Vacuum Tube Data Sheets

12AX7 / ECC83

Application notes


The tube can be used without special precautions against microphonic effect in amplifiers in which the input voltage is higher than 50 millivolts when the tube is mounted in the near vicinity of a 5 watt loud speaker with an acoustical efficiency of 5%.


The hum and noise level will be better than - 60 db when the grid circuit impedance is less than 0.5 megohms (at 60 cps), the center tap of the heater is grounded and the cathode resistor is decoupled by a capacitor of at least 100 uf.

12ax7 microphone amplifier schematic


Supply Voltage 250 350 volts
Cathode Resistance 1200 820 ohms
Total Current 1.08 1.70 mA
Output Voltage6 (RMS) 35 45 volts
Voltage Gain 58 62
Percent Distortion7 5.5 3.5 %

6 Eo at grid current starting point.

7 The total harmonic distortion is approximately proportional to the output voltage.

Vacuum Tube Data Sheets

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