Crazy gain pot???

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hendrix1983
Posts: 16
Joined: Sat Dec 06, 2014 10:11 pm

Crazy gain pot???

Post by hendrix1983 »

Hey guys not a valve amp, but I'm having an issue with my 1986 marshall 5212 2x12 fifty spilt reverb combo.

Basically the gain pot does nothing until it gets to 3/4 of the way up then bam it all comes on at once.

Basically the pot only works in the last 1/4 of its range and it's super sensitive. Like the slightest tweak delivers a massive increase of gain...

My thoughts is that the pots screwed. Any other ideas? Replace or clean with contact cleaner?

Thanks guys
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Dr-Joned
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Location: The Great South, USA

Re: Crazy gain pot???

Post by Dr-Joned »

Either a bad pot or possibly it lost ground reference in one end.
I Think I Think Too Much !
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Leo_Gnardo
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Location: Dogpatch-on-Hudson

Re: Crazy gain pot???

Post by Leo_Gnardo »

Worth a shot of cleaner spritz, maybe some crud has grown in there that doesn't let the wiper hit the track until it's nearly full up. OR the wafer is split, your track discontinuous, you'll need a new pot.
down technical blind alleys . . .
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M Fowler
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Location: Walcott ND

Re: Crazy gain pot???

Post by M Fowler »

http://music-electronics-forum.com/t12338/

Replace the linear gain pot with audio pot.
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JMFahey
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Location: Buenos Aires - Argentina

Re: Crazy gain pot???

Post by JMFahey »

It's not a conventional gain/volume pot with one end grounded but a feedback+attenuation pot, with the center lug/wiper grounded.

Replace it with a fresh 22k (or 25k , it's the same) linear pot.
It might have a cracked wafer as suggested above or somebody might have replaced it with a larger value one, say 220k or anything above 50k.
That would also deliver all the gain in the last 10% of rotation.
hendrix1983
Posts: 16
Joined: Sat Dec 06, 2014 10:11 pm

Re: Crazy gain pot???

Post by hendrix1983 »

Thanks guys I have cleaned the pots with contact cleaner and put my multimeter across it and it seems to be reading a normal range, as in as you would expect a good pot to behave.... As the tree said to the lumber jack I'm stumped...
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