Quick silly question about tubes - K4040 amp

Kits Audio Hi Fi Projects
1

Hello,

First, I love my K4040 amp…

I want to know if its possible to put a 12AX7 (5751) in place of the 12AU7?

Would there be issues with too much gain ? Will it harm the unit ?

I am unclear exactly what the 12AU7 serves as, can you clarify what it does, its purpose?

Thank you !!!

2

Sorry, we have no experience with this modification.
The 12AU7 serves as pre-amp in this circuit.