Square Waves Produced by Blocking Action

Author: J.B. Hoag

In Fig. 30 D, the 110-volt, 60-cycle current is rectified by the 6H6 tube and develops a direct pulsating voltage across R₁. The 6SJ7 tube operates with zero bias. The strong negative pulses from R₁ drive its plate current to zero, i.e., block the tube. The resultant voltage changes across R₂ are of reasonably square wave-form. With a large time constant RC in the output circuit, this wave-form appears across the output terminals. R can be 100,000 ohms and C can be 4 µfd., as in Fig. 30 A. Obviously both of the square-wave generators just described can be operated at other than 60 cycles by suitable changes in the various circuit constants.

Fig. 30 D. A circuit for changing 60-cycle sine waves into 60-cycle square waves by blocking action. Sharp pulses will be obtained if the time constant RC is made very small