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Tony Kniffen in Indianapolis plays BBb frequently, if not exclusively, as his contrabass tuba. Gene Pokorny has been playing BBb occasionally; I believe that Norm Pearson does, too.

Ross Tolbert played BBb in the Minnesota Orchestra for many years.

I'm not sure about this, but I believe that Ev Gilmore played BBb in the Dallas Symphony.

James Jenkins plays BBb and F in the Jacksonville Symphony,
David Townsend also when he was with the Richmond Symphony.

Don Harry of the Buffalo Phil has played BBb on occasion.

Ev Gilmore (Dallas) and Ross Tolbert (Minneapolis) were both mainly BBb players. Not current, I know but it's a short list.

A few more from past:

Dan Heeren - Denver & sometimes CSO at Ravinia
Charlie Guse - Chicago Lyric Opera
Connie Weldon - Kansas City and Miami

All of above had King Monster 4 RV

Bob Bauchens - Chicago Lyric Opera a very large old Huttl 4RV

I believe there has been a player with Detroit who used the same (King)as his regular instrument.

there have been others but some have slipped from instant recall.

When I was studing with Jake, using my King he advised me not to worry about getting a CC as the King was probably as good as or better than anything then available. He had me get one for him which he planned to use in CSO at times as: 1 it had a far better bottom end than the Yorks (though the top end was not quite as solid) and 2 he could sound the same and feel just as at home (with 'slight' less comfort due to BBb fingerings) as with the Yorks.
Who knows, if Dan had not been desperate for a suitable quality instrument and talked Jake out of the King IT might have become one of the CSO treasures.

Jake did consider having it cut to get around the fingering issue but Carl Geyer advised that it would only ruin a beautiful instrument as there was not enough straight tubing.

I believe that Sam has used some of these to make his Gnagney CC's. The use of a modern 4P=1R valve set with a shorter lead pipe would almost eliminate that problem.
These were a .750 bore. Like the Yorks, they played like a 4/4 but could produce the quantity of sound to match a 6/4.

I used mine with the Chicago Brass Quintet, and played it with the Melbourne, and Tasmanian orchestras and won the Perth orchestra job using it with a MW 32 as my "small" horn here in Oz. I also did a fair amount of trad, recording, concert band, chamber orchestra (in USA) and brass band and military (Australian Army) bands and Australian Ballet in Oz. I even used it for a private audition for Dorati for an "upcoming" position which did not eventuate. He had absolutely no qualms about me using it in that orchestra.