Seeing colour in a B&W film..

[Brian Gaff]

Was this the famous OXO cartoon? If it was then all most saw was an ever changing patterning effect as if something was interfereing with some parts of the pictures. Brian

[Harry Bloomfield]

Brian Gaff pretended :

The only parts of the film which exhibited any colour at all, was the Christmas tree, when the tree was in shot it was also a very slight effect almost barely noticeable to me. It was so slight I paid extra attention to it in later appearances, to see if I might be imagining it. It was similar to the modern effect they use, where a single item is coloured deliberately in a B&W film, but I doubt such would have / could have been done in 1966 - had it been deliberate, no doubt it would have been a more definite green.

[tabbypurr]

It still has uses, or did in the B&W days, but only where the absolute colour value doesn't matter a hoot, which of course is mostly not the case.

NT

[tabbypurr]

First generation CRT sets used a mains transformer to provide EHT for the C RT. A red pygmy lamp was fitted in series with the mains side for short pro tection. There's an old story out there about a woman that phoned Ally Pall y to congratulate them on the lovely shades of red & pink in the picture on ly to be told she should switch it off before it caught fire.

The EHT was deadly on these sets.

NT

[Bill Wright]

They used to be something called a colour killer that locked the telly to monochrome when a monochrome prog was on. When it didn't work the picture would have spurious colours, usually flashing. It was most annoying.

Bill

[NY]

I presume this was a transformer that had mains on the primary and EHT on the secondary, needing only a rectifier and smoothing circuitry to give the EHT for the tube, whereas modern CRTs used a relatively low voltage (maybe mains), that was rectified and then multiplied by a ladder rectifier/capacitor stack so the full EHT was achieved after several mains cycles - one to charge each capacitor in the ladder.

Isn't EHT *always* deadly? If a current-limiting resistor was fitted to reduce the severity of an electric shock from the several thousand volts of EHT, wouldn't it prevent enough current flowing to drive the CRT?

[NY]

I realise that broadcasters used to turn off the colour carrier when a monochrome programme was broadcast, though I imagine towards the end of analogue TV, broadcast equipment might start to protest if the CSC was ever not present.

For digital, I'm surprised that the source material direct from the telecine doesn't have the three components set to equal values, long before it gets as far as the broadcast equipment.

Talking Pictures TV shows a lot of B&W material and there is often a colour cast - most noticeable when they change from one film to a trailer for another at an advert break.

[Roger Hayter]

I am sure the mains ones had a transformer with a single digit kV output and used a voltage multiplier (the names of Cockcroft and Walton spring to mind). The difference was that the later ones used a transformer (driven by a power valve) at line frequency, about 10kHz originally (well, 10kc/s originally). This more easily limited the maximum power avaliable from the transformer. I would guess that the mains transformer secondary was more lethal than the higher voltage output of the voltage multiplier as more current would be available. The EHT is more likely to cauterise the skin than to electrocute, especially at the higher frequency. That was certainly the result the one time I put a finger too near the anode of an HF output valve operating at about

1.5kV.

It is said to take tens of milliamps to electrocute, and B & W TVs would probably not produce this amount of EHT current.

[tabbypurr]

no connection at all

NT

[tabbypurr]

yes except i doubt they had smoothing, the CRT anode has significant capacitance.

no, for decades TVs used an EHT winding on the LOPTF that was fed to a tripler. I've never seen one use a mains fed large value multipler stack, and doubt it would work.

no, contact with TV EHT was survivable, if not fun. Not so for early sets though.

I've never seen that done.

NT

[Dave Plowman (News)]

Which isn't going to make any difference on a monochrome telecine. If using a colour telecine for mono film you set the greyscale to give true B&W.

[Dave Plowman (News)]

All down to costs. Everyone knows digital is perfect so can be used with no human intervention to check things.

If 'they' can't get something like audio levels somewhere near close when doing a transfer, not much hope for far more complicated pictures.

[Terry Casey]

I'm fairly certain that it was simply a very high voltage secondary winding - no need for a multiplier.

The EHT was derived from an overwind on the Line Output Transformer which coupled the output stage to the scan coils.

The same principle was used in early colour sets (where the EHT was 25kV) but later sets had a lower voltage overwind and a tripler.

Certainly - if my experiences are anything to go by! But I wouldn't take any chances with a colour set.

EHT on a monochrome set only needs to supply a few tens of microamps but colour tubes - particularly the early ones - used the shadowmark principle whereby the three angled electron beams converged on the shadowmask mpounted behing the face plate. Small holes permitted the electrons to pass though the mask where they started to diverge again so that each beam only hit its corresponding phosphor to produce the three primary colours. A lot of the energy was absorbed by the steel shadow mask so a cuurent of up to 1.5mA was required and that, at 25kV, is lethal!

[Terry Casey]

It will be, in the same way that analogue scanners and cameras were.

However, to produce the monochrome part of the picture, the three signals have to be combined in exactly the correct ratio which is 59% Green, 30% Red and 11% Blue.

TV signals were produced in digital form for years before DSO so the analogue signals produced from them needed to be in exactly the same proportions to avoid upsetting the colour balance.

[tabbypurr]

it wouldn't make any sense to implement a valve multiplier chain.

NT

[charles]

EY51, as I recall, in Pye monchrome studio monitors

[Terry Casey]

Yes, three of them!

They would each, of course, have needed an individual insulated heater winding!

[tabbypurr]

Never seen anything like that in a domestic set, very cost inefficient indeed. Why would they do it?

NT

[Harry Bloomfield]

I would expect that part of the process to be automated, adjusted automatically for colour cast on a B&W film.

[charles]

Ata guess - for stability of the picture.