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Old turntable old axial electrolytic

Discussion in 'Power Electronics' started by frontier9, Mar 29, 2021.

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  1. frontier9


    Mar 29, 2021
    So - 1974 turntable - an SL-55. I took out the transformer for 100v (japan) and here it's 220v so I tested in isolation and measure 39v secondary coil. So I guess it's an 18v - and the DC motor is 18v on sticker. So replace with a new transformer. It has a rectifier thing, can't see the diodes but didn't fully dismantle it to understand it all. I'm still new to messing with things I didn't build myself so asking for advice.

    Has an old axial 470uF axial cap for smoothing AC i guess. Thats 50 years old - it still has measurable capacitance. Thing works after transformer change out - I'm only an enthusiast who makes amps and power supplies. So tell why I shouldn't do this:
    1) solder in parallel a new 470uF (50v) with the existing cap. I figure if the resistance of that goes up it will just mostly use the new cap and bypass old one. Then I don't have to de-solder the old one.
    2) if I did change out the old cap why not throw in a 1000uF or higher?

    It has a voltage regulator IC that looks pretty much like a modern one, I didn't read the writing on it yet. Any reason I should replace that - would that improve anything being a modern one?

    I put a 2amp transformer in - the old one seems, by size to be 0.5 to 1 amp max. Does putting a bigger transformer require any change? Anyway, when I power it on/off (by merely selected it works fine so I guess if things were going to go wrong they would have already.

    Next plan is to make a phono pre-amp and put it inside the very spacious area under the bonnet (upside down) of this unit. This thing seems really rare and there is a manual website that has seemingly every manual ever - including turntables. This thing doesn't have a manual on there. This manual seems a lot like what I see in this one if anyone cares. Nice how old manuals have circuit diagrams etc.
  2. Harald Kapp

    Harald Kapp Moderator Moderator

    Nov 17, 2011
    Welcome to EP.
    Capacitor: better replace the old one. Don't want to risk leaking electrolyte to create havoc on the pcb, do you?
    Regulator: Why replace it if it is good? I doubt you will find a new regulator improves anything.
    Transformer: No problem with the new transformer being more powerful than the old one. The motor and electronics will draw only as much current as they need.
    I fully agree. Alas not only do modern manuals not contain schematics - you mostly cannot get schematics at all :(
  3. frontier9


    Mar 29, 2021
    So helpful .. i doubt it will leak onto the PCB due to it's separation and orientation but ... point taken, if it does fail who knows.

    On my other equipment I have things like NTC thermistor for inrush protection/prevent some start noise. Just made me wonder if the bigger transformer would matter but yeah - it is just a source - size doesn't matter so much eh. Thanks.
  4. Martaine2005


    May 12, 2015
    Replace the old capacitor. It may not leak directly onto the PCB but it sure can go short circuit.
    Is it worth not doing?

  5. frontier9


    Mar 29, 2021
    Yeah i guess if it did that having another in parallel wouldn't help ... but I've heard that an electrolytic tends to go high resistance if it goes dry. Isn't it more like small surface mount tantalums that fail into short circuit.
    I'm going to replace it ... so point taken.
    Thanks Martin
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