Interesting old Univox amp, question

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by bob-i, Aug 22, 2006.

  1. bob-i

    bob-i Member

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    A friend found this old Univox bass amp cheep, only it didn't work properly. I ripped it apart and found that the impedance selector was fried. I disconnected it and hard wired the 8 ohms tap and it sounds great. All it needs now is cleaning of the pots.

    http://schematicheaven.com/bargainbin/univox1050bass.pdf

    I found something interesting. The chassis isn't grounded!!!. All power grounds are run to the first filter cap which is floating.

    The controls are grounded to the input jacks.

    So the question is should I ground the power after putting in the 3 pronged plug or leave it floating?
     
  2. donnyjaguar

    donnyjaguar Member

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    Get rid of the 5n capacitor on the input line and ground the whole chassis to the center tap of the power transformer.

    I'm going on the assumption that the chassis isn't live, which given the presence of the power transformer is fair.

    This looks like a good design. I hope the output transformer is big enough to take the power the 4x6L6 tubes can serve up.

    DJ
     
  3. bob-i

    bob-i Member

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    Yepper.... first thing I'll do is replace the 2 pronged power cord and remove that cap. I'll put a ground lug on one of the PT mounting bolts and ground everything to that. Thx, that was my big concern.

    Correct

    Seems to be. The impedance selector wasn't though, it's actually melted!!
     
  4. bob-i

    bob-i Member

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  5. esoteric pete

    esoteric pete Supporting Member

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    those old univox bass amps usually sound frikken awesome! ill bet this one is no exception!
     
  6. bob-i

    bob-i Member

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    Yep. Gutsy and clean.

    There's an empty punchout for another tube. Looking at the Univox schems it appears that they used the same PT for several amps so I'm confident that I can power another tube fine. I'm thinking of adding another gain stage to one channel for more drive.
     
  7. mc5nrg

    mc5nrg Supporting Member

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    You already have a schematic, but this site may be of interest:
    www.univox.org
    maybe you can sned them the scematic if they don't have it.
     

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