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12AX7 is a miniature high-mu (AKA high gain and high transconductance) twin triode. Each triode section has separate cathode connections. 12AX7 was originally introduced in 1947 by RCA and was originally intended for voltage amplifier, phase inverter and multi-vibrator or oscillator application. After almost 60 years, 12AX7 still sees wide use in guitar amplifiers, audio amplifiers and ever growing list of recording equipments.

Current Production:

12AX7 equivalent tubes are being produced at Reflektor, Ei, JJ and Chinese factories today. Current production 12AX7 on market today are:

  • Sovtek 12AX7LPS
  • Sovtek 12AX7WA
  • Sovtek 12AX7WB
  • Sovtek 12AX7WC
  • TungSol 12AX7 Russian-Issue
  • Electro-Harmonix 12AX7EH
  • Electro-Harmonix 12AX7EH Gold
  • Shuguang 12Ax7C9
  • EI 12AX7 Silver Bullet
  • EI 12AX7 Elite Gold

Plug compatible variations

  • 12AX7A/7025 - Lower filament hum
  • ECC83 - European Version
  • B339 - Marconi/GEC version
  • 6EU7 - 6.3V filament version originally by GE
  • 12AD7 - Fatter filament with lower hum
  • 20EZ7 - Series filament 100mA
  • 5751 - Aircraft/military and computer application
  • 5751WA, 12AX7WA - Vibration resistant version of applicable types
  • 6681, 7058, 7729 - Higher reliability mobile applications
  • 6851 - Bendix aero space version of 5751
  • 6057 - Brimar high reliability
  • E83CC - Philips/Siemens Special Quality version
  • ECC803S - Frame grid lower microphonic version
  • M8137 - Long plate version by Mullard
  • CV492, CV4004(M8137), CV4017(5751), CV8156, CV8222, CV8312, CV10319 - Various British CV versions

Other variations of 12AX7:

  • 6AV6 - Has one unit of 12AX7 with diodes
  • 6DR4 - Half of 12AX7
  • 6BK11, 6K11, 6Q11 - Compactron versions
  • 6C10 - 3 x halves of 12AX7
  • 5755/WE420A - Very low frequency/DC amplification version by WE and others. Super low microphony.
  • ECC83M - 6.3V only version with shield like 6DJ8
  • 6CC41 - Variation by Tesla
  • 6N2P - Russian copy
  • 12AK7 - 12.6V only version by TungSol
  • ECC808 - Valvo super quiet version with filament and grid shields. Often found in vintage Telefunken equipment
  • E283CC - With shields like ECC808, frame grid like ECC803S The ultimate low noise 12AX7

Source: BOI Audio Works

Material herein added and updated constantly; presented for inspirational and educational purposes per Fair Use.

Last modified 19 Sep 2017

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