Differences between 6922 and 12AU7?

12AU7 is a high-gain tube very often used in power amplifiers as the driving one. It's also dual-triode that can be used in differential inverting connection just like OPAmp.

6922 is also dual triode has a lower gain than 12AU7 but used for the same purposes where large isn't neccessary i.e. in preamps.

Could be the other way arround but I guess that mainly 6922 is used in preamplifiers

Then there is the fact that the 12AU7 is a 12 volt filament while the 6922 runs on 6 volts.

6922-6DJ8 indrustral a frame grid tube used origionaly for UHF the tube was never design for audio use some like the plate curves since the are pretty even.
There is no magic to this tube as some think and as I remember it has a higher gain than a 12AU7.
The pin out is also differant a 12AU7 can be wired to run 12V as well as 6V heater as for 6922 will run 6V only.
12AU7 base diagram is 9A which 6922-6DJ8 is 9LP in the GE tube book.
It all depends on the circuit requirement of the amp what tube is suited.