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Thread: need help with my Marantz 7C

  1. #1
    Junior Member
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    need help with my Marantz 7C

    I have a Marantz 7C preamp that recently made a sound like a car engine revving up. Quickly shut it down. After looking inside the preamp I noticed some stray voltage when using the high line input selected. When I switch to low line level it zero's out. Not sure where to look for bad resistors or capacitors or switch in that high line input circuit. Any help would be greatly appreciated.
    thanks

  2. #2
    Senior Member
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    Marantz 7C - 60+ years of service!

    Quote Originally Posted by Jimbo View Post
    I have a Marantz 7C preamp that recently made a sound like a car engine revving up. Quickly shut it down. After looking inside the preamp I noticed some stray voltage when using the high line input selected. When I switch to low line level it zero's out. Not sure where to look for bad resistors or capacitors or switch in that high line input circuit. Any help would be greatly appreciated.
    thanks
    Best wishes re all the above but may be wishful thinking. I purchased my 7C (7) in 1960 but as the decades rolled past it became increasingly difficult to keep in shape. Strange noises, internal grounding problems that I was unable to resolve. Replaced/cleaned all the various wipers/pots multiple times - the output pots had to be fabricated - no parts. Selenium power supply rectifier on the way out. A lot - most - of the caps in there are proprietary gold band. Nonetheless, all the socket voltages are in spec . . . but I have yet to figure it all out. Not an EE! Also, as you have observed, the chassis materials in there are are low grade, tin plated connectors, etc. 1950s. In any case, you're not alone. Great pre amp in its day.

  3. #3
    Member Fitero's Avatar
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    I would urge you to send it out for repair. A good tech will set it right.

    I bypassed the selenium rectifier and re-capped the power supply caps and some others out of spec in mine as a preventative maintenance procedure.

    Curiously enough, it took a couple hundred hours use after rebuilding for me to adapt to the new sound and hear the "magic" again.

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