12AY7 / 6072
12AY7's will allow for a cleaner tone and a bigger sweep of the gain and volume controls on your amp. It's commonly used as the phase inverter in some hi-fi amps, Ampeg and Fender amps. 12AY7's have less gain than a 12AX7, 5751, and 12AT7, but more than a 12AU7.
For less gain, you can substitute with a 12AV7.
For more gain, you can substitute with a 12AT7, or a 5751.