70th anniversary of colour TV

[ppppenguin]

On Today this morning at about 0740 they had Jamie Medhurst https://www.bbc.co.uk/historyofthebbc/re...nd-the-bbc talking about the 70th anniversary of experimental colour from Alexandra Palace. Technical details sounded about right. Audio clip from "Early one morning" where there is surviving cine film. Remember that this was before videotape.

[Raditechman]

Used to watch the BBC colour tests in the 1950s on 405 lines. I belielve they were NTSC not that it mattered to me watching on a black and white Pye V4. I was very young then but used to like seeing the dot effect on greys which you got with the colour transmissions and thinking "wow must be in colour"
John

[ppppenguin]

They were indeed NTSC as there was no other system at the time. Your V4 must have had good frequency response to see the dot crawl.

The colour cameras (huge, 3x image orthicon tubes) and monitors were largely American technology adapted to 405.

[DrStrangelove]

There's a couple of 1950s 405 line colour tvs on the following site:

https://www.oldtechnology.net/colour4.html

I recall seeing a colour tv in the early 1960s on a visit to the Radio Show in Olympia.

[ppppenguin]

That's Mikey's website. I've been to his house a couple of times. He used to host meet-ups the day before NVCF. He has a lot of TVs

At the Broadcast Engineering Museum we have a similar GEC from the same period that has been modified to 625 PAL. The technology is standard early American with 21" round CRT. We haven't attempted to run it. It's on display in our reception area. We got it while clearing the house of a late Marconi engineer in east London. It only just goes through doorways. We also got a complete Marconi Mk III camera channel, a couple of astonishingly heavy 19" rack cabinets and various other kit. We think Marconi was actually an ironfoundry company that happened to do wireless etc as a sideline.

As a kid I was taken to a colour TV exhibition at Mullard House (Torrington Place, off Tottenham Court Road) where I was actually televised in colour. Must have been in 1967 at the start of the colour service. Don't remember the camera but it was probably a Philips PC60. The receivers were from many manufacturers and included the Decca CTV25 and Bush CTV25.

[Kalee20]

It must've been a super fun time to have been around!

I'm not a fan of TV... but the electronickery is fascinating... Alan Blumlein's waveform with EMI, and later the coming of colour, all shoe-horned into the same waveform, monochrome-compatible.

And of course the productionising eventually of colour CRT's, and manufacturing them at an affordable price.

[ppppenguin]

The shoehorning of colour into the monochrome signal was foretold by Mertz and Gray in their classic paper from 1934. The whole of this paper (and indeed the entire Bell System Technical Journal) used to be free to access online. There's an extract here: https://onlinelibrary.wiley.com/doi/abs/....tb00675.x They said that it should be possible to fit another TV signal into spectral gaps, but didn't mention colour. NTSC and PAL do exactly that.

If somebody described the shadowmask CRT, you might well think them mad. Yet it dominated colour TV displays for over 50 years.

[Mike Watterson]

Amazingly the beam index CRT was first demoed in about 1951, but technical problems not solved till late 1990s, when it was too late. One version used UV emission from the rear of the blue stripe and a photo detector at the single gun. However without more advanced electronics sequential frame or shadowmask was better. If the triple gun shadowmask had not been invented, or if colour had been added in 1935, then colour would have used sequential frames and an optical filter. The conceptually simple idea of a single gun beam indexed stripe phosphor CRT proved very difficult to implement.

Another early system (1924 and early 1950) was sequential frame colour. In one model the CRT was inside a drum with the colour filters. The single chip DLP projectors use a colour wheel and convert to sequential frame colour. Hence if you move your head suddenly you may see a rainbow effect.

Without a frame store any sequential frame colour system might have needed three times the bandwidth. NTSC, PAL and SECAM use a much lower chroma bandwidth (very much lower VHS) which helps in fitting the signal into the spectrum gaps.

PAL plus took advantage of the black bands of letterbox transmission of Widescreen for 4:3 to add a signal to improve "zoomed" letterbox on 16:9 screens. RTE used it for a while.

IMO Widescreen TVs and WS transmission (letterboxed or not) should never have existed till there was Digital HD.

[ppppenguin]

Some of the earliest colour displays were "triniscopes", a set of 3 CRT's with dichroic filters. They provided a display for developing NTSC colour before the shadowmask CRT was available. Earlier still, Baird tried two-colour tubes with special screens that had electron beams aimed from 2 different angles. An extension to 3 colour was proposed but I doubt it was implemented. The glassware was based on that used for mercury arc rectifiers.

The short-lived CBS colour (color?) system from 1948 used colour wheels, 405 lines and 180 fields per second. Inevitably it was totally incompatible with existing monochrome services and that was fatal.

Colour wheel sequential cameras were also used on the Apollo missions.

[DrStrangelove]

An ancient tome in the skool library showed the Baird 2 gun crt IIRC.

A strange concept.