Subwoofer and oil lamp: what they have in common

1. Step 1. Subwoofer — has part — Amplifier. A built-in amplifier.
2. Step 2. Amplifier — has part — Triode. Tube amplifiers.
3. Step 3. Triode — is made of — Tungsten. The filament is tungsten.
4. Step 4. Tungsten — is material for — Incandescent light bulb. A tungsten filament (since 1904–1910).
5. Step 5. Incandescent light bulb — evolved from — Oil lamp. The electric lamp replaced oil and gas lamps.

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