"Dave Plowman (News)" wrote in message
...
In article ,
tony sayer wrote:
The standard all-valve "large screen" TV of the 50s/early 60s consumed
150W, of which half went into keeping the heaters alight. So a 250VA
transformer would have been plenty big enough.

Even so that was a very expensive component and the way TV design was
costed to the nearest fraction of a penny made it a no go!..

Yup - they left out the black level clamp from most sets and the cost of
those components would have been less than a transformer.


It was worse than that. The great majority of those sets also used the
abomination known as "mean-level AGC" In which the control voltage for AGC
to the RF and IF amplifiers by obtained simply by low-pass filtering the
negative going video signal found at the grid of the sync separator. So the
gain was wound up on low key scenes, and wound down on high-key scenes.
After this there was little point in trying to keep the black level
constant.. There were a few manufacturers brave enough to put TVs with gated
AGC and DC coupled video onto the market, but the GBP demonstrated that it
wasn't prepared to pay even a small premium for such trivial points as a
correctly presented picture, or decent sound. What mattered was the size of
the picture and what the cabinet looked like.

David.