these are your options, instead of just rolling with the same tube number,
you can also try other numbers from different brands....
the 12au7 is a long-tail pair phase splitter, also called a differential amplifier, it can be replaced with a 12bh7, 12ay7, the 12ax7 voltage amp can be replaced with a 7025, 5751, 6201, 12at7, 12az7, 12bz7......