Revisiting an old topic - Adding DC Restoration to a 1950s TV

[maxhifi]

I think the human eye sees a far greater range of contrast than vintage TV sets can display. In old TV shows, it seemed common to light up night scenes quite brightly by today's standards in order to get any image on the film, but the more modern trend seems to be a huge range between the brightest and darkest scenes. I would say it is almost analogous to the difference between the noise floor and the loudest possible recording on a 78RPM record versus a digital recording.

This large contrast range really asks a lot of old TVs, and that's why I wanted to try and do something to improve the Marconi, if only slightly. Better yet it seems to me would be some kind of signal processing to dynamically compress the contrast range, like say using a variable mu tube as the video amplifier, to have the effect of turning the contrast down in dark scenes, but I'm afraid I'm not smart enough to design that.

[Kevin Kuehn]

Well of course the contrast on old sets was/is limited to whatever the CRT face reflects in any given ambient lighting. That's the main reason modern flat screens can produce such apparent contrast. But in IMO it's pushed over the edge, to the point of now being an effect more so than anything you'd see inside or outdoors in natural lighting. Keeping in mind that everyone's eyes aren't calibrated the same, not anymore that our ears are. I've met a few folks that don't see color, or so they say.

[maxhifi]

Originally Posted by Kevin Kuehn

Well of course the contrast on old sets was/is limited to whatever the CRT face reflects in any given ambient lighting. That's the main reason modern flat screens can produce such apparent contrast. But in IMO it's pushed over the edge, to the point of now being an effect more so than anything you'd see inside or outdoors in natural lighting. Keeping in mind that everyone's eyes aren't calibrated the same, not anymore that our ears are. I've met a few folks that don't see color, or so they say.

There have been a few shows which give my CRT based Runco HDTV projector fits, because the night scenes are so dark, that if I adjust contrast to suit them, then the picture looks horrible on bright scenes. What tripped up the Marconi was concert videos where they alternate between dark very bright. The DC restoration circuit seems to help these.

I agree though, it is kind of pushing things too far, but unfortunately I have no influence over what sort of signal the TV gets. I actually use my vintage sets for 100% of TV watching, simply because I like them. I can't convince the family to live in black and white though, so the main living room set is a CTC38.

[Kevin Kuehn]

Don't get me wrong, I'm not suggesting the DC restorer isn't helping out on your Marconi. I was simply pointing out that there's a multitude of things than can compound the situation. I've watched modern over the air TV from the S video luminance output, through my Blonder Tongue agile modulator, which even then the contrast can seem very washed out, and this on a set with DC coupling from detector to CRT. It's not solely a mater of DC component. [edit] well it might be a matter of DC component gone missing from some point in the signal chain, but not necessarily within the vintage TV.

[maxhifi]

Originally Posted by Kevin Kuehn

Don't get me wrong, I'm not suggesting the DC restorer isn't helping out on your Marconi. I was simply pointing out that there's a multitude of things than can compound the situation. I've watched modern over the air TV from the S video luminance output, through my Blonder Tongue agile modulator, which even then the contrast can seem very washed out, and this on a set with DC coupling from detector to CRT. It's not solely a mater of DC component.

I'm not thinking it is a miracle solution, but rather a situation where every little bit helps. The Marconi is never going to perform like something newer, but if three little $0.10 parts can make it 10% better then why not? The elephant in the room with the Marconi is that the CRT is on the weak side, which already diminishes the contrast range. Which reminds me I ought to get my blonder tongue modulator up and running!