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FERNSEH · 12th Jul 2018, 1:37 pm

Hello Jac,
Despite the use of the very modest video amplifier valve, a PCF80 the contrast ratio is excellent on both line standards.
Decca addressed the TV system demodulator switching demands by employing separate diodes and associated components for each transmission standard.

The output from the demodulator is AC coupled and then DC restored and supplied to the grid of the PCF80 V9a. As the DC restorer is of the sync tip type this might result in slight differences in the black levels between 625 and 405, assuming that is the 405 sync height is 30% of peak white level and 625 is 25%.

DFWB.

12th Jul 2018, 1:37 pm	#74
FERNSEH Dekatron Join Date: Mar 2005 Location: Gateshead, Tyne and Wear, UK. Posts: 7,444	Re: Decca DR101 dual standard TV Hello Jac, Despite the use of the very modest video amplifier valve, a PCF80 the contrast ratio is excellent on both line standards. Decca addressed the TV system demodulator switching demands by employing separate diodes and associated components for each transmission standard. The output from the demodulator is AC coupled and then DC restored and supplied to the grid of the PCF80 V9a. As the DC restorer is of the sync tip type this might result in slight differences in the black levels between 625 and 405, assuming that is the 405 sync height is 30% of peak white level and 625 is 25%. DFWB. Attached Thumbnails