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 NEW  Bruce Heran outlines the details and construction of his simple DIY 6DJ8 (ECC88) Tube Hi-Fi Headphone Amplifier Project.

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 Post subject: knobs
PostPosted: 31 Jan 2012, 10:50 
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Joined: 31 Jan 2012, 10:39
Posts: 2
Hey. I joined this site because I just bought a stereo cabinet circa 1960's and I'm having problems with the knobs. It's a huge Zenith, model MM2640, and pretty much everything works except the volume, treble/bass, and balance knobs. They don't give consistent results when adjusted and jump all over the place. Does anyone know of a quick fix for this? The thing seems to have barely been used by the original owner, the manual is still inside. I'm imagining there's corrosion in there that's interfering. I took apart a rectifier we used for plating at work because the knob was giving us similar problems and it was just a matter of using a fine grit sandpaper to clean the contacts. The cabinet doen't allow easy access to get at the knobs, though. Any suggestions would be greatly appreciated.


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 Post subject: Re: knobs
PostPosted: 31 Jan 2012, 18:19 
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Joined: 04 Oct 2008, 11:29
Posts: 375
Location: Chillicothe, Ohio
Sounds like the problem is crud in the individual potentiometers, and not the knobs. This is very common in older gear, whether it's been used or not. In fact, lack of use probably makes the problem worse. The best fix, if dirt is the issue, is to spray some Caig Deoxit into the contacts of each control, then work them back and forth. There is quite a lineup of Deoxit products, and one of them would be ideal for this. I usually get mine at Parts Express. If the potentiometers are bad, that's another problem entirely.

Cheers,
Greg


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 Post subject: Re: knobs
PostPosted: 31 Jan 2012, 18:32 
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Joined: 31 Jan 2012, 10:39
Posts: 2
Thanks for the tip. I tried using some Plasticlean which we use at the shop to clean quartz watch movements but that product you mention might work better. I'll check out Parts Express. Would the potentiometers go bad from age alone? What's the best way to get it into the potentiometer? Can I just pull the knob off and spray it down the stem?


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 Post subject: Re: knobs
PostPosted: 31 Jan 2012, 19:19 
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Joined: 04 Oct 2008, 11:29
Posts: 375
Location: Chillicothe, Ohio
Most of those ancient pots have some openings in the back. If it's an old console stereo, it shouldn't be all that difficult to access the back of the unit. Maybe remove some kind of panel on the back. I'd get someone to help by spinning the pots while you spray Deoxit. Even if you can't clean them, use over time may be of help.

Cheers,
Greg


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 Post subject: Re: knobs
PostPosted: 02 Feb 2012, 19:42 
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Joined: 11 Oct 2011, 19:39
Posts: 180
Deoxit works VERY well. Get a can and try it for yourself. You will see a marked improvement in your pots. IMHO, it works far better than the old contact cleaner that radio shack used to sell.


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