Journal of the Society of Motion Picture and Television Engineers (1950-1954)

Fig. 14. Bi-stable multivibrator. external 60-cycle reference. The chassis also contains a single binary counter stage which provides 15.75-kc pulses to the pulse former chassis. The master oscillator panel contains the only circuit controls in the synchronizing pulse generator. They are: the frequency control for the oscillator, a phasing control for adjusting the phase of the 60-cycle lock-in, and a bias control on the reactance tube. The reactance-tube current may be read on the front panel meter. This enables the synchronizing pulse generator to be locked to the reference frequency at the center of the AFC control range without the necessity of external test equipment. The counter chassis consists of ten binary counter stages which are made to provide a count of 525 by means of pulse feedback. The chassis accepts 31.5-kc pulses from the master oscillator and furnishes a pulse at 60-cycle rate to the pulse-forming circuits. Other outputs at various points along the divider chain are also used in the pulse-former in the interest of overall simplification. The binary type counter is a very simple and very stable circuit requiring no adjustments whatsoever. The pulse-former chassis accepts outputs from the master oscillator and divider chassis and generates the desired output waveforms. All timing of pulse widths, including the equalizing and vertical-synchronizing pulse-gating waveforms, are determined by a delay line or by pulse counting by means of binary stages. Thus, once the desired pulse widths are chosen there is no need for further adjustment. A generalized form of the circuit used to generate the output pulses is shown in Fig. 14. It is seen to be a variation of the well-known EcclesJordan trigger circuit which is now known as a bistable multivibrator. This latter term is quite explicit since the circuit has two stable conditions: one in which tube A is fully conducting and tube B completely cut off; the other with tube B fully conducting and tube A cut off. It may be transferred from one condition to the other by a number of triggering means. For instance, if a trigger is applied to a point which is common to both triodes, such as the cathode connection, a transition from one condition to the other occurs with each trigger pulse. If the circuit is to be used to generate a pulse of a particular duration, triggers corresponding in time to the leading and trailing edges of the required pulse may be applied respectively to the points "a" and "b". A transition from one stable state to the other occurs upon arrival of the leading-edge trigger and a return to the original stage occurs upon arrival of the trailing-edge trigger, thus causing the circuit to generate a pulse of a duration corresponding to the time interval between the leading and trailingedge triggers. The circuit is used in this manner to generate both horizontal and vertical rate pulses. In the case of the horizontal pulses, triggers of the correct timing are obtained from a delay line. Vertical-rate triggers are obtained from the main divider and from a secondary divider chain which operates in conjunction with the main divider. The synchronizing signal generator power supply furnishes unregulated 200 v to all circuits except the pulse clippers and the master oscillator. The voltages for these circuits are regulated by means of a pair of VR tubes. The a-c power consumption is 250 w. L. L. Pourciau: Television Camera 177