. If you want to add some transistor configurations then better too! Thanks (:

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    • Michael Bo Madsen

      I was only 4 years old when the power supply was manufactured. I would
      love to see more, because it looks like the same as the first transistor
      electronics I designed as a teenager in the late 1970s, and improved
      later when I got to know the 741 ic. after that, my cheap analog
      multimeter no longer sufficient to measure the improvements. Try to zero
      trim using the R39

    • Workshopshed

      I know those boards as “Peg boards” but I don’t have a beard at the moment so I could be wrong.

    • Syd Jessop

      Maybe be a bit more forgiving of more modern constructions that have components hanging upside down with stretched out wires all higgledy-piggledy if you think this looks lovely, Dave!! It is not often the looks inside the box that count, you fickle creature.

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