Mark V Combo gain controls in channels 1 and 2 cause crackling/hissing noise when rotated

[user 85400]

I have a Mark V combo, purchased 2011 and kept unused for the last few years, Today, after putting the amp in standby to warm up and then turning on to play I notice that in channels 1 and 2 (but not 3) when I turn the gain control clockwise or anticlockwise, there is a pretty noticeable crackling noise or white noise that is triggered by the turning of the control and ceases immediately when the control is not turned. This noise is independent of what other toggles are in use in those channels. Only the gain control is affected and only in channels 1 and 2, which makes me think that it is not tube-related but I am not sure how I would verify that assumption. Might the noise be caused by dirt or corrosion on the pot control? Can I access that pot and clean it with a suitable agent or cloth?
I would be grateful for any advice or suggestions, pointers to other threads that I may have overlooked.
Thanks in advance!

 

[tbonesullivan]

Definitely sounds like dirty pots. Was it kept covered? You'd be amazed how dust can get inside things over time.
Cleaning the pots normally isn't hard, but inside a Mark V 90, getting access can be a PITA.

 

[Elliot Twist]

Try turning ALL the knobs from zero to ten about 50 times each. (on every amp you own).
I'd suggest doing it at least twice a year. I some times use a flat shoelace on the knob to make it happen.
You're lucky the sound was only "a pretty noticeable crackling noise or white noise" and that you weren't at a gig and the sound cut completely out at the sweet spot you wished for.
I don't change the knobs on my amps once they're perfect for me.
Smartphone pictures of the knobs is a great tool. Thank goodness I lived into the future.

 

[user 85400]

Try turning ALL the knobs from zero to ten about 50 times each. (on every amp you own).
I'd suggest doing it at least twice a year. I some times use a flat shoelace on the knob to make it happen.
You're lucky the sound was only "a pretty noticeable crackling noise or white noise" and that you weren't at a gig and the sound cut completely out at the sweet spot you wished for.
I don't change the knobs on my amps once they're perfect for me.
Smartphone pictures of the knobs is a great tool. Thank goodness I lived into the future.

Thanks Elliot, very helpful advice. I have rotated gain and master knobs on all three channels a lot in the last playing session with the amp, and the situation has certainly improved. Probably really just a matter of the amp having not been used for a number of years and stored in the cellar where there is inevitably a certain amount of dust and dampness which could affect the amp's inner parts, although it was always covered. It seems that it really is a case of using the amp regularly to keep it in good condition.

 

[user 85400]

Definitely sounds like dirty pots. Was it kept covered? You'd be amazed how dust can get inside things over time.
Cleaning the pots normally isn't hard, but inside a Mark V 90, getting access can be a PITA.

Thanks, the situation has improved just by rotating the affected channel knobs clockwise and counterclockwise a number of times, and they are more or less now pretty silent when just being turned, even on the 90W setting. Although the amp was stored in its cover it was in the cellar where dust and dampness are of course an issue.

 

[tbonesullivan]

Try turning ALL the knobs from zero to ten about 50 times each. (on every amp you own).
I'd suggest doing it at least twice a year. I some times use a flat shoelace on the knob to make it happen.
You're lucky the sound was only "a pretty noticeable crackling noise or white noise" and that you weren't at a gig and the sound cut completely out at the sweet spot you wished for.
I don't change the knobs on my amps once they're perfect for me.
Smartphone pictures of the knobs is a great tool. Thank goodness I lived into the future.

I'm not an expert, but if there is dust and oxidation on the tracks, rubbing the wiper back and forth without cleaning / lubricating it sounds like it might have a detrimental effect on the service life of the pots.

 

[79fwlthree]

I use deoxit. There are 3 grades, red, gold and green. Get it from Amazon. If you are worried about the insides, use the Green. It is safer for plastics. Just remove the knob and squirt a little bit on the shaft and work it back and forth. It helps to have the shaft vertical so it runs down into the pot quicker. I have 40+ amps and I live in South Florida, so this is a necessity on a routine basis. Got this from my Keyboardist neighbor who used to own a repair shop in PA and it works every time.