Subelement A: — Topic :
Question 6A387
Element 6 (Radiotelegraph)Given a vacuum tube of the following characteristics: plate voltage 1000 V, plate current 127 ma,filament current 5.4 amp, mutual conductance 8000 microvolts, and amplification factor of 25. What isthe correct volume of negative grid bias for Class B amplifier?
Explanation
For Class B amplifier operation, the vacuum tube's grid is biased to the approximate plate current cutoff point. This ensures that plate current flows for only one-half of the input AC cycle.
The cutoff bias voltage (Ec) can be calculated using the formula:
Ec = -Ep / μ
Where:
* Ec is the cutoff bias voltage
* Ep is the plate voltage
* μ (mu) is the amplification factor
Given a plate voltage (Ep) of 1000 V and an amplification factor (μ) of 25:
Ec = -1000 V / 25 = -40 V
Thus, a negative grid bias of 40 V is required for Class B operation. The other provided parameters (plate current, filament current, and mutual conductance) are not used in determining the cutoff bias voltage. Other bias values would place the tube in a different operating class.
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