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1100 man · 19th Feb 2018, 11:03 am

After some probing about with the scope last night, I discovered that what started as nice clean line pulses at the anode of the PCL84 sync separator, got steadily noisier as the contrast was reduced. The video going in stayed nice and clean, but at minimum contrast the pulses coming out were lost in the noise.
A new PCL84 solved that- good clean pulses at minimum contrast and no line tearing. Bit of a shame as that was a 'Marconophone' branded valve so might well have been an original.
Next problem is random shifting of the picture from side to side by about 1/4 inch. Looks like the phase of the line oscillator is changing slightly so that's tonight's investigation.
Cheers
Nick

19th Feb 2018, 11:03 am	#20
1100 man Octode Join Date: Apr 2016 Location: Ventnor, Isle of Wight, & Great Dunmow, Essex, UK. Posts: 1,377	Re: Marconiphone VT161 17" TV After some probing about with the scope last night, I discovered that what started as nice clean line pulses at the anode of the PCL84 sync separator, got steadily noisier as the contrast was reduced. The video going in stayed nice and clean, but at minimum contrast the pulses coming out were lost in the noise. A new PCL84 solved that- good clean pulses at minimum contrast and no line tearing. Bit of a shame as that was a 'Marconophone' branded valve so might well have been an original. Next problem is random shifting of the picture from side to side by about 1/4 inch. Looks like the phase of the line oscillator is changing slightly so that's tonight's investigation. Cheers Nick