1. Active Devices Vacuum tubes

2. Thomas Edison’s light bulb – Glass envelope – Vacuum – Filament

3. FILAMENT

4. Vacuum tubes Thermionic emission – Some metals will emit electrons when heated “Thermionic” = heat “Emission” = emit or shed

5. Fleming Valve Ambrose Fleming – Added a cathode and plate to Edison’s bulb – Created a two element device – Diode = two elements – Called it the valve

6. CATHODE PLATE FILAMENT

8. Vacuum tube diode When the charge on the plate is positive – current will flow When the charge is negative – no current flows

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11. Vacuum tube triode Lee Deforrest added a third element to the diode Triode = three elements

12. CATHODE PLATE GRID

13. Vacuum tube triode Third element called a grid Triode amplifies Deforrest called his triode the Audion

14. Vacuum tube triode Small fluctuations in current on the grid are amplified or magnified on the plate

15. + 10v 100v Bias voltage

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18. 10v 100v Audio in Audio out