*Question G4A04:
What is the effect on plate current of the correct setting of a vacuum-tube RF power amplifier’s TUNE control?*  

*Correct Answer is  B: A pronounced dip*  

### AI Response: (may contain errors)  

In a vacuum-tube RF power amplifier, the TUNE control is used to adjust the resonant frequency of the tank circuit to match the operating frequency. This ensures maximum power transfer from the amplifier to the load (usually an antenna).

1. **Correct Answer: A pronounced dip**

   - When the TUNE control is correctly adjusted, the tank circuit is at resonance. At resonance, the impedance of the tank circuit is purely resistive, and the reactive components (inductive and capacitive) cancel each other out.
   - This results in maximum power transfer to the load and a minimum amount of power being dissipated in the tube itself.
   - Consequently, the plate current, which is the current flowing through the tube, will show a pronounced dip at the point of resonance because less current is needed to achieve the same power output.

2. **Why the other choices are incorrect:**

   - **B: A pronounced dip** is the correct answer, as explained above.
   - **C: No change will be observed** is incorrect because adjusting the TUNE control affects the resonance condition, which directly impacts the plate current.
   - **D: A slow, rhythmic oscillation** is incorrect because the TUNE control adjustment should not cause oscillations in the plate current. Oscillations would indicate instability or improper tuning.

3. **Useful Concept:**

   - At resonance, the impedance of the tank circuit is minimized for the given frequency, leading to efficient power transfer and a dip in plate current. This is a key indicator that the amplifier is properly tuned.