Finally got around to doing a shoot out with a bunch of tubes in the AKG.
Extremely time consuming, given warm up times and change over time etc..
Tip: Remove the rubber yoke until such time as you're done swapping. Saves a bit of time & tinkering.
Anyway, the results. (entirely subjective) The JAN Phillips 12AX7WA, which I think is actually the original valve, beat everything
hands down with the exception of the Telefunken ECC801S/12AT7 which in itself is an absolutely fantabulous vacuum tube.
Much hyped and selling for as much as $125 apiece on E-bay but an absolute winner nonetheless.
The Mullard 12AT7 tubes were a bit dark to my liking and the JAN Phillips, given that it is a 12AX7 thus requiring less gain,
was much brighter in comparison.
I thought for that reason,(12AX7 vs 12AT7) the Philips would beat out the Telefunken but it didn't. At least, not to my ear.
The Telefunken was fairly even and true to the sound across the whole spectrum whereas the Philips kind of morphed into
a very warm, bassy rumble at the extreme lows and a real vintage, ribbon like sound in the highs.
I could have gone with either but I'm keeping the Telefunken in the mic and will find a safe way to store the Phillips in the case
since both are excellent tubes and in my opinion, well suited to the mic.