The Grounded-Base Amplifier

Author: N.H. Crowhurst

The grounded-base transistor amplifier is very like the grounded-grid vacuum-tube amplifier. In the vacuum-tube amplifier there is no current in the grid connection to ground. In the transistor amplifier, this current is small compared to that in the emitter and collector connections. In addition, only small voltages are needed to cause the necessary current fluctuations in the emitter circuit, whereas (by using a higher voltage and a high resistance in the collector connection) much higher voltages can be obtained at the collector.

This gives us a clue to how the transistor can be used to amplify. If the grounded-grid amplifier is like the grounded-base transistor, we should find that the tube grid is like the base of a transistor, the cathode like the emitter (they even sound similar, because a cathode is used to emit electrons), and we must always remember that voltages control electron flow in a tube, whereas currents (or electron distribution) control voltage and current effects in a transistor.

Comparing grounded-grid and grounded-base amplifiers