I attended a wedding yesterday where the guitar player had this seymour Duncan Convertible. It featured a knob on the front that allowed him to go from 5w up to 100w. The amp had 6 power tubes. Why isn't this in all amps??? Is this not the answer to getting tube distortion and clean head room for jazz/country out of the same amp? How practical would it be to add this feature to my deluxe reverb? Do more power tubes create more wattage? So I could switch between lower wattage for overdriven rock/blues and higher wattage for clean headroom for jazz and country music.

Thank You!
MARTY FRIEDMAN--"It’s a lot easier to be technical than it is stylized; it really is... But I think it’s a lot more rare to have someone who’s really got their own sound because that’s something you can’t practice."
Tubes create, or rather, dissipate wattage, but it's done as useless heat. The wattage you hear is made (or rather consumed) by the output transformer and the speakers. More tubes equals more current available to pass to the output transformer, hence more "power".

The Duncan Convertible has a unique way of reducing signal by using an extra "dummy" valve that uses bias to act as a variable shunt of signal. So it appears to be a bit of a weird extra master volume. I'm not sure how good of a design it is, but the fact that no other guitar amps that I'm aware of have used it before or since seems to say a lot.

If you're looking for that sort of attenuation of volume while preserving valve distortion, look into the London Power solution, or a simple attenuator. None are perfect solutions, so do your research.
Tastes like chicken, if chicken was a candy.
some options work better then others.

the london power is supposed to be pretty transparent.

why isn't power scaling available in all amps?

i dunno. i think less people would have a need for it then you think.
Jumping on dat gear sig train.
PRS Hollowbody II / BKP Warpigs
Strandberg OS6T / BKP Aftermath
Strandberg OS7 / Lace Poopsticks
Skervesen Raptor 7FF / BKP Warpigs
Skervesen Raptor 6 NTB / BKP Juggernauts
Hapas Sludge 7 FF / Hapas Leviathan
Anderson Baritom / Motorcity Nuke BKP Sinner Anderson H2+
Warmoth Baritone / BKP Piledriver
Ibanez Rg2120x / BKP Nailbomb

Blackstar ID:Core Beam