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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 12th Apr 2023, 2:45 pm   #1
Chris55000
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Default David's TTL 405/625 Standards Converter Circuit Diagram

I have started work on new Circuit Diagrams for David's TTL 405/625 Standards Converter, but so far I have only been able to daw the 10.125 MHz V.C.O. and the first divide-by-4 stage, as the resolution of the extract posted here in the Thread "TTL Standards Converter Re-Comissioned" is too low to decipher much more!

I have PM'd Dave for a copy of his notes/scans and await his response, but in the meantime I have posted what I've worked out so far!

Dave has said he's happy to share them, and if I can get a copy of his scans I can re-draw them much more quickly than he may have time to do!

Chris Williams
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File Type: pdf Preliminary Extract of 405-625 Timing Dividers.pdf (186.6 KB, 208 views)
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Old 12th Apr 2023, 4:59 pm   #2
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Default Re: David's TTL 405/625 Standards Converter Circuit Diagram

I take my hat off to Dave for designing a piece of equipment that isn't subject to the vagaries of FPGA supplies and horribly expensive CCD chips, I'm afraid I don't have the digital design skills to dream up something as sophisticated as that I'm afraid!

What I can do, once I have the necessary circuit information and component values, is to provide a magazine–quality write–up and PCB designs, if Dave furnishes me with photos of the board top and bottom sides, and a top and bottom photo of the Veroboard shown in his prototype – I also would like to build one myself!

Chris Williams
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Old 12th Apr 2023, 5:14 pm   #3
Electronpusher0
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Default Re: David's TTL 405/625 Standards Converter Circuit Diagram

Very good, I may be tempted to build one myself.
Keep up the good work.

Peter
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Old 12th Apr 2023, 7:40 pm   #4
Vintage Engr
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Default Re: David's TTL 405/625 Standards Converter Circuit Diagram

I'm watching this one with interest, it sounds brilliant.
Thanks to all who are so far involved.

David.
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Old 12th Apr 2023, 8:44 pm   #5
greg_simons
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Default Re: David's TTL 405/625 Standards Converter Circuit Diagram

I built the heghog mk2 but I'm watching this space with great interest!.
Greg.
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Old 12th Apr 2023, 8:55 pm   #6
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Default Re: David's TTL 405/625 Standards Converter Circuit Diagram

Hi Chris,
that's not the only part of the 625 clock pulse and timing board. The 74LS625 oscillator IC is controlled by a frequency and phase discriminator.
The PCB supplies the control pulses to the 405 sync and blanking generator and provides the line store write functions. The clock frequency should be increased to 12Mhz, not the precise frequency.
Also the 98.8uS reference pulse train to the 405 timing board which provides the lower frequency clock pulses and timing for the read functions.
The truth is the whole converter needs a complete review in order to simplify the design. The design dates back to the mid to late eighties.
I'm considering replacing the static RAMs in the line store boards with FIFOs.

DFWB.
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Old 13th Apr 2023, 2:26 pm   #7
Chris55000
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Default Re: David's TTL 405/625 Standards Converter Circuit Diagram

Afternoon Dave!

The results I've seen in your "Standards Converter Recomissioned" thread are more than adequate enough (certainly with my eyesight!) for me to be happy to build the design as it is without waiting for to you to review and update it, and I would much prefer to experiment with your original as pictured in your thread, which was the idea behind my PM requesting the original circuits, and I think the idea is other Members may want to try the same as well!

If you feel the design is inadequate "as-built" by all means see if can update it to your satisfuction, but there is a large and growing Q for the circuits "as-is", so if you could see a way to letting myself or another Member have a copy of your original notes and sketches before you dispose of them I'd be ever so grateful!

Chris Williams
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Old 13th Apr 2023, 3:11 pm   #8
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Default Re: David's TTL 405/625 Standards Converter Circuit Diagram

Hi Chris,
bear in mind the performance of this converter is no where as good as the Hedghog and Aurora converters. It is a pretty crude design built in the 1980s when no other converter was available. Built at at a time when the shop at it's busiest and served as a source of System A signals until 2006 when the first Aurora converter came available.
However in the late 1990s a very simple converter was built which gave promising results. A FIFO was employed in the line store. Indeed it was going to be the basis of a 405 line NTSC converter to supply colour signals to the Pye 405 line CTV which was made in 1956. The FIFO converter disappeared after it was given to another radio and TV collector. I now use a special Aurora 405 line NTSC converter, only one of three made.

DFWB.
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Old 13th Apr 2023, 3:14 pm   #9
Chris55000
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Default Re: David's TTL 405/625 Standards Converter Circuit Diagram

. . .I have noted your first comment, but none the less it would not discourage me from having a go, and I suspect other Members would probably be aware they can't get "Aurora" or "Hedgehog" performance from it, but nothing beats the pleasure of trying something out and experimenting!

. . .As I said in my first post with the re–drawn schematic extract, it was drawn from the very poor resolution "7_schematic clock and timing board" that the Forum Software posts by the time it's uploaded – a scan of your original drawing would be much easier to follow and redraw!

. . .I'm afraid I was neither rich enough, lucky enough nor have the space at home to experiment with a 405–line "pre–colour TV–era" prototype NTSC set, but I live in hope that one day (during retirement perhaps!) I can design and build my own "Tyne Style 1974 Colour Set" with a delta–gun CRT, the Mullard 4 chip decoder and and a mains–isolated chassis!

Chris Williams

PS!

(I do have a few Hedgehog parts as well as the FPGA Dev. Mod and PCB to build the first version but the original Multicomp cases are proving unobtainable at the time I write this, so that's on the "back burner" until I can get another case and I haven't the loot to buy a Hedgehog already made from "Freya" Steve for a good few months yet!)
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Old 14th Apr 2023, 10:06 am   #10
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Default Re: David's TTL 405/625 Standards Converter Circuit Diagram

Quote:
Originally Posted by FERNSEH View Post
I now use a special Aurora 405 line NTSC converter, only one of three made.
DFWB.
Hi All
Apologies for ‘butting in’ but I have been wondering for some time about the total ‘head count’ of 405 line NTSC Auroras ‘in captivity’ - I have one bought directly from Darryl in the US and I was under the impression that there was another one ‘at large’ in Ireland - I doubt if the three mentioned include these but, either way it would be useful to have an accurate count of the total in existence as it is unlikely that any more will be made - I’ll butt back out again now

Rgds to all - keep up the good work

John
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