Piezo-Electric Oscillator Circuits with Four-Electrode Tubes

Two new piezo-oscillator circuits using the screen-grid tube are described. One circuit uses feedback through the crystal, which has two pairs of electrodes with connections to the anode, control grid, and filament of the tube. In the other circuit the two electrodes of the crystal are connected. between the anode and control grid. The new circuits are unusually stable and at low frequencies give greater power output than the three-electrode tube circuits. They are particularly useful at those low frequencies for which flexural vibrations are employed. When oscillating at flexural vibration frequencies crystals show a tendency to creep lengthwise until a position is reached which gives maximum power output. If the crystal is displaced from this position it will return to it again.