Here are few links related to the subject:
Will Kimball, Professor of Trombone at Brigham Young University, maintains an alto trombone history timeline his website. He added this about the Drei Equali:
Added the entry below to the Alto Trombone History Timeline. It includes information from a firsthand witness about Beethoven’s Drei Equali, arguably one of the most important works in the history of the trombone. Among the noteworthy observations about the alto trombone is Glöggl’s note that, although his father’s collection included soprano and quart trombones, the instruments commonly used in Austria were alto, tenor, and bass trombones. Son of the Linz kapellmeister who commissioned the work, the younger Glöggl stayed in the music field, eventually becoming a music publisher in Vienna. His recollections were made specifically for publication in Thayer’s Life of Beethoven (for source, see Alto Trombone Bibliography).
1812—Linz, Austria: Beethoven writes his Drei Equale for 4 trombones, a work commissioned by Kappelmeister Glöggl of the Linz cathedral. Glöggl’s son, who later becomes a music publisher in Vienna, verifies that alto, tenor and bass are the instruments commonly in use, mentioning that in his father’s “collection of old instruments he had a soprano and a quart trombone, whereas only alto, tenor and bass trombones were commonly used.” He continues, “Beethoven wanted to hear an Aequale such as was played at funerals in Linz, and one afternoon when Beethoven was expected to dine with us, my father appointed three trombone players and had them play an Aequale as desired…” (Thayer 541).
Since we had already heard the Bellon last week, I decided to play a recent recording the Atlantic Brass Quintet mad of "Voices in da Fan", by our trumpeter Andrew Sorg. We recorded it on a CD with a new work for brass quintet and wind ensemble by Kevin Walczyk entitled Quintet Matinee with the UConn wind ensemble as part of the Sackler Prize.
This is Andrew's second brass quintet composition, the first being "Mental Disorders". If you are interested in hearing this piece, I've embedded a video of live performance by a student quintet from the Atlantic Brass Quintet Seminar below: