Whilst everyone knows that this amp uses 6 x 6L6GC power valves there is a lot of confusion about what preamp valves are used.
I like this quote from one of the forums where the guy actually spoke to Mesa:
“I spoke with George from Mesa Boogie today. He cleared things up for me on the D180 preamp configuration.
Apparently there are three versions… one had 2 12AX7’s in the preamp, a 12AT7 phase inverter and one more 12AX7 in the final master stage. A second version had one 12AX7, 2 x 12AT7’s and a final 12AX7. The last version had 4 12AX7’s.
The amps were only labeled if/when they had different tube sockets”.