Anyone has information if 12AU6 and 12AU7 are interchangeble in preamplifier ?
Absolutely not. Don't even try it. It can do damage.
I took another look, and it won't even fit the socket. The 12AU6 is only a 7 pin tube, the 12AU7 is a 9 pin. So we don't have to even worry about being too late letting you know.