English Victor 625/405 line converter - UK Vintage Radio Repair and Restoration Discussion Forum

ENGLISH VICTOR · 6th Apr 2010, 6:11 am

Long before I was aware of the existance of this forum or of the excellent Aurora standards converter I needed a device for displaying my own 405 line receivers. Living in Australia did not help so I cobbled together a number optical converters of varying efficay. None of my converters ever did justice to my receivers. In view of the foregoing I designed and built a digital converter employing a mix of 74 and 74H ttl chips along with cmos memory and an off the shelf A/D and D/A converter chip capable of of operation with digital video signal proccessing. I had built a very touchy bucket brigade converter that I eventualy gave up on.

Essentialy the converter inputs 625 line mono or colour and derives from it all the timing pulses for the entire converter. These include 625 line vert timing 50Hz. 15625 Hz. fH. fH*810 for write clock 12.656250MHz. 8.201250 MHz. 405 line read clock and all the pulses required for memory bank commutation and 405 line sync and blanking etc.

The converter comprises two field stores that alternate between writing selected 625 lines and reading out as 405 lines. 256 levels of grey scale are used and to enable 5.25MHz video to be digitised the sample rate chosen was 12.656250 MHz to conform with the minimum Nyquist rate of 10.5 MHz. Chroma frequencies can be filtered out of the input if required by use of an on board jumper.

The memory stores already mentioned each have a storage of a little over 130K*8bits wide and is sufficient to store the required odd or even 405 line digitised picture without sync or blanking.

No interpolation between lines was attempted as this was my first foray into digital video manipulation, I wanted to prove my basic design first.

I have included some pictures of the device, built as a complete unit, one unit high conforming to standard 19" rack dimensions. The unit in total employs about 80 chips and about 20 discrete transistors along with a dozen or so diodes. I realize the unit is now old hat, it was built way back in 2003 and was retired following the purchase of an Aurora that has better performance due to it's excellent design and interpolation abilities as well as a super versatile R.F. modulator

The performance of my converter is such that it will operate directly from an unstable input such as a domestic VCR but the oputput signal timing is only as stable as the input. The problem of course can be eliminated by the use of a TBC following the VCR. The frequency response exceeds the 405 line standard. Clamping of the output signal is within 1% of blanking.

The output signal aproximates the input 625 line signal with every third line deleted. On programme material the lack of interpolation is not very noticeable on screens less than 12" diameter. The only user controls are power on/ff and still frame, frame capture.

I have included some pictures but the jpeg images do very little for the off screen shots. The other pictures are self explanatory, essentialy they show the converter from various angles and also show a sample of veroboard use, in this case a memory board is shown that employed 32K ram chips that was discarded in favour of a pair of cmos chips already described, the object was to show how versatile veroboard can be with a little patience. For a one off experiment making a set of P.C. boards would have not been a worthwhile proposition.

This simple converter has proven totaly trouble free to date (famous last words) it was switched on to-day for the first time in a few years and after a few moments came back to life. It has no built in R.F. modulator, I feed it into another home made device employing a sound /vision modulator xtal controled using a couple of MC1496 quadrant multipliers/ doubly balanced mixers operating on B1. That's another story.

Victor.

P.S. more details if required.

ppppenguin · 6th Apr 2010, 6:55 am

Victor

I thought I had fully documented the history of 625>405 conversion in a couple of articles I wrote for the BVWS Bulletin. I didn't know there was activity in Australia so you didn't make it into my hall of fame. I may have to write another sequel, so yes please, more details. Of both your early experimental converter and the successful framestore one.

ENGLISH VICTOR · 6th Apr 2010, 9:49 am

Jeffrey:

I was not aware of activity in Australia untill about 7 years ago, the interest here is of course minimal due to the tyrany of distance and the comparatively late entry in television broadcasting, late 1956. I believe I am the only one here who has successfully designed an electronic converter, not due to my expertise but due to lack of interest I imagine.

Certainly I will gather together some material for you including the bucket brigade converter if I can find it. Essentialy it comprised a number of charge transfer delay lines clocked at 13.3 MHz to store and read at 8.6189Mhz. with every third line deleted thus stretching 64uS to 98.76uS. The delay lines were used initialy as dropout compensator line stores in Panasonic domestic VCR's, around 1990 I seem to remember. Again no interpolation, the main problem was one of maintaing gain matching between lines. the gain of the chips drifted unequaly with temperature.

Victor.

P.S. I saw on utube a claim by a member who designed his own converter whilst asleep, built it and had it operating in two days and perfected it including two line interpolation in two weeks. All using ttl 74H chips. There were pictures on an old t.v but no details about the converter or pictures of it. It can be found by searching utube, "home made standards converter."

ppppenguin · 6th Apr 2010, 10:05 am

http://www.youtube.com/watch?v=w1DsM2_LApc
I remember that. We never did find out who emerald48 was or what methods he used. By 2007 when he did his converter the technology was relatively simple and available, certainly much easier than when I wrote my original articles.

dominicbeesley · 9th Apr 2010, 1:52 pm

Hello Victor,

That's an excellent result for a bit of homebrewing! Any more details will be welcome, also details of your modulator.

Cheers

Dom

ENGLISH VICTOR · 10th Apr 2010, 7:10 am

Dom, I will be posting details during the next month or so including details of the modulator.
Victor.

evingar · 10th Apr 2010, 10:26 am

Sterling effort !

I know what an undertaking it is to use TTL technology for that function. I had a stab at designing something myself a lot of years ago before CPLD's (etc) were generally available. Unlike you though, my design never saw the light of day. When push came to shove, I couldn't find the time to build it all onto veroboard and prove / debug it. I would be very interested in seeing the circuit diagram when you get the time to post it.

ENGLISH VICTOR · 11th Apr 2010, 9:35 am

Chris. Most of my circuits are free hand drawn but I will gladly send you what I have. Lots of block diagrams and a few calcs, notes and mods.
Victor.

dominicbeesley · 11th Apr 2010, 1:23 pm

Me too any scans would be welcome...I'm probably not going to build one but would like to know how you did it...I got an FPGA prototyping setup recently and it might make an interesting starter project!

Cheers

Dom

ENGLISH VICTOR · 11th Apr 2010, 1:42 pm

Dom: will do. I think I will send them to interested parties rather than continue the thread with lots of low res scans.
victor.

evingar · 11th Apr 2010, 2:46 pm

Quote:

Originally Posted by ENGLISH VICTOR

Chris. Most of my circuits are free hand drawn but I will gladly send you what I have. Lots of block diagrams and a few calcs, notes and mods.
Victor.

I'd love to see any info you have Victor - thanks

DangerMan · 11th Apr 2010, 4:29 pm

Me too, please Victor. I'd love to see anything you have.
Thanks,
Pete

Andrew2 · 12th Apr 2010, 8:47 pm

Victor -
An object lesson in skill and determination, and you deserve whatever accolades come your way.

I've always had an interest in video standards conversion since I saw the early BBC-2 showings of the imported U.S. Andy Williams Show with black borders and wondered 'why does it look like that?'
It took me weeks to figure out the various timings between 625/50 and 525/60 and whatnot to satisfy myself as to what they were doing.
There are some excellent PDF's on line from the BBC's archives about line-store, frame store and of course digital converters.
Well done again!

6th Apr 2010, 6:11 am	#1
ENGLISH VICTOR Hexode Join Date: Feb 2008 Location: Sydney, Australia Posts: 356	English Victor 625/405 line converter Long before I was aware of the existance of this forum or of the excellent Aurora standards converter I needed a device for displaying my own 405 line receivers. Living in Australia did not help so I cobbled together a number optical converters of varying efficay. None of my converters ever did justice to my receivers. In view of the foregoing I designed and built a digital converter employing a mix of 74 and 74H ttl chips along with cmos memory and an off the shelf A/D and D/A converter chip capable of of operation with digital video signal proccessing. I had built a very touchy bucket brigade converter that I eventualy gave up on. Essentialy the converter inputs 625 line mono or colour and derives from it all the timing pulses for the entire converter. These include 625 line vert timing 50Hz. 15625 Hz. fH. fH810 for write clock 12.656250MHz. 8.201250 MHz. 405 line read clock and all the pulses required for memory bank commutation and 405 line sync and blanking etc. The converter comprises two field stores that alternate between writing selected 625 lines and reading out as 405 lines. 256 levels of grey scale are used and to enable 5.25MHz video to be digitised the sample rate chosen was 12.656250 MHz to conform with the minimum Nyquist rate of 10.5 MHz. Chroma frequencies can be filtered out of the input if required by use of an on board jumper. The memory stores already mentioned each have a storage of a little over 130K8bits wide and is sufficient to store the required odd or even 405 line digitised picture without sync or blanking. No interpolation between lines was attempted as this was my first foray into digital video manipulation, I wanted to prove my basic design first. I have included some pictures of the device, built as a complete unit, one unit high conforming to standard 19" rack dimensions. The unit in total employs about 80 chips and about 20 discrete transistors along with a dozen or so diodes. I realize the unit is now old hat, it was built way back in 2003 and was retired following the purchase of an Aurora that has better performance due to it's excellent design and interpolation abilities as well as a super versatile R.F. modulator The performance of my converter is such that it will operate directly from an unstable input such as a domestic VCR but the oputput signal timing is only as stable as the input. The problem of course can be eliminated by the use of a TBC following the VCR. The frequency response exceeds the 405 line standard. Clamping of the output signal is within 1% of blanking. The output signal aproximates the input 625 line signal with every third line deleted. On programme material the lack of interpolation is not very noticeable on screens less than 12" diameter. The only user controls are power on/ff and still frame, frame capture. I have included some pictures but the jpeg images do very little for the off screen shots. The other pictures are self explanatory, essentialy they show the converter from various angles and also show a sample of veroboard use, in this case a memory board is shown that employed 32K ram chips that was discarded in favour of a pair of cmos chips already described, the object was to show how versatile veroboard can be with a little patience. For a one off experiment making a set of P.C. boards would have not been a worthwhile proposition. This simple converter has proven totaly trouble free to date (famous last words) it was switched on to-day for the first time in a few years and after a few moments came back to life. It has no built in R.F. modulator, I feed it into another home made device employing a sound /vision modulator xtal controled using a couple of MC1496 quadrant multipliers/ doubly balanced mixers operating on B1. That's another story. Victor. P.S. more details if required. Attached Thumbnails Last edited by ENGLISH VICTOR; 6th Apr 2010 at 6:29 am. Reason: Change one jpeg file

6th Apr 2010, 6:55 am	#2
ppppenguin Retired Dormant Member Join Date: Dec 2003 Location: North London, UK. Posts: 6,168	Re: English Victor 625/405 line converter Victor I thought I had fully documented the history of 625>405 conversion in a couple of articles I wrote for the BVWS Bulletin. I didn't know there was activity in Australia so you didn't make it into my hall of fame. I may have to write another sequel, so yes please, more details. Of both your early experimental converter and the successful framestore one.

6th Apr 2010, 9:49 am	#3
ENGLISH VICTOR Hexode Join Date: Feb 2008 Location: Sydney, Australia Posts: 356	Re: English Victor 625/405 line converter Jeffrey: I was not aware of activity in Australia untill about 7 years ago, the interest here is of course minimal due to the tyrany of distance and the comparatively late entry in television broadcasting, late 1956. I believe I am the only one here who has successfully designed an electronic converter, not due to my expertise but due to lack of interest I imagine. Certainly I will gather together some material for you including the bucket brigade converter if I can find it. Essentialy it comprised a number of charge transfer delay lines clocked at 13.3 MHz to store and read at 8.6189Mhz. with every third line deleted thus stretching 64uS to 98.76uS. The delay lines were used initialy as dropout compensator line stores in Panasonic domestic VCR's, around 1990 I seem to remember. Again no interpolation, the main problem was one of maintaing gain matching between lines. the gain of the chips drifted unequaly with temperature. Victor. P.S. I saw on utube a claim by a member who designed his own converter whilst asleep, built it and had it operating in two days and perfected it including two line interpolation in two weeks. All using ttl 74H chips. There were pictures on an old t.v but no details about the converter or pictures of it. It can be found by searching utube, "home made standards converter."

6th Apr 2010, 10:05 am	#4
ppppenguin Retired Dormant Member Join Date: Dec 2003 Location: North London, UK. Posts: 6,168	Re: English Victor 625/405 line converter http://www.youtube.com/watch?v=w1DsM2_LApc I remember that. We never did find out who emerald48 was or what methods he used. By 2007 when he did his converter the technology was relatively simple and available, certainly much easier than when I wrote my original articles.

9th Apr 2010, 1:52 pm	#5
dominicbeesley Octode Join Date: Nov 2004 Location: Hebden Bridge, West Yorkshire, UK. Posts: 1,885	Re: English Victor 625/405 line converter Hello Victor, That's an excellent result for a bit of homebrewing! Any more details will be welcome, also details of your modulator. Cheers Dom

10th Apr 2010, 7:10 am	#6
ENGLISH VICTOR Hexode Join Date: Feb 2008 Location: Sydney, Australia Posts: 356	Re: English Victor 625/405 line converter Dom, I will be posting details during the next month or so including details of the modulator. Victor.

10th Apr 2010, 10:26 am	#7
evingar Octode Join Date: Oct 2003 Location: Newbury, Berkshire, UK. Posts: 1,770	Re: English Victor 625/405 line converter Sterling effort ! I know what an undertaking it is to use TTL technology for that function. I had a stab at designing something myself a lot of years ago before CPLD's (etc) were generally available. Unlike you though, my design never saw the light of day. When push came to shove, I couldn't find the time to build it all onto veroboard and prove / debug it. I would be very interested in seeing the circuit diagram when you get the time to post it. __________________ Chris

11th Apr 2010, 9:35 am	#8
ENGLISH VICTOR Hexode Join Date: Feb 2008 Location: Sydney, Australia Posts: 356	Re: English Victor 625/405 line converter Chris. Most of my circuits are free hand drawn but I will gladly send you what I have. Lots of block diagrams and a few calcs, notes and mods. Victor.

11th Apr 2010, 1:23 pm	#9
dominicbeesley Octode Join Date: Nov 2004 Location: Hebden Bridge, West Yorkshire, UK. Posts: 1,885	Re: English Victor 625/405 line converter Me too any scans would be welcome...I'm probably not going to build one but would like to know how you did it...I got an FPGA prototyping setup recently and it might make an interesting starter project! Cheers Dom

11th Apr 2010, 1:42 pm	#10
ENGLISH VICTOR Hexode Join Date: Feb 2008 Location: Sydney, Australia Posts: 356	Re: English Victor 625/405 line converter Dom: will do. I think I will send them to interested parties rather than continue the thread with lots of low res scans. victor.

11th Apr 2010, 4:29 pm	#12
DangerMan Heptode Join Date: Jul 2009 Location: Stoke-on-Trent, Staffordshire, UK. Posts: 719	Re: English Victor 625/405 line converter Me too, please Victor. I'd love to see anything you have. Thanks, Pete

12th Apr 2010, 8:47 pm	#13
Andrew2 Nonode Join Date: Mar 2010 Location: Dukinfield, Cheshire, UK. Posts: 2,036	Re: English Victor 625/405 line converter Victor - An object lesson in skill and determination, and you deserve whatever accolades come your way. I've always had an interest in video standards conversion since I saw the early BBC-2 showings of the imported U.S. Andy Williams Show with black borders and wondered 'why does it look like that?' It took me weeks to figure out the various timings between 625/50 and 525/60 and whatnot to satisfy myself as to what they were doing. There are some excellent PDF's on line from the BBC's archives about line-store, frame store and of course digital converters. Well done again! __________________ Andy G1HBE.