JJ 12AY7 Preamp Tube
The JJ 12AY7 Preamp Tube is a medium gain pre-amplifying double triode.
The 12AY7 can often replace a 12AX7 in your amplifier and give you a rich, warm tone with lower gain of about 60% than a 12AX7.
These tubes were used in many Fender Tweed era amps.
Get the datasheet here.