IMO the Mullards are hard to beat. Telefunken are also quite good and I agree w/ Reynolds853 in regards to neutrality.
Brimar/Amperex bugleboy have been good for me also but it's been a while since I've used them and memory can't always be relied upon...
This may be anathema but Groove tubes has a spiral filament
12ax7 that is supposed to emulate the Mullard, but I have only used them in a guitar amp. (Old Marshall- that originally came w/ cv series Mullards- I took them out so I didn't wear them out) The Groove tubes are a great substitute in that application and I really don't think the character of the amp changed much if any- I was smiling the entire time I played it which was true with the Mullard preamp tubes as well :)
Brimar/Amperex bugleboy have been good for me also but it's been a while since I've used them and memory can't always be relied upon...
This may be anathema but Groove tubes has a spiral filament
12ax7 that is supposed to emulate the Mullard, but I have only used them in a guitar amp. (Old Marshall- that originally came w/ cv series Mullards- I took them out so I didn't wear them out) The Groove tubes are a great substitute in that application and I really don't think the character of the amp changed much if any- I was smiling the entire time I played it which was true with the Mullard preamp tubes as well :)