The Tri-tet Oscillator

Author: J.B. Hoag

Fig. 29 H. A tri-tet oscillator circuit

Figure 29 H shows the circuit of an oscillator in which the same tube is used both as a triode and as a tetrode. It is a combination of the triode crystal oscillator and the electron-coupled oscillator. The output circuit L₂C₂ is electron coupled to the oscillator and electrostatically shielded therefrom by the suppressor and screen grids. One of the outstanding features of this oscillator is that the tank circuit L₂C₂ can be tuned to either the fundamental crystal frequency or one of its multiples. The cathode tank circuit L₁C₁ is tuned to a frequency somewhat higher than that of the crystal.

The tuning procedure for this oscillator is very much like that of the previously described crystal oscillators. The plate current dip however is symmetrical. After initial adjustment, the cathode condenser C₁ is to be readjusted to obtain maximum power output. Its value should be as small as possible in order to prevent overheating the crystal.