Winter project.

[Murphyv310]

Hi.
Further improvements made today.
Only two component changes are required in the frame stage to run 25Hz so long as a 30PL1 is fitted instead of an ECL80. Details later on.

This is 180 lines showing test card "F"     

This is 240 lines showing an incorrect test card "C" with BBC2 625 lines       



I could do with two full size Test Card "C" images one stating 180 lines and the other 240 lines to load into the Multistandard Aurora memory!!

Focus could be better but I'm sure my CRT G2 volts are too high.

[Murphyv310]

Hi.
One very important thing to do tomorrow is to shroud the EHT smoothing and rectifier, also to fit three 33 meg in series as an EHT bleeder. A 0.1uf cap with 6Kv across it is lethal.

[Murphyv310]

   
Hi
I've decided that after tidying up the wiring and some small mods I'll put this project to bed.
It was a little bit silly in a way as I'd never use 240 or lower line standards with the CRT I'm using, it still flickers and the long persistence tube does nothing for entertainment value.
I will say yet again It is a reasonably easy to fit a Jelly Pot LOPT to really any monochrome TV, so if anyone has one from a 900 to 1400 these will do any 405 Line or Dual standard and if 240 or 180 lines floats your boat then give it a try.
As promised I will up load the circuit later on in the week.
Thanks to all that have looked or commented.

[BusyBee]

I loved the spirit of this, even if it took a bit of understanding!

[Murphyv310]

Thank you.
Perhaps a strange thing to do with a set but it was a scrapper to be fair.
I'm still continuing but not likely I'll do an awful lot more. I'd like to get it nice and tidy so it can be switched on for anyone to have a look. 
I just might carry on if someone has an idea how to do 120 line mechanical syncs.

[`FRANK.C]

Hi Trevor
Well done to get such good results. Scanning at low line speeds cant be easy.
I would think very few have seen 240 lines, I for one would love to see 240 lines in action and I am sure that many more would as well.
I had thought a longer persistence tube would be the answer to the flickering but now we know that  isn't the case.

Frank

[Murphyv310]

Thanks Frank.
I was quite baffled why the flicker is so noticeable especially as with moving images are so blurred. I tried to watch football on 180 lines yesterday and it was impossible to follow the action.
I suppose this has just been an experiment.
It now begs the question if Baird had some special tube that was able to reduce the flicker but be less blurred on moving images?

[ppppenguin]

The question of 25Hz flicker has been raised more than once. There are good reasons why it would have been less objectionable in 1936 than it is now. The first is that your central vision is not very sensitive to flicker but peripheral vision is. So a small screen viewed from a fair distance will seem less flickery. Another reason is brightness - modern pictures, even on a good 1950s set, are rather brighter than in 1936. Flicker is more visible at higher brightnesses. Finally I think we just got used to it. Many years ago I didn't notice flicker. Then I started doing some investigation of flicker as part of a research project and found myself increasingly sensitive. Now I'm used to LCD screens which don't flicker at all, even at low refresh rates. If I see an old CRT computer monitor at 60Hz refresh it's horrible. Of course you're sitting cloes to a PC so peripheral vision flicker matters more than with a TV.

[Murphyv310]

Good point Jeffrey.
I think tomorrow I'll run the set up on a fairly low brightness level and get further away from it and see if the flicker is less objectionable.

[peter scott]

Well it's still pretty objectionable on my rather dim 901 even when viewed from a distance to minimise any peripheral vision sensitivity. It would be great to see it displayed on an early Baird set.

Peter