Silvertone 1389 transformerless amp: looking for schematic

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by slidincharlie, May 25, 2008.

  1. slidincharlie

    slidincharlie Member

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    I have recently bought a tiny Silvertone 1389 amp.
    It's one of those old transformerless amps with 12AU6, 50C5 and 35W4 tubes.
    I need the schematic to check if the numerous parts replaced by some tech are correct.
    SchematicHeaven does not have it.
    Can anybody help?
    --Carlo
     
  2. SatelliteAmps

    SatelliteAmps Member

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    A 1389 has an output transformer, so it isn't really transformerless. I don't know of a schematic being available for the 1389, but the 1430 is an almost identical amplifier, and that schematic is on schematicheaven.
     
  3. slidincharlie

    slidincharlie Member

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    Thanks Adam.
    I have the 1430 schematic... which makes me puzzled, because the circuit in my 1389 looks very different! My amp has been clearly worked on by some tech, and it has quite a few more components than the 1430 schematic... :confused:
     
  4. SatelliteAmps

    SatelliteAmps Member

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    Any chance of taking a really good picture of it and posting it?
     
  5. slidincharlie

    slidincharlie Member

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    Adam,
    here's two photos:
    http://img.villagephotos.com/p/2005-9/1080251/DSCN0112.JPG
    http://img.villagephotos.com/p/2005-9/1080251/DSCN0117.JPG

    This is a link to the Silvertone 1430 schematic (which is a fairly similar amp), hand-drawn by a tech:
    http://www.clarkhuckaby.com/Images3/SlvrtBef.gif

    and here's the schematic of the same amp taken from another site:
    http://www.schematicheaven.com/bargainbin/silvertone1430.pdf

    The first schematic includes a variable cap that is not in the second (and is present in my 1389 amp).
    --Carlo
     
  6. teleamp

    teleamp Senior Member

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    From what I read, there are safety concerns with the B+ running directly from the incoming AC. I suggest that you use an isolation transformer, or have one installed in the amp if you are going to use it.
     
  7. slidincharlie

    slidincharlie Member

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    Mike,
    yes, I know what are the issues with such an amp.
    I'm searching for a stepdown isolation transformer, but couldn't find one so far... :(
    Thanks,
    Carlo
     
  8. SatelliteAmps

    SatelliteAmps Member

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    Hammond makes stepdown isolation transformers that are relatively inexpensive.

    The pictures look like most of the stuff is there. I'm not seeing a lot of extra parts in the amp. It does look like a tech replaced all of the capacitors and a few resistors. I think it looks like a few resistors were tied together to make a specific value, but that is about all I can see as far as extra. Is there something extra that I am not seeing?
     
  9. Jaybird03

    Jaybird03 Member

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    I went through the same thing you are trying, and finally decided to make the amp safe with a power tranformer. I had to change the tube setup to El84, 6X4, 12AX7. A Kalamazoo Model 1 circuit. Works great, sounds like a million, and still looks like a Silvertone.
    [​IMG]
    [​IMG]
    [​IMG]
    [​IMG]
     
  10. slidincharlie

    slidincharlie Member

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    Great job Jaybird!
    Too much work for my taste though...
    I was lucky to find a stepdown isolation tranny here in town.
    The amp works fine but have definitely some hum, that I'll try to fix (?).
    It has a recent Jensen MOD series ceramic speaker now. I guess I'll put a Weber alnico in there, I bet it will sound better.
    --Carlo
     
  11. slidincharlie

    slidincharlie Member

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    Adam,
    I checked my amp and it matches the first mod 1430 schematic (hand-drawn) perfectly.
    So I only replaced all resistors (they had all drifted). It works fine except for an excessive hum (but consider that it must be cranked to get some decent volume...)
     
  12. SatelliteAmps

    SatelliteAmps Member

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    Glad it sounds better. Excessive hum can be a few things on that amp. Have you tried flipping the polarity of the plug? On an amp like that it would make a lot of difference. Also, you should consider putting a three prong plug on it, which would help. Other than that, the next option would be to modify the amp to try to remove more hum, but I wouldn't do that until I changed the power cord.
     
  13. slidincharlie

    slidincharlie Member

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    Jaybird,
    did you put an 8" speaker in the amp?
     
  14. slidincharlie

    slidincharlie Member

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    Adam,
    I have already installed a 3-prong cord.
    Flipping the plug into the mains socket did not help (btw, sockets are not polarized here in Italy).
    The hum seems to come-and-go randomly.
    Anyway replacing the stock input jack with a shorting jack helped a bit: with the guitar plugged in the hum is lower now.
    Thanks,
    Carlo
     
  15. Jaybird03

    Jaybird03 Member

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    Yes I put in an 8" speaker. I cut a new, thicker baffle board and placed the speaker low in the cab.
     

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