This is a very rough guide from my experiences...
American valves, general electric and RCA...... Big clean sound, lots of bass and treble.
Britsh valves, Brimar and Mullard....... Soft and warm with great bass.
Euro valves, Valvo and Telefunken.....very neutral with balanced sound.
You can also change te gain...
Ecc83 = 100
Ecc81= 60
Ecc82= 20
These are very rough findings and are not complete as there are many other valves that can be used to change the gain and tone.
Hope this helps.