Moving on over to the right thread here…
If you plan on upgrading the tubes for the Tuba, I can highly recommend the NOS RCA 7189. Also, a more affordable option are the NOS Soviet Reflektor 6P14P-EV. Both are better than the stock Reissue Mullard EL84.
The RCA 7189 in particular sounds amazing on the Tuba. The sound is more 3D, better bass response and treble extension…just a much more linear sound.
I got those rca tubes in hazi talks about, and they are pretty dang sweet. I agree that the stock are a bit mid centric and not as balanced, I then threw in some Holland bugle boys and they were pretty sweet for treble and mid-range, but didn’t quite do what I wanted for bass (but I knew that going in). The RCA are well balanced and overall just a generally good upgrade without making many sacrifices imo. It balances out the sound, improves sweetness, a bit more natural and accurate presentation…
It sounds like NOS RCA 7189 tubes are one of the best options for the Tuba with at least 3 people praising them. Unfortunately availability is rather limited.
I’m not personally a big fan of the stock new production mullards in the Tuba, they don’t have a particularly wide soundstage and they lack bass.
I think there is a win in replacing them, Mine has EI tubes in it, RCA are probably fine, GE tubes are reasonably priced decent performers for EL84’s, as are Tunsgram.
I will probably go with the EI EL84 tubes since they seem to be in stock here.https://upscaleaudio.com/products/ei-6bq5-el84