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Active Devices

Active Devices. Vacuum tubes. Vacuum tubes. Thomas Edison’s light bulb Glass envelope Vacuum Filament. FILAMENT. Vacuum tubes. Thermionic emission Some metals will emit electrons when heated “Thermionic” = heat “Emission” = emit or shed. Fleming Valve. Ambrose Fleming

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Active Devices

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  1. Active Devices Vacuum tubes

  2. Vacuum tubes • 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. PLATE CATHODE FILAMENT

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

  8. _ - - - - - - - - - -

  9. + - - - - - - - - - -

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

  11. PLATE GRID CATHODE

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

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

  14. + Bias voltage 100v 10v

  15. + + + + + - - - - - - - - - - -

  16. + + + + + - - - - - - - - - - -

  17. Audio out Audio in 100v 10v

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