the output of comparator 146 is applied to a transistor 148 that is interconnected with a transistor 150 and an amplifier 152 one input of the amplifier 152 is connected to the output of the amplifier 88 the output of amplifier 88 is also interconnected between transistors 148 and 150 the elements 148 150 and 152 function as an emitter main beam clamp by comparing fig3 and 5a and 5b it will be appreciated that fig3 is a somewhat simplified block diagram of the circuits shown in fig5 a and 5b in fig3 certain control lines and elements were eliminated to emphasize the primary operation and function of the present invention however the control lines and elements omitted in fig3 have been shown and described in fig5 a and 5b in fig6 a block diagram of the delay unit 46 of fig3 is shown the real time video signal on line 111 is applied to analog to digital converter 180 that converts the amplitude of the video signal into an 8 bit word the 8 bit word from the converter 180 is transferred through a buffer 182 to a random access memory 184 a digital word corresponding to the amplitude of the video signal delayed by one scan cycle is read from the memory 184 into the latch 188 and this word is then converted into the delayed video signal by the digital to analog.