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Scratchy Treble Pot Causing Volume Loss??

Bluesful

Silver Supporting Member
Messages
42,062
Hi All.

I have an old BF Princeton Reverb with a scratchy treble pot. The interesting thing is that I think that pot may be causing the amp to drop volume, sometimes down to basically nothing after a period of playing.

The treble pot is scratchy if you turn it up and down continuously (the normal scratchy pot crackling behaviour). You can however set it at certain points and the amp will function fine, but at other points you'll get minimal - to no sound at all. For example with the treble set at 5 the amp works fine, but with it set at 4 you might get nothing.

Even if the treble is set to a level where the amp will produce sound after about 15-20 minutes of playing the volume will suddenly drop to a whisper and will fluctuate up and down a little. Basically though there's not a lot of volume there. Is the scratchy treble pot causing the amp to lose its volume after playing it for 15-20 minutes or is that something else?

I'll obviously need to clean the treble pot with contact cleaner, but I'm wondering if you knowledgeable chaps will be able to advise if the volume drop off is related, or something else.
 
Messages
826
Yes, it can do that if the pot wiper is sometimes breaking contact with the track. Contact cleaner may fix it, but if not you would need a new pot.
 

pdf64

Member
Messages
8,135
Modern audio pots tend to have a rather different taper (10% or 15%) then the ~30% type that tended to be used for BF treb and vol.
You may find a linear taper works better for you.
 

zenas

Member
Messages
8,872
Contact cleaner is the wrong word you want pot or tuner clean that leaves a little lubrication behind. (otherwise the pot might stick) DeOxit makes one but I'm not sure of the name? I've been using Radio Shack Tuner Cleaner for years. When I finally use up the last of what I bought as the stores closed around me I'll start using the DeOxit stuf.
A leaky cap will also make a pot noisy but this does kinda sound more like a pot issue.
 

Bluesful

Silver Supporting Member
Messages
42,062
Contact cleaner is the wrong word you want pot or tuner clean that leaves a little lubrication behind. (otherwise the pot might stick) DeOxit makes one but I'm not sure of the name? I've been using Radio Shack Tuner Cleaner for years. When I finally use up the last of what I bought as the stores closed around me I'll start using the DeOxit stuf.
Looks like this is the stuff? I'll have to find an equivalent of that stuff here, as it looks like you can't ship these cans.

A leaky cap will also make a pot noisy but this does kinda sound more like a pot issue.
It could be a leaky cap as some of the originals are still in there. It had a look over by a tech 2 years ago and a few were changed, but some were left.
 

Jeff Gehring

Gold Supporting Member
Messages
6,797
Looks like there are plenty of Australian distributors for Caig chemicals. Can they not ship to you within Australia?
 

Bluesful

Silver Supporting Member
Messages
42,062
Looks like there are plenty of Australian distributors for Caig chemicals. Can they not ship to you within Australia?
Yeah, after a bit of Googling there's a few local electronics shops that stock that Deoxit product. So no need to have anything shipped.

Hopefully cleaning the pot will stop the volume issue.
 






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