31-10-2017, 03:11 PM
Hi.
You can still have DC restoration on mean level AGC or for that matter no AGC at all. If the level of the video changes on either mean level or no AGC the contrast level changes and that can give the viewer the misconception the brightness is changing. That is one reason with no or mean level AGC there were virtually no sets with DC restoration or fully DC coupling from the detector to CRT.
If you think back very few sets had AGC of any type prior to the 50's, the contrast was purely an IF or IF/RF gain control, some sets had either an attenuator for band one and some separate adjustable gain controls for band 1 & 3. That was the cheapest option and even on a well engineered set like the Murphy V310 that's how it was done. Actually mean level AGC was in some respects worse, on some Ekco sets picture flutter was a problem and I have heard that other makes had other issues.
The Pye V4 of 1953 put paid to a lot of this and did a good job of showing how 405 could really be like. Of course now with no aircraft flutter, signal fading etc, with the Aurora you can easily have direct coupling from detector to CRT or add a restorer diode, the difference is quite outstanding and worth doing to impress your friends!
You can still have DC restoration on mean level AGC or for that matter no AGC at all. If the level of the video changes on either mean level or no AGC the contrast level changes and that can give the viewer the misconception the brightness is changing. That is one reason with no or mean level AGC there were virtually no sets with DC restoration or fully DC coupling from the detector to CRT.
If you think back very few sets had AGC of any type prior to the 50's, the contrast was purely an IF or IF/RF gain control, some sets had either an attenuator for band one and some separate adjustable gain controls for band 1 & 3. That was the cheapest option and even on a well engineered set like the Murphy V310 that's how it was done. Actually mean level AGC was in some respects worse, on some Ekco sets picture flutter was a problem and I have heard that other makes had other issues.
The Pye V4 of 1953 put paid to a lot of this and did a good job of showing how 405 could really be like. Of course now with no aircraft flutter, signal fading etc, with the Aurora you can easily have direct coupling from detector to CRT or add a restorer diode, the difference is quite outstanding and worth doing to impress your friends!
