#1
Got my first tube amp, 6505.
Five 12AX7 preamp tubes and four 6L6GC power amp tubes
If i ever need to replace these what ones do i get if i want the same ones? As so much different 12ax7... which gets me confused.
Could someone help?
I live in the UK so if someone knows a website in the uk that sells that would be great.
Cheers
Gear:

LTD MH250NT w/EMG's
Jackson DKMG
Peavey 6505 Head
Orange PPC412
Boss NS-2
#2
Any 12AX7 will function, but different types of 12AX7 will alter your sound
Alvarez dreadnought
Gibson SG
EC-1000
Homemade Strat (seymour duncan classic stack p/ups)
Vox Tonelab (original desktop model) with full board footswitch
Vox AD50
Avatar V30 4x12 cab
#3
I wouldn't worry about it for now unless you think you need new preamp tubes. Different brands of 12AX7s will sound different as mentioned. For example, Tung Sols are considered brighter and JJs are considered darker.

These two sites should help:

http://www.watfordvalves.com/and
http://www.hotroxuk.com/
Also try guitarguitar.co.uk.