Posted by Klaus on April 19, 2002 at 15:16:16:
In Reply to: Re: Re: Re: An interesting tuba on auction site posted by Vince on April 19, 2002 at 13:31:17:
"Shouldn't a diverter valve only have three ports, an "in" and two switchable "outs?" "
That is the type we know from Conn 8D (that is really Kruspe-Horner) style French horn wraps. Where each of of the two "sides" have separate "shunts" with their respective lengths of valve tubing put in the middle of the main bugle. Some sort of parallel routing.
But double brasses also can have their two valve sets serially routed as in this tuba. With the "switch" only adding the necessary difference in main bugle length. That would allow for a gradual increase of bore through each valve. I have no knowledge whether this happens on the tuba in question.
If this instrument should be played in the style of a double French horn, then the player should keep the fingers off the BBb paddles while playing on the F side and vice versa.
The Bb/F combination in horns is well know, as is the triple horn in F/Bb/F. Engelbert Schmidt (if I remember right) takes the obvious consequence of the 1+3 and 1+2+3 fingerings being not so well in tune. He builds triple horns in Eb/Bb/F. With only a fourth between adjacent sides of the triple all 1+3 and 1+2+3 fingerings can be avoided except in the lowest end of the F horn range (and even there, if one accepts to use pedal notes from the Eb descant side).
One note that would be a problem on the Kruspe tuba would be C below the staff. The fingering would be 1+3 on the F side as well as on the BBb side (or really 4+5+7 on the latter side). Which would both tend sharp. A very slight flattening could happen if the 3+4+7 fingering would be used.
The B natural a semitone below would be best in tune if fingered 1+3+6.
I see no problem in the German tradition of F bass tubas and BBb contrabass tubas. That is until they are combined in one instrument. Double tubas in F/C or Eb/BBb would have been much easier to build with decent scales.
This posting might be very cryptical. I have done a lot of calculations years back before I chose between Eb comp and 5 valve F as my first real bass tuba, so I have a spreadsheet template, where I can compare various fingerings. I am fairly sure, that my points made above are correct. Whether they can be understood is quite another matter.