Posted by Rick Denney on November 21, 2002 at 21:35:06:
In Reply to: Re: Strange Tuba posted by Collin on November 21, 2002 at 19:17:34:
A double tuba is similar to a double horn, in that it has a set of tubing devoted to one pitch, and a set of tubing devoted to another pitch.
A "full double" uses a switch valve in front of and behind the valves, both ganged on the same control, that switches the instrument through a second set of valve branches (the valves have two sets of ports on them) plus a little more open tubing. Double horns are full doubles, but the switch valves in front of and behind the three regular valves are part of a fourth double valve. This may not work for tubas. I've seen a picture of a York double tuba prototype that use two separate switch valves on the same linkage--the second one was well after the four regular valves and it was enormouse. Dr. Young's tuba is a full double that uses two separate sets of valves instead of one set each with two sets of ports and tubing.
A "compensating double" uses a switch valve to route the air back through a second set of valve ports and branches, so that the sum of the two branches on each valve work for the longer bugle. A compensated euphonium is really a compensating double of this type. When you press the fourth valve of a compensating euphonium, the air goes through the first three valves twice. With the fourth valve up, it's a Bb instrument, and with it down, it's an F instrument. But you don't play it that way, because all that valve tubing would sound stuffy. You just use the F side when you need it.
I believe the F/CC double tuba that was mentioned recently in response to the thread about Viennese F tubas is a full double, but I may be mistaken. Gronitz apparently still makes a full double on special order.
Rick "wishing he had a picture" Denney