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Motorola where do start question.

Discussion in 'Tube Audio' started by MagnoRichard, Sep 16, 2018.

  1. MagnoRichard

    MagnoRichard New Member

    Messages:
    3
    Hello all
    New member. New to the hobby.
    I literally found a 1961Motorola stereo console with record player and radio in pristine condition at the local dump. Took it home, plugged it in and worked like a champ. Unfortunately, after warning my wife not to leave it on because of over heating,you guessed it, she left it on and it overheated and no longer works. Where do I go from here? The amp is a HS-839A. I tested all the tubes in the stereo and they checked out. I bought a second HS-839A online but to no avail so I suspect it has something to do with the pre-amp, but what the heck do I know? Your advice is greatly appreciated.
     

     

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  2. century tek

    century tek Super Member

    Messages:
    3,340
    Location:
    The Evergreen State
    Hi and welcome!

    You can leave them on and they should never over heat. Remember, tubes were a part of our lives up until the late 70's when they began to get phased out by solid state technology. We had tube tv's and stereo's in our house growing up and they were left on 24/7.

    If you are not getting any power, it could be a fuse. On a lot of those Motorola's, the amps had the fuses hidden under the chassis. Also, a lot had those circuit breakers. Check for an open breaker by pushing it in and see if it clicks. If it does and then shuts down again, you have other issues.

    Usually a power problem is the simplest to diagnose. If the amp has a fuse and it is blown, the preamp will not work as it gets its power from the amplifier.

    If you can, show us what you got.

    EDIT: If it has a fuse or circuit breaker and neither are good, then you have other issues such as a shorted capacitor or 5U4 or 3DG4 rectifier tube. Power transformer is not really suspect until all the other things have been checked.
     
    Last edited: Sep 16, 2018
  3. MagnoRichard

    MagnoRichard New Member

    Messages:
    3
    4B0A3760-0E3A-4671-917E-838BBA575B8F.jpeg
    Thanks for the quick response. I grew up in the audio Stone Age. Maybe the overheating issue had more to do with wasting electricity or burning up the tubes. Anyway, I could not find a fuse and the circuit breaker clicks. When I plug in the amp is there an alternate way to fire up the tubes to test the amp? When I reconnected the electrical components both the amp and pre-amps still didn’t fire up,however electricity was flowing to the rest of the system. Could it be something as simple as an on/off switch? Also, on the pre-amp schematic it reads “close gang before replacing tubes or pilot lights’. What is this referring to?

    Many Thanks for the vintage Audio 101 lesson.
     
  4. century tek

    century tek Super Member

    Messages:
    3,340
    Location:
    The Evergreen State
    You just have to know which wires to jump to get the amp to turn on by itself.

    Yup.

    The tuning gang is actually the tuning capacitor. If it is open or all the way to the end of the dial in one position, it probably makes it hard for you to reach your hands up there to replace the dial lamps or pilot lights. If it is closed, it makes it easy to replace them.

    I know you say that you are new to the hobby, so you had better go out and get a basic volt/ohm meter. A volt meter will be able to tell you where the power stops even If it stops at a broken switch or an open fuse.
     
    Last edited: Sep 16, 2018
  5. knockbill

    knockbill Addicted Member

    Messages:
    7,782
    Location:
    SE PA
    Do you have a meter to check voltages? You'll need one to follow the circuit to see where it stops... to run teh amp out of teh console, you need to jump the switch connections on the amp... post the schematic, if you have it...
     
  6. MagnoRichard

    MagnoRichard New Member

    Messages:
    3
    I do have a volt meter, however I need to detach the pre-amp from the console in order to get to the switch. This may take some time. Thanks Everyone for your comments.
     

     

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  7. primosounds

    primosounds SE KT120 w/ 6J5G drivers. Subscriber

    Messages:
    2,715
    Location:
    Terra, 21st century CE
    Yeah, if you are going to try and repair this then some basic electronic instruments and tools would be most useful.
     
  8. safebet

    safebet Long live vintage! Subscriber

    Messages:
    225
    Location:
    New England
    You know more than you think but start with the basics. Follow the advice provided by other members above.

    If you obtained a spare HS-839A chassis (working, key attribute here), fully connected it and the console does not work, I would check the AC power cable chain that runs throughout these consoles. The cable typically is a flat 4 pin connector that connects through a tuner or pre-amp chassis and terminates at the turntable. It's purpose is both to supply AC to each device on the chain and provide a means for any of them to close the appropriate pair to power on the amplifier. With this in mind it could be a bad power switch, yes as you suggested, at the pre-amp, but also the turntable could power the system on so it may be a loose connector too.

    The SK-70 console in my avatar uses an HS-960 chassis very similar to yours but has a much smaller power transformer; your amplifier chassis is designed to connect to and provide filament/plate power to a separate tuner/pre-amp. The tuner in my SK-70 has it's own AC power transformer and as such uses the 4 conductor power cable scheme I described. Another HS-960 difference is that audio runs through the "umbilical" cord connector. Where yours has separate phono jack style connectors it's likely power is controlled through that umbilical cord. In this case it may get a little more tricky but the concept is the same. The point is to trace AC power first, something easy to do and most likely the issue.

    My console is very reliable and gets played often. The single ended L&R output stages may provide only a few watts of power but they sound great! Better in my opinion than the push pull 6V6 pairs in the fancier model in the guest room:


    [​IMG]
     
    Last edited: Sep 29, 2018

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