Re: Nearly a Sobell 1000 DST!!
The operation of a stabilised line output stage was explained in the "Recent Developments" section of the 1960/61 Radio and Television servicing book. In fact Peto-Scott introduced something similar in their 1957 range of TVs, the models TV1720 etc. Peto-Scott called the arrangement an EHT regulation circuit.
The circuit is essentially an AGC system so that width and EHT is maintained regardless of mains voltage variations, also compensates for valve aging.
Remember that the line output valve functions as a switch and the stabilising circuit controls the conduction of the valve hence the amount of energy supplied into the line output transformer primary.
DFWB.
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