Posted by Numbers on May 30, 2003 at 10:56:01:
In Reply to: How to tell if HP or LP (helicon)? posted by Steven on May 30, 2003 at 09:02:26:
If the instrument is low-pitch, it's probably built for A=435, which means that about 2.6 inches would need to come off the total length for playing in A=440. Usually, this means about 1.3" from each leg of the tuning slide. Individual valve branches may or may not require a little trimming.
If the instrument is high-pitchs, it's probably built for around A=457, which means that about 8.6 inches of tubing need to be added to get it to A=440, usually by adding about 4.3 inches to each leg of the main tuning slide. On a helicon or sousaphone, this added length can get to be a problem, if the newly-lengthened slide now pokes the player in the ribs. Some manufacturers back around the turn of the century added an extra loop or dogleg to the tuning slide to adjust for the pitch difference, but it creates another problem in that water accumulating in the extra tubing is a pain to drain without pulling the slide and dumping the water. If invidual valve slides can be pulled out enough, one can leave them alone, otherwise, they'll need replacement or modification.
Smaller high-pitch instruments tend to do better when converted to modern pitch than the larger ones, which usually exhibit intonation problems after surgery. Small Eb tubas in generally usually survive surgery quite well. Low-pitch instruments generally do well after being converted to modern pitch, since we're only talking about 20 cents in tuning, not the 66 or cents of correction needed for a high-pitch instrument.
A good rule of thumb is that if the horn was made before 1900, it's probably high-pitch, as that was the prevalent US band practice at that time. Without a gooseneck or tuning bits, it'd be pretty difficult to make an accurate "eyeball" assessment.
Hope this helps,