Wagner's Heirs
The Wagner tuba's inclusion in the orchestra had its supporters in Heinrich Rietsch, Alfred Orel and Fritz Oeser but, even so, most composers didn't trust themselves to write for it. Humperdinck warned against its casual deployment and Mahler gave thought to using them but ultimately excluded them. Only a handful of post-Wagnerians actually composed for them:
Adalbert von Goldschmidt (1848-1906) in 'Heliantus' (1884); Jean Louis Nicode (1853-1919) in 'Das Meer' Op. 31 (1891); Friedrich Klose (1862-1942) - who had lessons with Bruckner - in 'Der Sonne-Geist' (1917); and Felix Draeseke (1835-1913) in 'Jubel-Ouverture' Op. 65 (1898)
in which Draeseke uses two B-flat tenor tubas & two basses in F, which are employed separately and in a jolly, galloping manner (a far cry from the hieratical tones of Wagner and Bruckner, a divergence for which he was rebuked by Richard Strauss). Left: Adalbert von Goldschmidt

Above: Goldschmidt's Heliantus