| Fixed/cathode bias and AC [message #9083] |
Tue, 19 July 2005 09:44  |
Manualblock
Messages: 4973
Registered: May 2009
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Illuminati (13th Degree) |
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Thanks all for doing a great job in explaining this.
So fixed bias is derived from a voltage divider and a cap on the input AC signal. It has the advantage of allowing the tube to be operated at a fixed Vg.
Self-bias uses a resistor to react to changes in the signal by following Ohm's law and causing a plate voltage drop to change with the Vg.
The self-bias is self regulating and must operate in class A. It is easier to design due to the self-regulating properties of the circuit.
AC component on the plate voltage is removed by the by-pass cap.
Now why would anyone go to the trouble of using grid leak bias when they could just use the cathode bias? It seems so simple.
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