405 NTSC colour - UK Vintage Radio Repair and Restoration Discussion Forum

ppppenguin · 7th Sep 2004, 6:08 pm

There's a possibility that Darryl may reprogram the Aurora standards converter to do 405 NTSC out.

Any interest?

See also:

https://www.vintage-radio.net/forum/showthread.php?t=948

evingar · 7th Sep 2004, 10:04 pm

Hi Jeffrey

While I am (mightily!) impressed that this can be done. I am **Really** struggling to think of where the feature might be used.

The only possibility that comes to mind is if someone has old broadcast equipment that was used in the early days of colour TV implementation. I seem to remember that NTSC 405 lines were broadcasted experimentally for a time. I believe there was a magazine article on this a while back (405 Alive?).

Chris

jim_beacon · 7th Sep 2004, 10:09 pm

There are a small number of the experimental 405 NTSC sets still in existence, but only two or three, I think - can you confirm Jeffrey?

Jim.

Steve_McVoy · 7th Sep 2004, 10:46 pm

David Boynes is restoring one:

http://www.earlytelevision.org/pye_experimental_color.html

http://www.earlytelevision.org/pye_color_restoration.html

ppppenguin · 8th Sep 2004, 7:43 am

Not sure exactly how many of these experimental sets survive but probably fewer than 5.

Duke_Nukem · 8th Sep 2004, 8:47 am

How many manufacturers do you rekon actually made the odd experimental set ? I assume it was really just the big boys ?

Theres an interesting two-part artical in Wireless World (1956) on the Murphy one.

TTFN,
Jon

David_Robinson · 8th Sep 2004, 4:02 pm

I guess it wouldn't be too difficult to modify a dual standard colour set to work on 405 NTSC instead of 625 PAL. Would that make the set more authentic or less?

Retune the bandpass filter and notch filter, fit a new crystal, defeat the PAL switch and shift the chroma phase by 33° - job done! Now where can I get a set?

ppppenguin · 8th Sep 2004, 5:09 pm

I don't think you need the 33 degree shift. You can consider NTSC as modulated on the U and V axes. You can modulate and demodulate on those axes. The only thing you lose is the wider I bandwidth. I believe that very few coders or sets actually use the I and Q axes with their different bandwidths.

David_Robinson · 8th Sep 2004, 7:33 pm

Yes, of course you're right. Look, it's 12 years since I worked on NTSC...

Mike Phelan · 9th Sep 2004, 11:46 am

You may have to add a 'tint' control for the ref osc phase, so you can correct for lilac or puce skin-tones, that NeverTwiceSameColour was renowned for!

David - thought I recognised the name - are you a fellow ex-'Television' scribe?

David_Robinson · 13th Sep 2004, 4:07 pm

Good grief, that's going back a bit! My finest hour - the March 1974 issue with my home-built colour set on the cover! 8) Well, I didn't exactly build it from scratch, I used manufacturers' surplus boards where possible. All obtained from the wonderful Manor Supplies. The set cost me nearly £300 if I recall correctly - not much different from buying a set. But the magazine articles paid for the set and left me some pocket money!

Back then there was only one thing to be done with 405 - get rid of it ASAP!

ppppenguin · 13th Sep 2004, 4:11 pm

Was that the PTV colour receiver? Or was that a little later?

David_Robinson · 13th Sep 2004, 4:45 pm

No, that was nothing to do with me. That was a project to build from scratch. I seem to recall it was done by Keith Cummins. My set used a field timebase/line drive board and the IF strip by Bush (RBM), all solid state. The line output (Pye, valves) and the video board (RBM) were hand built to the manufacturer's circuit and the colour decoder was a design from a large size Mullard paperback book that would probably be worth a lot if I had kept it.

I was working as an apprentice at Marconi in Chelmsford at the time, and a lot of people were building colour sets. We clubbed together to buy the major parts. I well remember a big Mullard truck turning up with I think around 15 to 20 26 " picture tubes.

I recall that the RBM IF strip had an unusual design. It had a quasi-parallel system where one channel did the luminance and the other did the chroma and sound. The theory was that you could have a deep sound notch in the luminance path, which eliminated the bane of early 625 IF's, the wiggly sound/chroma beat pattern. This was of course before the widespread use of synchronous detectors.

To use John (the editor) Reddihough's favourite word, HOWEVER, RBM's design had a fatal flaw that I only sussed years later. They had failed to eliminate the sound/luma beat in the chroma IF. Luma at 1.57MHz would beat with sound at 6MHz to give 4.43MHz. I remember noticing at the time that the cross-colour seemed worse than other sets, but I couldn't think of a reason.

7th Sep 2004, 6:08 pm	#1
ppppenguin Retired Dormant Member Join Date: Dec 2003 Location: North London, UK. Posts: 6,168	405 NTSC colour There's a possibility that Darryl may reprogram the Aurora standards converter to do 405 NTSC out. Any interest? See also: https://www.vintage-radio.net/forum/showthread.php?t=948 Last edited by Paul Stenning; 29th Dec 2004 at 3:12 pm.

7th Sep 2004, 10:04 pm	#2
evingar Octode Join Date: Oct 2003 Location: Newbury, Berkshire, UK. Posts: 1,772	Re: 405 NTSC colour Hi Jeffrey While I am (mightily!) impressed that this can be done. I am Really struggling to think of where the feature might be used. The only possibility that comes to mind is if someone has old broadcast equipment that was used in the early days of colour TV implementation. I seem to remember that NTSC 405 lines were broadcasted experimentally for a time. I believe there was a magazine article on this a while back (405 Alive?). Chris __________________ Chris

7th Sep 2004, 10:09 pm	#3
jim_beacon Retired Dormant Member Join Date: Mar 2003 Location: Bishop's Waltham, Hants, UK. Posts: 939	Re: 405 NTSC colour There are a small number of the experimental 405 NTSC sets still in existence, but only two or three, I think - can you confirm Jeffrey? Jim.

7th Sep 2004, 10:46 pm	#4
Steve_McVoy Pentode Join Date: Feb 2004 Location: Columbus, Ohio, USA Posts: 150	Re: 405 NTSC colour David Boynes is restoring one: http://www.earlytelevision.org/pye_experimental_color.html http://www.earlytelevision.org/pye_color_restoration.html

8th Sep 2004, 7:43 am	#5
ppppenguin Retired Dormant Member Join Date: Dec 2003 Location: North London, UK. Posts: 6,168	Re: 405 NTSC colour Not sure exactly how many of these experimental sets survive but probably fewer than 5.

8th Sep 2004, 8:47 am	#6
Duke_Nukem Octode Join Date: Jan 2003 Location: Birmingham, West Midlands, UK. Posts: 1,268	Re: 405 NTSC colour How many manufacturers do you rekon actually made the odd experimental set ? I assume it was really just the big boys ? Theres an interesting two-part artical in Wireless World (1956) on the Murphy one. TTFN, Jon

8th Sep 2004, 4:02 pm	#7
David_Robinson Retired Dormant Member Join Date: Feb 2004 Location: Nottingham, UK Posts: 94	Re: 405 NTSC colour I guess it wouldn't be too difficult to modify a dual standard colour set to work on 405 NTSC instead of 625 PAL. Would that make the set more authentic or less? Retune the bandpass filter and notch filter, fit a new crystal, defeat the PAL switch and shift the chroma phase by 33° - job done! Now where can I get a set?

8th Sep 2004, 5:09 pm	#8
ppppenguin Retired Dormant Member Join Date: Dec 2003 Location: North London, UK. Posts: 6,168	Re: 405 NTSC colour I don't think you need the 33 degree shift. You can consider NTSC as modulated on the U and V axes. You can modulate and demodulate on those axes. The only thing you lose is the wider I bandwidth. I believe that very few coders or sets actually use the I and Q axes with their different bandwidths.

8th Sep 2004, 7:33 pm	#9
David_Robinson Retired Dormant Member Join Date: Feb 2004 Location: Nottingham, UK Posts: 94	Re: 405 NTSC colour Yes, of course you're right. Look, it's 12 years since I worked on NTSC...

9th Sep 2004, 11:46 am	#10
Mike Phelan Dekatron Join Date: Nov 2003 Location: Near Leeds, West Yorkshire, UK Posts: 4,616	Re: 405 NTSC colour You may have to add a 'tint' control for the ref osc phase, so you can correct for lilac or puce skin-tones, that NeverTwiceSameColour was renowned for! David - thought I recognised the name - are you a fellow ex-'Television' scribe? __________________ Mike.

13th Sep 2004, 4:07 pm	#11
David_Robinson Retired Dormant Member Join Date: Feb 2004 Location: Nottingham, UK Posts: 94	Re: 405 NTSC colour Good grief, that's going back a bit! My finest hour - the March 1974 issue with my home-built colour set on the cover! 8) Well, I didn't exactly build it from scratch, I used manufacturers' surplus boards where possible. All obtained from the wonderful Manor Supplies. The set cost me nearly £300 if I recall correctly - not much different from buying a set. But the magazine articles paid for the set and left me some pocket money! Back then there was only one thing to be done with 405 - get rid of it ASAP!

13th Sep 2004, 4:11 pm	#12
ppppenguin Retired Dormant Member Join Date: Dec 2003 Location: North London, UK. Posts: 6,168	Re: 405 NTSC colour Was that the PTV colour receiver? Or was that a little later?

13th Sep 2004, 4:45 pm	#13
David_Robinson Retired Dormant Member Join Date: Feb 2004 Location: Nottingham, UK Posts: 94	Re: 405 NTSC colour No, that was nothing to do with me. That was a project to build from scratch. I seem to recall it was done by Keith Cummins. My set used a field timebase/line drive board and the IF strip by Bush (RBM), all solid state. The line output (Pye, valves) and the video board (RBM) were hand built to the manufacturer's circuit and the colour decoder was a design from a large size Mullard paperback book that would probably be worth a lot if I had kept it. I was working as an apprentice at Marconi in Chelmsford at the time, and a lot of people were building colour sets. We clubbed together to buy the major parts. I well remember a big Mullard truck turning up with I think around 15 to 20 26 " picture tubes. I recall that the RBM IF strip had an unusual design. It had a quasi-parallel system where one channel did the luminance and the other did the chroma and sound. The theory was that you could have a deep sound notch in the luminance path, which eliminated the bane of early 625 IF's, the wiggly sound/chroma beat pattern. This was of course before the widespread use of synchronous detectors. To use John (the editor) Reddihough's favourite word, HOWEVER, RBM's design had a fatal flaw that I only sussed years later. They had failed to eliminate the sound/luma beat in the chroma IF. Luma at 1.57MHz would beat with sound at 6MHz to give 4.43MHz. I remember noticing at the time that the cross-colour seemed worse than other sets, but I couldn't think of a reason.