Yes I know that Craig has proposed the AD1 tube use at the beginning but later discontinued.
Was it because of the socket used? because the AD1 use europasocket which is quite different that the
UX4 socket. I have the AD1/UX4 adapter DIY made so that I can use the AD1 tubes with the BA right now
and so far there is no problem. It has more beautiful mid, very organic mid, very transparent and clean sounding,
heads above the rest. However I don't know whether the PX25 modded will provide the AD1 tube use
at their optimal level. BTW I use the TFK AD1 NOS with barium pill, Tungram AD1 and Philips 4683