Re: CRTs on Ebay
Don Black <donald_black@...>
Thanks Craig, interesting comments. Actually I'm in Australia but worked on some C1958 Marconi prototype colour equipment. Very useful experience. The PAL is rock solid by comparison.
Our colour service started in March 1975 using PAL. For a few years before that a few of us were watching some colour programs from tapes from the UK and England. The local signal processors stripped off all the colour burst used to lock the chroma circuits but with PAL you can recover lock signals from the chroma which wasn't filtered out. Philips hawked some prototype sets around the trade in the late sixties (trying to push colour introduction I think) and included a little chroma lock board to allow users to watch the program. It recovered the lock signal and just injected it into the chroma oscillator as a trigger but apart from just managing lock on a stable signal generator I never saw it successfully lock to an off-air program (It might have worked on a properly stabilised program?). I thought it would be better with an AFC phase locked loop and built up a few boards using it. They worked far better than I hoped and would always lock solidly to the weakest chroma. The quality off the tapes varied from excellent to colour snow but it always locked right up. So for a few years we watched just about anything that moved in colour. I've still got a board kicking around somewhere.
I believe when they were developing what became he NTSC colour system in the US it was suggested it would be advantageous to switch one colour signal phase on alternative lines (same as PAL) but it wasn't considered worth it and didn't happen. The one line delay line really makes the PAL system and I guess there wouldn't have been a cheap 64µs delay line available. It was the development of the acoustic glass delay line that really made it viable. The same delay was later used in VCRs for dropout compensation. There is still some advantage of the PAL system without a delay line, the eye averages the colour errors but gives the Venetian blind effect.
On 13-Jan-14 12:36 AM, Craig Sawyers wrote: