12AX7/ECC83

                     APPLICATION NOTES

MICROPHONICS

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%.

HUM

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.


[Schematic of phase inverter circuit omitted from text file]


    Supply Voltage                      250    350 volts
    Cathode Resistance                 1200    820 ohms
    Total Cunent                       1.08   1.70 mA
    Output Voltage[6] (RMS)              35     45 volts
    Voltage Gain                         58     62
    Percent Distortion[7]               5.5    3.5 %






[6] Eo at grid current starting point.
[7] The total harmonic distortlon is approximately proportional to the output
voltage