Hello Chad. The 6922 will not work at all, and the 5751 will probably operate in the circuit but I sincerely doubt it would sound right. There are many appropriate electrical subs for the 12at7 such as the 6060,6201,6679,7728 or nos euro tubes like the B152,m8162, ecc81. The american 12av7 and the 12az7 will also sub for the 12at7 in many circuits. cheers David
