12AX7WA - TUBE AMP DOCTOR
VERY LOW NOISE, SOFT HIGH, AND EDGY WITH DOMINANT MIDS
Very low noise but slightly less gain than a regular 12AX7. ...

Tube Amp Doctor Ez81/6Ca4 Premium Tube Marshall 1974X
EZ81/6CA4 PREMIUM SELECTED – TUBE AMP DOCTOR
COMPACT SIZE FOR USE IN SMALLER AMPS
The TAD EZ81/6CA4 is a small rectifier tube for 6.3V filaments. It is used in smaller amps, such as the Marshall 1974X, the TAD 18W Plexi Kit, Silvertone amps and in various Hammond organ amplifiers. The TAD EZ81/6CA4 is a true full power EZ81. Also used in many audio amps and in those unbelievably good sounding old tube radios.