The DC bias in a Class A amplifier:

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🔍 Key Concepts

• Class A amplifier operation and where the operating point (Q-point) is set on the characteristic curve • Relationship between grid voltage and cathode voltage in a vacuum-tube amplifier for normal conduction • What happens to tube current when the grid is made more negative or more positive with respect to the cathode

💭 Think About

• For a Class A tube amplifier to conduct for the entire input cycle, should the grid be biased so that the tube is already conducting with no signal, or just at cutoff? • If you make the grid increasingly negative relative to the cathode, does the plate (anode) current increase or decrease? What does that imply about typical bias polarity? • Which choice is consistent with a stable operating point roughly in the middle of the tube’s linear region?

✅ Before You Answer

• Verify how grid-to-cathode voltage (Vgk) is defined: grid potential minus cathode potential • Check tube characteristic curves: note the sign of Vgk values where the tube operates linearly for Class A service • Confirm that the chosen option matches the usual fixed or self-bias arrangement used in basic Class A audio/RF stages

🔍 Key Concepts

💭 Think About

✅ Before You Answer