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Topic: Is this normal behavior for an old tone pot? |
James Detloff
From:
Minnesota, USA
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Posted 1 Jul 2012 4:34 pm |
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Hi friends!
The tone pot on my '49 Gibson BR-9 is acting a bit odd...I think! It seems to function perfectly well throughout its range. However...when I'm completely counter clockwise...and I mean nailed that direction...the tone seems to jump back to an area that sounds to me a little like about 1/2 way back up the travel. Could this be an indication of a failing tone cap (yes...its original too!) or should I be thinking about replacing the pot? Thanks!
---Jim |
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Stephen Cowell
From:
Round Rock, Texas, USA
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Posted 1 Jul 2012 6:09 pm
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My vote is for the pot... you can use an ohmmeter to verify the bad pot.
I have an old, bad cap on my T8 Stringmaster... it causes the volume as well as the treble to decrease, which would make sense if the cap is leaky, as I suspect. |
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Steve Ahola
From:
Concord, California
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Posted 1 Jul 2012 6:37 pm Re: Is this normal behavior for an old tone pot?
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| James Detloff wrote: |
| ...should I be thinking about replacing the pot? |
I have a 1949 Gibson Century 6 and the pots on that needed cleaning. Unlike the pots you usually see today there was no "window" by the terminals to spray in spray cleaner (DeOxit Red for cleaning, DeOxit Gold for conditioning).
There are 4 tabs holding the back onto the pot and after bending them out you can lift the back up enough to spray the resistive path. Be careful not to rotate the pot shaft too much because you don't want to get it on the wrong side of the "bump." I usually use the DeOxit Red to remove any crap built up and the Gold to condition the contacts to help prevent crap from building up in the future. (BTW I will treat all of the new pots I use with DeOxit Gold- I think it makes them work much better.)
If the shaft does not turn smoothly in the brass bushing add a few drops of a very light oil (like sewing machine oil.) Sometimes just adding the oil to the bushing to fix a deep spot on a pot but I like to clean it with DeOxit as well.
What is interesting about a tone pot is that when it doesn't make a good contact at some point when rotating it the sound will get louder and brighter (with a volume pot the sound will cut out or at least get softer.)
Steve Ahola
P.S. Whenever you do replace old pots be sure to save them. It is not just a vintage thing- in many cases the taper is much better than a replacement pot and unless someone really ground down on the pot they do last a long time.
_________________
www.blueguitar.org
Recordings on electric guitar:
http://www.box.net/blue-diamonds
http://www.box.net/the-culprits |
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James Detloff
From:
Minnesota, USA
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Posted 2 Jul 2012 12:51 pm Re: Is this normal behavior for an old tone pot?
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| Steve Ahola wrote: |
| James Detloff wrote: |
| ...should I be thinking about replacing the pot? |
I have a 1949 Gibson Century 6 and the pots on that needed cleaning. Unlike the pots you usually see today there was no "window" by the terminals to spray in spray cleaner (DeOxit Red for cleaning, DeOxit Gold for conditioning).
There are 4 tabs holding the back onto the pot and after bending them out you can lift the back up enough to spray the resistive path. Be careful not to rotate the pot shaft too much because you don't want to get it on the wrong side of the "bump." I usually use the DeOxit Red to remove any crap built up and the Gold to condition the contacts to help prevent crap from building up in the future. (BTW I will treat all of the new pots I use with DeOxit Gold- I think it makes them work much better.)
If the shaft does not turn smoothly in the brass bushing add a few drops of a very light oil (like sewing machine oil.) Sometimes just adding the oil to the bushing to fix a deep spot on a pot but I like to clean it with DeOxit as well.
What is interesting about a tone pot is that when it doesn't make a good contact at some point when rotating it the sound will get louder and brighter (with a volume pot the sound will cut out or at least get softer.)
Steve Ahola
P.S. Whenever you do replace old pots be sure to save them. It is not just a vintage thing- in many cases the taper is much better than a replacement pot and unless someone really ground down on the pot they do last a long time. |
Thanks Steve! I'll probably bring it in to have the pots cleaned and lubricated. I'd hate to ruin the originals!!  |
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Billy Tonnesen
From:
R.I.P., Buena Park, California
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Posted 2 Jul 2012 8:53 pm
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Pots eventually wear out and have to be replaced, especially the one in your foot volume control. Even the one on the Guitar will eventually get some kind of dirt in it and will start to fail. In later l years they started sealing the Pots to keep dirt out so they would last longer. Your Guitar could very well sound better with new Pots.
_________________
Sacramento Western Swing Society Hall of Fame, 1992 |
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Steve Ahola
From:
Concord, California
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Posted 2 Jul 2012 10:05 pm
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| Billy Tonnesen wrote: |
| Pots eventually wear out and have to be replaced, especially the one in your foot volume control. Even the one on the Guitar will eventually get some kind of dirt in it and will start to fail. |
I agree that dirt will get in the foot volume pedals. Inside the sealed control compartment of a guitar I think that a bigger problem over time is the corrosion of the resistive path and the wiper. As long as the corrosion is dealt with in a timely manner it can often be cleaned up. But as you say once the crap has been ground into the pot elements it can trash them.
I am a retired repairman (heating, air conditioning, appliances) so it is natural for me to want to fix things. However if James is going to pay someone to clean the pots I agree with you that it might be better for him to just have them replaced.
Steve Ahola
P.S. I was just thinking thinking that because you are a long-time pro you probably run into a lot more worn-out pots, Billy. I think that a lot of the old lap steels around today spent most of their life in attics, garages and basements where corrosion can be a big problem. I believe that the BR-9 was the biggest selling lap steel model for Gibson- maybe even the biggest selling lap steel model from all mfgs. I just looked in my own pre-50's BR-9 and the pots have no opening- they are not hermetically sealed so moisture etc. can get in.
_________________
www.blueguitar.org
Recordings on electric guitar:
http://www.box.net/blue-diamonds
http://www.box.net/the-culprits |
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