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Television Standards Converters, Modulators etc Standards converters, modulators anything else for providing signals to vintage televisions.

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Old 21st Mar 2012, 11:22 pm   #1
FERNSEH's Avatar
Join Date: Mar 2005
Location: Gateshead, Tyne and Wear, UK.
Posts: 5,388
Default Sync pulse generator for 405 lines.

As a follow up to the Manor Supplies sync and blanking pulse generator topic I thought I'd knock up something similar for 405 lines.
The first picture shows the prototype unit. From top to bottom, the first chip is a 555 timer in an astable circuit to produce the twice line rate pulse train. The mark and space is 40 and 19 microseconds. This will become the frame sync broad pulses.
The second chip is a 74LS74 which is the divide by two device. Next down is a 74LS00 quad NAND gate, it is wired to act as a leading edge detector. The output from this IC is a 2microsecond spike which triggers two 555 timers.
One generates the 10 micro second line sync pulse and the other generates the 18 microsecond line blanking pulse.
The next stage of this construction will be the divider circuit to produce the 50Hz frame sync. I could employ 555 timers for this or perhaps three 74LS161 counters.
The reason for building this unit is that it will replace the rather crude valve circuits in a Cossor Alignment and Pattern generator. A single 6SN7GT twin triode does the pattern generation. It is pretty useless really at making a television signal but the rest of the instrument is a viable service aid.

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