🔍 Key Concepts

• AC filament supply in radio/electronics and what it powers • How AC vs DC on a filament can affect hum/noise in an audio amplifier • What is meant by "mostly for practical reasons" in equipment design

💭 Think About

• Ask yourself: Why might engineers choose an AC filament supply instead of DC in many older amplifiers or radios? Think about power transformer windings and simplicity. • Consider whether an AC filament is more likely to reduce hum or introduce hum into an amplifier’s audio output. • Look at choice C: Under what condition would both statements about practicality and hum behavior be true at the same time?

✅ Before You Answer

• Be clear on whether AC on filaments tends to add hum or eliminate hum in sensitive audio stages. • Decide if the fact that AC is easily available from a transformer is a valid design reason for using it. • Before picking an answer, ask: can both A and B be correct at the same time, or does one contradict the intended reason for use?