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I've got a King brass sousaphone that seems to play sharp. I can't seem to correct it with the tuning slides. Is this common with Kings? Any suggestions to help correct it? It needs a cleaning. I'm looking for someone to do that now. I'm hoping that helps. Was thinking the problem might be me but I also play a King tuba and it doesn't have this problem at all. The tuba does, however, have an additional tuning slide that I have pulled out a little.

It was supposedly stored under a high school stage for 30 years or so. There could be a number of things in there.

I once found a dead mouse in the main tuning slide tubing an old Buescher helicon; it was formed into a perfect rod-shape, just like a fuzzy cigar.....

How about the tuning bits at the mouthpiece end? (Usually needs 2.) A smaller shank MP just may insert too far thus raising the pitch. It just may be possible that someone swapped out the main tuning slide with another King tuba or sousaphone/recording bass. I have had experiences where the legs or ferules on the tuning slide were longer or shorter than others. Not sure why. Someone here once mentioned tuning differences when using a recording bell over the upright bell and the need for a short and long tuning slide. I'm almost certain King used the same bore tuning slide on both tubas and sousas but the length of the slide could vary. Its possible a shorter slide may have found its way into that sousaphone. Just some ideas. Yes, an obstruction at a critical place inside the horn, could retune the horn much the same as the hand inside the bell of a French horn.

Let's hope thereare no mice in there. Just dropped it of to a local guy I'd been trying to get ahold of. He said there is a 4th slide on there that is stuck. When I bought the horn I as told there were 3 slides and they all worked. He said the one that's stuck is the main tuning slide. He thought that should fix the problem.

Thanks for all the responses. Turns out there are 7 movable slides on my horn and 4 were stuck. One of them was the main tuning slide. There was also a massive leak and 40 years of funk in the horn. Got it fixed and cleaned. Plays great now. The horn seems to play right in tune (or as close as I can get it) and it seems louder. My wife's won't be happy about the louder part.