Two A.C. generators and 1 uf capacitor is added to run as simulation. 20 K resistor is where Rochelle Salt Crystal Microphone ( 10 to 100 mV output) would go. Note microphone cable is shielded line in. These microphones were sensitive to moisture and somewhat fragile.
Triode tubes that might be used were # 56, 27,37,76 with the heater circuit not shown in simulation.
Example of tube 56, is heater voltage 2.5 volts (A.C. or D.C.) at 1 amp. Plate current 2.5 to 5 milliamps for 13.8 amplification factor.
