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Sovtek Midget troubleshooting

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  • Sovtek Midget troubleshooting

    Hi all,

    I'm helping my brother out with his Sovtek Tube Midget head, and have an interesting set of symptoms, I thin. I was originally looking at it because it didn't produce any sound at all for my brother, but I was able to get some sound out of it, and see a little of how/when it would fail.

    -- The overall output level of the amp is quite low. Turning it up to what should be a very loud half-volume is a quite quiet decibel level.
    -- The amp will only produce any sound for any length of time if a very low input level is supplied, and then only on the Low input jack. I was testing this with my Fender Jaguar, and I was able to play it for a number of minutes without any trouble, while plugged into the Low with the guitar's bridge pickup on along with the choke-capacitor switch turned on. Turning both pickups on and the choke off, and then playing a chord hard, resulted in the amp becoming completely silent. I didn't hear any kind of pop or anything as it went quiet, it was more like it just turned off. I could hear the chord I played through the amp only momentarily, before it silenced itself.
    -- Powering the amp off completely got whatever had shut down to cool off (or something?) so that the amp began operating again, at the level it did when I started. Just putting the amp in standby for a similar period of time will not bring the amp back to a working state.
    -- Using the High input will cause the amp to almost-immediately shut down, just as it did using both guitar's pickups on the Low input.
    -- Turning up [clockwise] the Treble adjust knob turns the amps volume down. The amp is silent with the Treble turned all the way up/clockwise.

    I tried a completely different set of tubes, and that didn't make any difference. It does still have the original capacitors. Would bad caps cause these symptoms, or is there something else entirely I should be looking at?


    thanks for your time!
    - Justin -

  • #2
    It sounds to me like the Low input jack might be messed up.
    The High input runs through it. (a normally closed contact)

    Here is the schematic.
    mig-50h.pdf

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