🔍 Key Concepts

• Impedance matching between vacuum tube outputs (which are typically high impedance) and low-impedance headphones (75 ohms) • The normal function of a cathode bias resistor in a vacuum tube circuit • Why transformers are commonly used at the output stage of audio tube amplifiers

💭 Think About

• What is the typical impedance of a vacuum tube’s plate (anode) circuit compared to 75-ohm headphones? How are such mismatches usually handled in audio circuits? • What is the purpose of a cathode bias resistor in a tube circuit? Is it normally used as a load for headphones or for something else? • In practical radio/receiver designs using tubes, how are low-impedance speakers or headphones usually connected to the tube’s output?

✅ Before You Answer

• Verify how impedance matching transformers work to connect high-impedance sources to low-impedance loads • Confirm the typical role and current path of a cathode bias resistor and whether it is intended as an audio output load • Check whether both suggested methods are standard practice, or if only one is recognized as correct in typical vacuum tube headphone/output designs