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I am doing consulting and teaching work at a local high school. One of the Miraphone 186 tubas plays considerably flat. Pitch on the "F" just below the staff is even flatter than the Bb below the staff and also second line Bb. I have checked for leaks and valve alignment. The horn plays better in tune with a mouthpiece that has had the shank shortened (cut) by about one-quarter to one- third inch in length. I have also noticed that using this mouthpiece has no negative affect on the overtone series. Two questions: (1) Has anyone else experienced this problem? and (2) Are there other solutions to consider? Thanks in advance for your thoughts.

Hard to tell without more information or actually having a disinterested player try the horn. That being said, with the low BBb, F and Bb being flat it seems as though the horn itself is a bit low. If the entire horn is low and the slides are the normal length, there is a good chance the fingered notes will land in tune or close. I have always found that on Miraphones that all the tuning slides need to be pulled out and then occasionally pushed to adjust tuning on the fly. If you are trying to play the horn with them all in, tuning will be off, most noticably when playing scales.

Back to the shortened MP. A shortened shank can have some subtle intonation effects. Vis a vis the Monette line. But if you are simply cutting the shank a bit, the insertion point is still the same with regard to the throat of the MP. But what is happening is some alteration of the end of the mp and the venturi where the lead pipe begins to expand. Some refer to this generically as the "gap." This should really effect slotting and response more than anything.

Some mouthpieces work better than others on some horns. I have a few experimental prototypes that through off the overtone series noticeably. They are really too deep and to big of a throat.

Depending on the age of the Miraphone/Mirafone, some of those made back in the 1960s had leadpipe issues that threw off the horn's response, intonation and slotting. Players I knew at the time had replacement leadpipes installed and the problem was solved. Bob Palanshe from the Army Band did the surgery. Miraphone eventually made good and corrected whatever that problem was.

I know my next example is not about Miraphone, but rather some of the East German/Soviet Block horns that were very flat, being tuned to something around A = 439. (European low pitch.) We had three in college and I recall that taking the hacksaw to the main slide was the remedy. Drastic and permanent, but effective.

Usually for the harmonic series to be off considerably, there needs to be some significant compromise to the lead pipe or even more drastic problems in the main bugle. Yes, leaks and miss alligned valves can cause issues, as can lumps of solder (or dead creatures) that have formed inside the tubing.

Often students (and even adults) have quirky embouchures that over adjust between registers and wind up playing much flatter in the low and sharp in the mid to high. That is why I suggested getting a third party, preferably a competent pro, to give it a blow.

There are also nodes and antinodes along the lenght of the horn that are more reactive to damage, and some that seem to not have any sensitivity to the accoustics of the horn. I have a CC BAT that plays identically the same with the water key open or closed. Were it in a different place, I imagine the results would be much different.

So, playing detective or forensic repair tech seems to be in order.
The old addage (if nothing changes, then nothing changes) tells me that something will eventually be found that can correct the issues and make it play like a 'healthy' Miraphone. Good luck and I am interested in what others might have to say, that are much more experienced than I.

Paul "who in another life would have loved to have been a forensic scientist" Maybery

I'm glad I wasn't the only player experiencing the flat 60's mirafones. Thanks for sharing Paul Mayberry.