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Heatercathodeshort · 1st Mar 2015, 8:57 pm

The picture has the appearance of vision clipping or overload of the video amplifier. Make sure the int. limiter is set to zero. The contrast control should be about mid way for a normally contrasted picture. Check the two anode loads on the VA stage 2.2K and 6.8K and the Z77 itself. A flat tube will normally produce a correctly contrasted picture when viewed under blacked out lighting conditions but will of course be very dark. Any attempt to improve this by advancing contrast or brightness will result in the picture turning negative with a 'satin' appearance. This does not appear to be the case from your pictures but may be the case due to camera enhancement. Any attempt to boost EMI tubes can result in an O/C heater or complete loss of any emission the tube may have. J.

1st Mar 2015, 8:57 pm	#118
Heatercathodeshort Dekatron Join Date: Jun 2005 Location: Warnham, West Sussex. 10 miles south of DORKING. Posts: 9,147	Re: Marconiphone VRC74DA The picture has the appearance of vision clipping or overload of the video amplifier. Make sure the int. limiter is set to zero. The contrast control should be about mid way for a normally contrasted picture. Check the two anode loads on the VA stage 2.2K and 6.8K and the Z77 itself. A flat tube will normally produce a correctly contrasted picture when viewed under blacked out lighting conditions but will of course be very dark. Any attempt to improve this by advancing contrast or brightness will result in the picture turning negative with a 'satin' appearance. This does not appear to be the case from your pictures but may be the case due to camera enhancement. Any attempt to boost EMI tubes can result in an O/C heater or complete loss of any emission the tube may have. J.