Subelement A: — Topic :
Question 6A400
Element 6 (Radiotelegraph)In a self-biased RF amplifier stage: plate voltage is 1250 V, plate current 150 ma, grid current 15 ma,grid-leak resistance of 4000 ohms, what is the operating grid bias?
Explanation
In a self-biased RF amplifier utilizing grid-leak bias, the operating grid bias is developed by the flow of grid current through the grid-leak resistor. This is a direct application of Ohm's Law.
The grid current (I_grid) of 15 mA (or 0.015 Amperes) flows through the grid-leak resistance (R_grid-leak) of 4000 ohms. The resulting voltage drop across this resistor creates the negative grid bias (V_bias).
Using Ohm's Law:
V_bias = I_grid × R_grid-leak
V_bias = 0.015 A × 4000 Ω
V_bias = 60 V
This 60V makes the grid negative with respect to the cathode, providing the necessary bias for class C or other operating modes. The plate voltage and plate current are not used in calculating grid-leak bias. Therefore, 60 V is the correct operating grid bias.
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