Why did 405 look so good?

[colly0410]

From what I can remember 405 lines TV always looked good; bright, sharp & with good contrast. In theory though it shouldn't have looked as good as it did, what with lack of lines, 2.5 to 3 Mhz bandwidth, mean level AGC. OK you had car ignition/electrical/sporadic E interference on band 1 but you can't blame 405 for that as it was the same when I was in Barcelona & Miami only in colour. On a dual standard set 405 often looked brighter & better than 625. My Canadian cousin said our pictures were better than their 525 ones. Never seen an 819 picture so can't comment on them..

[pwdrive]

What most folks classed as good contrast was a picture with the wrong contrast from what I remember, local/distant flat out, contrast flat out, brightness reduced to stop the tube flaring/going out of focus etc.

Lawrence.

[ppppenguin]

Apart from poor UHF performance of some dual standard sets there's a psychological or perceptional reason. If you can see the lines sharply defined you tend to think the picture is sharp. Even if it isn't.

[peter scott]

Given the switching from positive to negative modulation perhaps it was the effects of non-linearity in the RF, IF and detector characteristics on the gamma of the picture presented on the screen.

Peter

[peter scott]

Duplicated post.

[Refugee]

Surely the write speed to the tube face was faster with 625 so there was less time for the phosphor to take the electron beam current and light up. The difference in write speed is close to 50%.
Try it with a CRT scope and you will see an extreme example as you change the time base speed. You need to turn the brightness up.

[Murphyv310]

Hi.
Many of the engineers in broadcasting blamed the dual standard sets for being rubbish on UHF, granted the valve tuners were a disaster but it was odd that in November 1969 when we duplicated the UHF pictures suddenly came to life. Even now those with dual standard sets in their collection report how well they work on 625.
I have to say though a well set up 405 line picture does take a lot of beating

[Murphyv310]

Surely the write speed to the tube face was faster with 625 so there was less time for the phosphor to take the electron beam current and light up. The difference in write speed is close to 50%.
Try it with a CRT scope and you will see an extreme example as you change the time base speed. You need to turn the brightness up.

A fair point but 819 lines would have been grim by your reckoning with an even faster scan speed, the closer the line spacing the higher the subjective brightness, as you are scanning more phosphors.
Try increasing the height, the increase in line spacing reduces perceived brightness, reducing height give the opposite effect.

[Terry]

Around 1960/61 when we were debating whether to stick with 405 or go for 625, somebody from one of the US networks told a conference that we should definitely go for 625 but then added that he thought our 405 line pictures were better than their 525 line ones!

One of our college lecturers said that a major difference between UK and US practice was that our broadcasters leased their camera tubes and would get the manufacturer to replace any that started giving trouble whereas, in the US, they bought the tubes outright and, so long as they produced something vaguely resembling a picture, they remained in service!

Certainly, my early memories of US pictures - only the electronically converted ones, obviously! - were of considerable inferior quality.

[Crackle]

As far as I can remember the 405 tv's were not so good in daylight, especially with direct sunlight on them, but they were excellent at night.
Mike