ECC83, 12AX7, E83CC, E803CC, ECC803(S), 12AX7WA, CV4004, 7025, B759, 6681, 7242, 7729, E283CC, ECC808, 6KX8, B339, 6932, M8137

Versions the ECC83/12AX7 comes in are:

* ECC83/12AX7, ECC83 and 12AX7 are exactly the same, 12AX7 is the USA name and ECC83 is the name used in Europe. The ECC83 can be found in 14mm (normal) and 17 mm plate versions. The 17 mm are preferred by Audiophiles. The 14 mm version made by Mullard sometime have the box-plates. The 17 mm versions can have ribbed and smooth plates. The ECC83/12AX7 can only be used in parallel heater applications.
 

* The CV492 is a special version of the ECC83 made by many manufacturers. This tube is often referred to as the best sounding tube.
 

* 12AX7A is the same as the ECC83/12AX7, except they can also be used in series heater applications
 

* The 7025 is the low noise industrial version. It has spiral wounded heater wires to reduce hum and noise. These can be used very well in high-demanding audio applications.
 

* The E83CC or 12AX7WA, 6681 and the English special versions CV4004, M8137, 6932, 7242 and 6057 are premium military and industrial versions of the ECC83/12AX7. These tubes are made for long life and can withstand a lot of on/off cycles. They also are extra ruggedised and sometime have triple mica.

The 6057T is a special quality version of the 6057 made by Brimar in the UK.
 

* The B759 is a ultra-low noise version of the 12AX7, with matched triode elements. These types were only made in England by Genalex (Marconi-Osram Valve Co.)
 

* The 5751 is the "mil-spec" version of the 12AX7. It has slightly lower gain than the ECC83 (70 against 100), but this also reduces hum and noise. The 5751 comes in many versions. There are black plates, double and triple mica version and some have extra support rods. The triple mica version have three mica support layers and this reduces microphonics.
 

* 7729 is the premium instrument grade tube made only by CBS/Hytron. This tube has heavily plated gold pins.
 

* CV4035 is a flying leads very special quality version of the ECC83. Most problems arise in the pin/socket connection, so this tube is made to be soldered directly into the circuit. Also internal it is made to highest low noise and microphonics specifications, very special tube!
 

* ECC803(S) is the premium version of the European ECC83. These tubes were made and tested for low microphonics and low noise. The "S"-version is specially selected for low noise.
 

* The E283CC is a very special quality ECC83/12AX7. As good a sound as the famous ECC803S made by Telefunken, it also has a frame grid. It has different pin out (shielding between both sections), but is electrically equal. It is easy and worthwhile to make the modification!
 

* The ECC808/6KX8 is a very low noise ECC83/12AX7 replacement. It has different pin-out (symmetrical build up and shielding between both sections), and has lower maximum plate dissipation (0.5W against 1W). When you need very low noise and high channel rejection, this type is the best choice.
 

* 6H2pi, Russian near equivalent of the 12AX7 / ECC83. It has almost the same pin-out, but has 6.3 V heating on pins 4 and 5. Pin 9 is connected to a shield between both triodes. The 6H2n has slightly higher gm then the 12AX7 / ECC83, giving it more power and authority than the 12AX7 / ECC83. Great tube for replacements.