[FERNSEH]

An effective vision AGC system. Earlier Ultra TVs employed a frame gated AGC system. This is much easier to implement than line sync sampling. The black level is sampled during the frame blanking period which means a sample of much long duration can be obtained, and no knife edge timing required. Possibly the only disadvantage of the this system is the long time constants required to smooth the AGC voltage.
Models V16-60 and W21-60 employ this system of vision AGC. A Mazda 6D2/EB91 is employed as the APC gating pulse limiter and APC rectifier. The negative going gating pulse comes from the anode of the frame blocking oscillator.
I'll post up the circuit of this AGC system later today.
Information for the V17-60 can be found in the 1957/58 R & T servicing book.

DFWB.