Audio with sound off

I have a vintage Marantz 6300 TT I was having problems with maintaining a constant speed. The audio forums are full of others having the same problem. I took the TT to a local Dealer that has a great tech. He said the problem was a dirty Pot. I said I read many posts on audio forums where guys cleaned the pot and it did not solve their problem. The tech said sometimes it requires a deep cleaning of the pot. (There is one for 33 and one for 45)

It has been over two years now and the TT still holds a constant speed.

That was the first thing I tried. The volume control is very clean no resistance turning, glides so easy

You can't feel if it's dirty just by rotating it.

Pull the top cover and look to see if you can see the dual gang volume control pots. If not you might have to pull the bottom cover and see if you can see it from the bottom.

Sounds like a dirty volume control potentiometer.

With the preamp turned off.

You might try rotating it fairly fast back and forth several times through its' entire travel.

If that doesn't help you will have to clean it with a good contact cleaner. That is if you can get access to the dual pots on the back side of the face plate of the preamp.