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OLD 69ish SHOWMAN dirty Bass and Middle controls


 :
5/24/2000 4:00 AM
Mark Sisco
OLD 69ish SHOWMAN dirty Bass and Middle controls
I recently brought out an old 69-70 ish Showman amp  
and it is noisy when you adjust most of the controls. Should I replace the control pots or can  
they be cleaned? Thanks Mark S
 
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5/24/2000 3:43 PM
Peter S

You can usually just clean them......I use Cramolin or DeoxIT. Radio shack also sells a turner cleaner that works pretty well. Sometimes the noise on the pots is caused by DC showing up on the grid of the tubes. This is caused by leaky coupling caps. You should check all of your coupling caps for leakage and replace the ones that are defective.  
PS
 
5/26/2000 1:15 AM
Rick Erickson

quote:
"Sometimes the noise on the pots is caused by DC showing up on the grid of the tubes. This is caused by leaky coupling caps."
 
 
Noise in pots can be caused by leaky coupling caps but the source of this voltage is the plate of the previous stage. Leakage of this type is extremely rare in a bf or sf Fender. Most likely cleaning the pots will cure the problem. Sometimes a tube will have excessive voltage on its grid, which is directly coupled to the wiper of the Volume pot in a Fender amp. This voltage will cause the same scratch as voltage from a leaky cap as the pot is rotated. Clean the pots and check the tubes first. There will almost always be a slight amount of voltage on the grid and therefore a little scratch as the pot is turned but it shouldn't be excessive.  
RE
 
5/27/2000 6:39 AM
Bruce

I've found plenty of BF and SF Fenders with DC on the volume and treble pots from the 250pF ceramic treble cap leaking too.  
About 98% of the time the noise is simply dirty pots and a proper job of washing them out with Deoxit and a relube will cure most of the noise for many hours of use.  
 
Bruce
 
5/28/2000 1:32 AM
Peter S

Every Tesla ECC83 I've tried has DC on it's grid....not much, but just enough to make the pots noisy.  
PS
 

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