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Heatercathodeshort · 2nd Mar 2015, 9:53 am

Weird! It looks as if the contrast is too high and the brightness a bit low. With a low emission tube viewed in a darkened room you should be able to adjust the brightness and contrast to get a fully graded picture but with very little actual light output from the CRT. Your pictures appear to show what I call the 'soot and whitewash' effect usually produced by a video amplifier fault. Check the D77 detector, C22 4uf and the effect of disconnecting any connections to pin 1 of the D77 vision int. limiter section. C23 couples the video output to the cathode of the CRT and is worth a check if you have not done so.
Later, I will post some pictures from the screen of my VC53DA producing the effect of a low emission CRT. [Resistor connected across tube heater] Must do some work first! J.

2nd Mar 2015, 9:53 am	#122
Heatercathodeshort Dekatron Join Date: Jun 2005 Location: Warnham, West Sussex. 10 miles south of DORKING. Posts: 9,147	Re: Marconiphone VRC74DA Weird! It looks as if the contrast is too high and the brightness a bit low. With a low emission tube viewed in a darkened room you should be able to adjust the brightness and contrast to get a fully graded picture but with very little actual light output from the CRT. Your pictures appear to show what I call the 'soot and whitewash' effect usually produced by a video amplifier fault. Check the D77 detector, C22 4uf and the effect of disconnecting any connections to pin 1 of the D77 vision int. limiter section. C23 couples the video output to the cathode of the CRT and is worth a check if you have not done so. Later, I will post some pictures from the screen of my VC53DA producing the effect of a low emission CRT. [Resistor connected across tube heater] Must do some work first! J. Last edited by Heatercathodeshort; 2nd Mar 2015 at 10:02 am.