Working Backwords ( Tube Cathode Stage )

Sometimes we are presented with an existing circuit that lists the values of the plate resistor and cathode resistor, but not the operating voltages or idle current.
We can work backwards from the resistor values to the operating points (if the B+ voltage is specified).

Plate voltage ( V+ )  volts *
Plate Resistor Rp (value of resistor between plate and power supply)  Ohms *
Cathode Resistor Rc  Ohms *
Ri (the internal plate resistance of the tube )  Ohms *
Tube gain (from tube manual or spec sheet)  mu *
* = required values


Chatode Current Ic  mA
Plate Voltage Vp  Volts
Grid - Chathode Voltage Vgc  Volts

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