A (set of) query(s) about Valve Amps

[SPHDS]

DISCLAIMER - I am posting this in multiple places, for maximum exposure/to get as many answers as possible, so sorry if you get fed up of reading it multiple times.....!)

Anyway......I was watching a video reviewing and comparing small valve amps (albeit guitar.....15/20W) , with a variety of speakers (10" and 12") and valves (types and quantities...ECC83's and 81's, EL34's, 84's and 6L6's, and anywhere between 2 and 6 tubes)
Now I know different valves give different sounds, and different arrangements of components used also influence characteristics....
So......during the review they described the amp with the most valves (6, 3 pre and 3 power) and least (2, 1/1), both same power, as 'lacking headroom' (which I get to mean that they were starting to distort with little provocation.....) So...what does the number of valves have to do with sound/character
Also two amps had exactly the same valves in the same configuration, wattage and speaker sizes......but did not sound that similar.....(both best sounding imho) Is the difference down to the other parts of the amp being different from each other?
And finally.....it is obvious that number of valves has little to do with wattage (most and least valves were both 15W, and 20W had 3 and 5 valves), so what determines power?

I am sorry if these are just stupid questions, I was just curious.....

[MWH]

Good questions, well asked !,  be interested to read any reply's from anyone with the right knowledge, but it would be long winded reply to cover it all 

[Snooder]

Hey, so in response (I think):

1) Valve amps use tubes on two separate sections on the circuit. You usually have your EC types in the pre-amp section and the your EL/6L6/KT etc are in the power section. Most your EQ type tones will be through the pre amp section, and in truth, the number of valves makes no difference to the sound here, rather the design of the circuit will be the biggest influence. Your power section is where you get the saturated "gain" tones on these types of amps. Your power section valves is where you get "break" up when you drive the signal hard enough through the pre amp. Once again, the number of tubes will only be dependent on the design and has no real baring on the tone.

2) Tonal character is defined by the type and even manufacturer of the actual tubes themselves as well as the circuit design. Also, quality of other components makes a huge difference, although some manufacturers swear by cheaper parts as valve amps are not meant to be "hi-fi"

3) Power is determined by your power output transformers. Usually the 2 giant metal lumps or torroidal transformers that you see (and feel) in valve heads. These get bigger as the wattage increases as they are what is required to "step up" the wattage.