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Calculating Cathode Bias Resistor

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Calculating Cathode Bias Resistor

Postby Augustica.com » 07 Aug 2013, 13:21

The most widespread method to bias a cathode is to insert a cathode bias resistor between the cathode and ground, and connect the grid of the tube to the ground via a grid leak resistor.

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Having selected our operating point at 85V, we know anode, and hence, cathode current. (In triode anode and cathode currents are equal). We know the value of Vgk we need - it has to be 2V below the potential of the cathode. If the greed is at 0V, the cathode has to be at +2V. If we know the voltage across, and the current through, an unknown resistor, we can find the value of the resistor through Ohm's law.

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We know that the cathode voltage is 2.0V, so the cathode bias resistor R3 will have value of 363 Ohm. The closest standard value is 360 Ohm.

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