Question
What is the effect on plate current of the correct setting of a vacuum-tube RF power amplifier’s TUNE control?
Answer Options
- A) A pronounced peak
- B) A pronounced dip
- C) No change will be observed
- D) A slow, rhythmic oscillation
Correct Answer: B
Explanation
Vacuum tube RF power amplifiers require careful tuning to ensure maximum power transfer to the antenna and to achieve the highest efficiency. The ‘TUNE’ control adjusts the resonant frequency of the plate (output) tank circuit to match the operating frequency.
When the tank circuit is properly tuned to resonance, the impedance presented to the tube’s plate is maximized, resulting in the minimum flow of DC plate current, which is observed as a pronounced dip on the plate current meter. This dip indicates that the amplifier is optimally coupled, reducing unnecessary heating and maximizing RF output power.
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