Bass Trombone, brief description
“The bass trombone is a slide trombone with two valves that are operated by the left thumb. The valves make it possible to lower the instrument’s pitch from Bb to F or D. The entire chromatic scale only becomes available thanks to the thumb valve (F tuning) and an additional third-valve (D tuning).”
Bass Trombone: Instrument Studies for Eyes and Ears — Jacobs School of Music
Instrument Studies for Eyes and Ears, by Don Freund, site designed by Reid Merzbacher