Stock 1959 and 2203 amps run EL34 pentodes in the power section. The Jose mod set is voiced for EL34 — particularly the NFB-reduction mod, whose effect interacts with the power-tube character.
EL34 under reduced NFB: - Mid-forward, slightly compressed feel - "Spongy" on transients (some sag from the OT and choke being driven harder) - Easy to push into power-tube saturation at moderate volumes - Classic British rock voicing
6L6 (sometimes substituted, especially in modded combos): - Tighter low-end, less midrange bloom - Cleaner headroom, less power-amp distortion at the same volume - Closer to Fender / boutique character - Under Jose NFB reduction, the looseness applies to a tighter base voicing — different feel, more "grand piano" than "British rock"
The Jose canon is EL34. Substituting 6L6 changes the gestalt; players should consider the substitution as making a Jose-flavored amp rather than a Jose amp.
(JMIL doesn't model power-tube type explicitly — it's a preamp-focused lab. Power-tube swap is Tier 4 territory and read-only.)