TubeNet

Are you asking about the 3+1 Besson F tubas from the 1950s and 1960s or the few prototype four valve front action compensating Fs from just a few years ago?

I used to own one of the 3+1 instruments.

Adding to the previous post -- the 3+1 configuration may be worth considering. The compensting 4 front valve horn has not received positive comments on the TubeNet.

hth,