The 12AX7 high impedance amplifier triode was designed specifically for audio use and has a high amplification factor of 100. This is an American design that was copied by many other companies.
The original 'W' suffix denoted a rugged version designed for use under conditions of vibration and featured double mica sheets.
The retailer's Groove Tubes logo.
The double mica sheets are seen clearly in this image. Also the anode box is larger than the original 12AX7 giving a greater grid to anode spacing. Between the triode sections is a screen plate that does not appear to be connected to the outside world.
The central screen and on the right triode the heater can be seen emerging from the cathode.
The thin glass tube envelope is 22 mm in diameter, and excluding the B9A base pins is 48 mm tall.