12AX7 / ECC83 Tubes
Other names for a 12AX7 include ECC83 5751 12DW7 ECC83, ECC82, ECC81, ECC823, ECC832, CV4004
The 12AX7 commonly known as an ECC83 would have to be the most widely used tube in existence. They have been used to drive audio units for decades and for good reason. These tubes are the starting point for amplifying your sound. The 12AX7 range should really include the 12AU7 / ECC82 and the 12AT7 / ECC81 as they are a drop in replacement in most cases. The 12AU7 and 12AT7 have less gain than the 12AX7 tubes which comes in handy if you are trying to tame that amp.
In addition, the JJ range has a couple of nice hybrid tubes in the 12DW7 / ECC832 and now the ECC823.
The 12DW7 is essentially a half and half tube, the first half is a 12AU7 and the Second Half is a 12AX7. Great for the first stepping in dropping the gain at the V1 slot.
The ECC823 is the opposite of a 12DW7 with the 12AX7 at the first half and then a 12AU7 in the second half.