We design our equipment to only use tubes that are in production. That makes life a lot easier :)
Additionally, as long as guitar amp manufacturers are using tubes, there will be a supply as they use far more tubes than home consumer audio! So 12AX7s, 12AU7s, 12AT7s, 6L6s, KT-88s and EL-34s should remain easy to find.
Additionally, as long as guitar amp manufacturers are using tubes, there will be a supply as they use far more tubes than home consumer audio! So 12AX7s, 12AU7s, 12AT7s, 6L6s, KT-88s and EL-34s should remain easy to find.