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Marantz 7C noise


JMCMAN

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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.

thank you

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11 hours ago, JMCMAN said:

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.

thank you


I am not sure what you mean by stray voltages.  Has it been professionally restored?

 

The first thing I would do is remove the tubes, treat the pins with Deoxit, and re-insert.  The sound you heard is oscillation.

 

Maynard

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Stray voltage= 0.35 ac volts measured on main preamp out to amplifier

the voltage will change if I lower the bass tone control to 0.1 ac volts, likewise if I use the high or low filter a slight variation in voltage.

the preamp is close to original the only changes were a new rectifier and volume control.

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