Question
What is the correct adjustment for the LOAD or COUPLING control of a vacuum tube RF power amplifier?
Answer Options
- A) Minimum SWR on the antenna
- B) Minimum plate current without exceeding maximum allowable grid current
- C) Highest plate voltage while minimizing grid current
- D) Desired power output without exceeding maximum allowable plate current
Correct Answer: D
Explanation
The ‘LOAD’ or ‘COUPLING’ control on a vacuum tube RF power amplifier adjusts the coupling between the final stage and the antenna load. Proper adjustment of this control is performed in conjunction with the ‘TUNE’ control to ensure stability and efficiency.
The correct procedure is to adjust the controls to achieve the desired power output without exceeding the maximum allowable plate current (or cathode current, depending on the amplifier design). Exceeding the maximum plate current can rapidly overheat and destroy the expensive vacuum tube. The operator generally adjusts the load control to slightly broaden the dip of the plate current (from the TUNE adjustment) to safely deliver the desired power.
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