[quote name='Dad3353' timestamp='1443057150' post='2871902']
For bass, I'm looking for clean headroom. My Hiwatt 200w valve amp, with 4 x KT88s, does this. A less powerful valve amp, or most guitar valve amps, won't do this (I tried a Peavey guitar head once; I'll not do that again...). To get clean valve headroom, a couple of EL84s won't do it, so what works for an AC30 doesn't work for bass, or at least, the clean tone I want from an amp. SS amps can do the job, but only if we 'up' the power rating, and thus more expensive cabs able to handle the watts. Typically, a guitarist will be looking, in an all-valve amp, to 'bend' the o/p stage valves. For bass, I don't want this at all. The price to pay is big bottles, with big transformers, which means heavy and expensive. So be it. I could have chosen to play the harmonica.
Subject to completion, correction and/or contradiction from others.
[/quote]
This.
Bass is power. Powerful valve amps are heavy and expensive because valves are not efficient, (and as already stated) there's low demand and they're expensive to mass produce for that demand.
100-200w amps are around and reasonable cost. Think Fender Bassman (135w), Mesa Boogie Buster combo (200w), Marshall Superbass (100w), Matamp if you can find them, Soundcity heads (120-200w). Above that, Mesa Boogie Bass 400+ heads are fantastic and can be had for between £600-1000 depending on whether you import from the US or not. Otherwise you won't get much change from £1200.
Besides which, unless someone is playing large venues, the low end from valve heads tends to be overwhelming for small venues...in my experience at least.