ok, been checking on the web for alternative tubes to the standard sovtek in this head, but not a lot there, so i thought i'd do a wee bit of messing meself with what i had around.
the amp was bridged into 2 SWR goliath II 4 x10's (standard PAS drivers), all eq's at 12 o'clock, limiter off, brite off.
basses were; custom MM, mahogany body, rosewood board, bartolini TCT 3 band active, duncan SMB-4a. Fender Jazz 64' reissue, alder body, custom shop pups, rosewood board. both strung with DR hi beam 105's.
the contenders are:
[list]
[*]standard sovtek 12AX7
[*]standard marshall 12AX7 (suspect it's a shuang yung or something)
[*]electro harmonix 12AX7EH
[*]50's vintage brimar 6060 (12AT7)
[*]tung sol 12AX7
[/list]
...and the results?
sovtek (stock tube) - loud, bright, but a little brittle
marshall - pretty much as above
electro harmonix - loud, smoother and brighter up top. lows more defined and tighter.
brimar - much more sedate (as expected from the lower gain tube), but warm and round with less output (jazz especially liked this one).
tung sol - as EH, but more so. the MM favoured this one especially.
winner? for me, definately the tung sol, without a doubt.
don't know if that fairly unscientific, subjective account is of any use to anyone, but hopefully it's a wee bit of a guide can see this and the 500 being fairly popular, so feel free to add to if you have any more, or even if you disagree entirely!