Quote:
Originally Posted by 1100 man
There are certainly some odd looking bits to the circuit- Fernseh must have been right when he said they used some dodgy circuit techniques! Why, for instance, does the main HT rail go to the frame scan coils? I've never seen that before!
Cheers Nick
|
A small amount of DC component will be introduced into the frame scanning coils which will cause a degree of picture shift. Also, because the resistors R92 & R93 are inserted before the main smoothing capacitor a tiny amount of 50Hz ripple will be present in the scanning coils. Why would the designer want to do that?
What is clear is that this circuit feature is present in all the Ultra and Pilot 1959/60 110 degree CRT models.
Some models such as the Ultra V17-70 have frame flyback suppression. A negative going pulse from the frame oscillator is supplied to the CRT grid.
Later models including the V17-80 "Bermuda" retain the wonderful CRT drive arrangement but instead of the high level contrast control system the contrast control is in the mean level vision AGC circuit.
It's worth mentioning that the high level contrast control was a circuit feature in many other TVs which were made by other manufacturers. Well known models that come to mind are the Pye dual standard models 3 and 11. Also many mid 1950s EMI sets including the 1824 and 1840 series of models.
DFWB.