Posted by manualblock [ 69.112.69.86 ] on July 19, 2005 at 10:44:43:

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.

Replies:

• Re: Fixed/cathode bias and AC - Rek_O_Kut 13:02:00 07/21/05 (4)
  • Re: Fixed/cathode bias and AC - Damir 14:51:07 07/21/05 (3)
    • Re: Fixed/cathode bias and AC - Thermionic 19:51:44 07/21/05 (2)
      • Re: Fixed/cathode bias and AC - Forty2wo 22:54:22 07/21/05 (1)
        • Re: Fixed/cathode bias and AC - Thermionic 13:34:57 07/22/05 (0)
• Re: Fixed/cathode bias and AC - Thermionic 01:26:06 07/20/05 (1)
  • Re: Fixed/cathode bias and AC - manualblock 14:22:10 07/20/05 (0)