I have been watching an occasional old film on 81 (Talking Pictures).

This morning there was a short BFI B&W kids film on (The Christmas
Tree), from 1966, with kids involved in journey taking a Christmas tree
to London. Rather oddly and despite it being a B&W film, the tree's
foliage showed up quite faintly as green. None of the grass, nor the
other trees showed as even slightly green. All rather puzzling, but I
remember a TV experiment from way back, where they tested B&W TV's to
hint at showing some colour. Anyone remember it?

I like watching some of these older low budget films, for the quiet
roads and vehicles from the early days of my motoring career.

In article ,
Harry Bloomfield wrote:
This morning there was a short BFI B&W kids film on (The Christmas
Tree), from 1966, with kids involved in journey taking a Christmas tree
to London. Rather oddly and despite it being a B&W film, the tree's
foliage showed up quite faintly as green. None of the grass, nor the
other trees showed as even slightly green. All rather puzzling, but I
remember a TV experiment from way back, where they tested B&W TV's to
hint at showing some colour. Anyone remember it?

A B&W TV can't show colour - other than that of its phosphor. Assuming you
are talking old CRT sets - not sure I've ever seen a B&W LDC, other than
tiny ones.

It might be possible to confuse the eye into thinking a part of the
picture is in colour by using some sort of pattern. But that isn't the set
producing colour.

--
*A chicken crossing the road is poultry in motion.*

Dave Plowman London SW
To e-mail, change noise into sound.

On Sun, 31 Dec 2017 11:58:41 +0000, Harry Bloomfield wrote:

All rather puzzling, but I remember a TV
experiment from way back, where they tested B&W TV's to hint at showing
some colour. Anyone remember it?

Yes, it was shown that certain flicker rates caused the brain to 'see'
colour. An OXO commercial was shown and some people saw the gravy as
brown and some as purple. It didn't catch on.

--
TOJ.

Dave Plowman (News) pretended :
A B&W TV can't show colour - other than that of its phosphor. Assuming you
are talking old CRT sets - not sure I've ever seen a B&W LDC, other than
tiny ones.

The BBC conducted some experiments in the 1960's, I think Tomorrow's
World might have been involved. Then of course all TV's were CRT, but I
did see a slight hint of colour, on a B&W CRT. Some saw nothing as I
remember.

In article ,
The Other John wrote:
On Sun, 31 Dec 2017 11:58:41 +0000, Harry Bloomfield wrote:

All rather puzzling, but I remember a TV
experiment from way back, where they tested B&W TV's to hint at showing
some colour. Anyone remember it?

Yes, it was shown that certain flicker rates caused the brain to 'see'
colour. An OXO commercial was shown and some people saw the gravy as
brown and some as purple. It didn't catch on.

Tomorrows World showed something like that in the late '60s. Sadly, the
film was American and intended to be shown at 24fps. In the UK showing it
25fps gave completely different results to the script

--
from KT24 in Surrey, England

On Sunday, 31 December 2017 12:20:07 UTC, Dave Plowman (News) wrote:
In article ,
Harry Bloomfield wrote:

This morning there was a short BFI B&W kids film on (The Christmas
Tree), from 1966, with kids involved in journey taking a Christmas tree
to London. Rather oddly and despite it being a B&W film, the tree's
foliage showed up quite faintly as green. None of the grass, nor the
other trees showed as even slightly green. All rather puzzling, but I
remember a TV experiment from way back, where they tested B&W TV's to
hint at showing some colour. Anyone remember it?

A B&W TV can't show colour - other than that of its phosphor. Assuming you
are talking old CRT sets

Early CRT TVs were known to produce a pink picture when the EHT partially shorted, causing the current limiting red lamp to light behind the CRT.


NT

"Harry Bloomfield" wrote in message
news
I have been watching an occasional old film on 81 (Talking Pictures).

This morning there was a short BFI B&W kids film on (The Christmas Tree), from 1966,
with kids involved in journey taking a Christmas tree to London. Rather oddly and
despite it being a B&W film, the tree's foliage showed up quite faintly as green. None
of the grass, nor the other trees showed as even slightly green.

I sometimes experience lemon tinted whites when watching B&W
films on a modern TV, say when a character is wearing a
white shirt - while all the other whites show up ok. Also sometimes
the sky has a distinct lemon or mauve tinge.

There's a way around it by altering the settings although offhand
I can't remember what it is. ISTR it may also be affected by the
viewing angle.


michael adams

....

In article ,
The Other John wrote:
On Sun, 31 Dec 2017 11:58:41 +0000, Harry Bloomfield wrote:

All rather puzzling, but I remember a TV
experiment from way back, where they tested B&W TV's to hint at showing
some colour. Anyone remember it?

Yes, it was shown that certain flicker rates caused the brain to 'see'
colour. An OXO commercial was shown and some people saw the gravy as
brown and some as purple. It didn't catch on.

Quite. Fooling the brain into thinking there is colour is an interesting
trick. But unless consistent for everyone, a bit pointless.

--
*How do you tell when you run out of invisible ink? *

Dave Plowman London SW
To e-mail, change noise into sound.

In article ,
wrote:
A B&W TV can't show colour - other than that of its phosphor. Assuming
you are talking old CRT sets

Early CRT TVs were known to produce a pink picture when the EHT
partially shorted, causing the current limiting red lamp to light behind
the CRT.

How early are you talking about? I've never heard of that one.

--
*Heart attacks... God's revenge for eating his animal friends

Dave Plowman London SW
To e-mail, change noise into sound.

"Harry Bloomfield" wrote in message
news
Dave Plowman (News) pretended :
A B&W TV can't show colour - other than that of its phosphor. Assuming
you
are talking old CRT sets - not sure I've ever seen a B&W LDC, other than
tiny ones.

The BBC conducted some experiments in the 1960's, I think Tomorrow's World
might have been involved. Then of course all TV's were CRT, but I did see
a slight hint of colour, on a B&W CRT. Some saw nothing as I remember.

Yes indeed. It used different mark/space ratios of flashing to make the
effect. As a boy I made a spinning disc optical illusion which has four
circular tracks with different ratios. There is a youtube demo of it he
https://youtu.be/hf3KTsRRPLs (fast forward to midway to skip the prologue).
--
Dave W

On 31/12/17 11:58, Harry Bloomfield wrote:
I have been watching an occasional old film on 81 (Talking Pictures).

This morning there was a short BFI B&W kids film on (The Christmas
Tree), from 1966, with kids involved in journey taking a Christmas tree
to London. Rather oddly and despite it being a B&W film, the tree's
foliage showed up quite faintly as green. None of the grass, nor the
other trees showed as even slightly green. All rather puzzling, but I
remember a TV experiment from way back, where they tested B&W TV's to
hint at showing some colour. Anyone remember it?

I like watching some of these older low budget films, for the quiet
roads and vehicles from the early days of my motoring career.

Others have talked about the psychological experiments with B&W TV but
it crosses my mind that there could be lots of reasons why a solid-state
colour TV has difficulty interpreting black, white and only greyscale in
between, ranging from the set, the method of transmission and even down
to the transfer from celluloid to digital in the first place.

Going back even further, the original B&W film stock may not have been
true black on a clear-as-water celluloid base and different chemical
processes can give different results. Guess who was given a copy of "The
Book of Alternative Photographic Processes (Third Edition)" for Christmas?

Nick

On Sun, 31 Dec 2017 12:35:38 GMT, Harry Bloomfield
wrote:

Dave Plowman (News) pretended :
A B&W TV can't show colour - other than that of its phosphor. Assuming you
are talking old CRT sets - not sure I've ever seen a B&W LDC, other than
tiny ones.

The BBC conducted some experiments in the 1960's, I think Tomorrow's
World might have been involved. Then of course all TV's were CRT, but I
did see a slight hint of colour, on a B&W CRT. Some saw nothing as I
remember.

I think I remember it, I couldn't see any effect but there always some
like my mum who reckoned they could. Did it involve in strobing the
image at certain rate? There was a craze for looking at hidden images
amongst a load of squiggles printed on paper about 20-30 years ago, I
could never see those either but others found them quickly, OTOH as
the printed pattern looked a bit like the ones sometimes printed on
paper surrounding sensitive information such as a salary slip and we
convinced a colleague that the within the pattern the company trade
mark could be seen and he then announced he could see it I've been a
bit skeptical as to how many were genuine.

BBC 4 returned to the subject in more recent times.
https://www.youtube.com/watch?v=3P8q_dCU3RI

G.Harman

On Sun, 31 Dec 2017 13:46:52 +0000 (GMT), "Dave Plowman (News)"
coalesced the vapors of human experience into a
viable and meaningful comprehension...

In article ,
wrote:
A B&W TV can't show colour - other than that of its phosphor. Assuming
you are talking old CRT sets

Early CRT TVs were known to produce a pink picture when the EHT
partially shorted, causing the current limiting red lamp to light behind
the CRT.

How early are you talking about? I've never heard of that one.

Not too sure myself, but on balance he is probably referring to a
so-called "Barretter"
https://en.wikipedia.org/wiki/Iron-hydrogen_resistor
--

Graham.
%Profound_observation%

"Harry Bloomfield" wrote in message
news
Dave Plowman (News) pretended :
A B&W TV can't show colour - other than that of its phosphor. Assuming
you
are talking old CRT sets - not sure I've ever seen a B&W LDC, other than
tiny ones.

The BBC conducted some experiments in the 1960's, I think Tomorrow's World
might have been involved. Then of course all TV's were CRT, but I did see
a slight hint of colour, on a B&W CRT. Some saw nothing as I remember.

I don't remember seeing it when it was originally broadcast. but I've seen a
Youtube video of that item on the programme (it showed a drinks can with
different "colours" on different parts of the can) and I saw a pattern, but
no hint of colour whatsoever. It's possible that modern technology was
hiding the effect: a) LCD screen rather than CRT, b) progressive scan rather
than interlaced, c) it may have been a film recording of the CRT screen,
rather than videotape, which would have destroyed the interlaced scan and
altered the gamma of the image.

"Dave W" wrote in message
news

"Harry Bloomfield" wrote in message
news
Dave Plowman (News) pretended :
A B&W TV can't show colour - other than that of its phosphor. Assuming
you
are talking old CRT sets - not sure I've ever seen a B&W LDC, other than
tiny ones.

The BBC conducted some experiments in the 1960's, I think Tomorrow's
World might have been involved. Then of course all TV's were CRT, but I
did see a slight hint of colour, on a B&W CRT. Some saw nothing as I
remember.

Yes indeed. It used different mark/space ratios of flashing to make the
effect. As a boy I made a spinning disc optical illusion which has four
circular tracks with different ratios. There is a youtube demo of it he
https://youtu.be/hf3KTsRRPLs (fast forward to midway to skip the
prologue).

I can't seen any hint of colour in the four different circles. They are
different shades of grey, dependent on the differing mark:space ratios, and
there is a quarter-circle sector that rotates (beating between rotational
rate and video scanning rate), but no colour whatsoever.

Evidently I'm one of the people who can't see the effect. :-(

"Chris Hogg" wrote in message
...
http://dailym.ai/1YeTTF6

also https://www.youtube.com/watch?v=3P8q_dCU3RI

That's a totally different effect: the eye sees colours (they are a negative
of the correct colours) and the eye/brain tires of seeing those colours so
when a black and white image is seen, the colour sensitivity of the eye
varies for different parts of the image so the eye sees a hint of the
correct colours.

The one that TW demonstrated used strobing or patterning to tire some of the
cones more than others in the eye, so as to achieve that same goal of
varying colour sensitivity of the eye.

"michael adams" wrote in message
news

"Harry Bloomfield" wrote in message
news
I have been watching an occasional old film on 81 (Talking Pictures).

This morning there was a short BFI B&W kids film on (The Christmas Tree),
from 1966, with kids involved in journey taking a Christmas tree to
London. Rather oddly and despite it being a B&W film, the tree's foliage
showed up quite faintly as green. None of the grass, nor the other trees
showed as even slightly green.

I sometimes experience lemon tinted whites when watching B&W
films on a modern TV, say when a character is wearing a
white shirt - while all the other whites show up ok. Also sometimes
the sky has a distinct lemon or mauve tinge.

Another variable throw into the mix: not all black and white films on TV are
the same shade. The film base may develop a slight colour tint as it ages,
which leads to greys that may be very pale mauve or very pale green. You'd
think that when B&W films were transmitted on TV, they would set R=G=B so as
to achieve pure, untinted B&W irrespective of the colour of the original
film.

Well so many issues here. I suspect if you had been watching it on a film
projector you would not see any colour. What this may show is shortcomings
in the digital technology or the way the three pixels of rGB affect ones
individual eye and whether persistence of vision is greater on one of them
for you, or indeed the actual pixel is on for longer.
Back in the old days of analogue when I could see a bit I could get all
sorts of strange effects due to inaccuracies in both the eye and the shadow
mask of the tube and the registration of the colours.

If its derived from film there is that added issue of the frame speed vs the
scanning speed and frame rate that it ends in and when it was converted and
how. Many say that some old films are too contrasty, ie soot and whitewash
effect blurring out detail in highlights or lowlights, all of which can
upset colour balance of the eye. So I'm not surprised that some see such
things but I don't think in these cases its deliberate. Of course it has
been all the rage in and around the 90s to artificially colour black and
white films by doing several frames in a sequence and then using 'tweening'
software to interpret the rest of the shot to make it supposedly look real.
Most who have seen these say that cartoons are OK but live action can take
on the dream like look as the hues are subtly incorrect at times and of
course if anything appears in a shot that has not been given a colour or
cannot be tracked all sorts of odd things used to occur!

Brian

--
----- -
This newsgroup posting comes to you directly from...
The Sofa of Brian Gaff...

Blind user, so no pictures please!
"Harry Bloomfield" wrote in message
news
I have been watching an occasional old film on 81 (Talking Pictures).

This morning there was a short BFI B&W kids film on (The Christmas Tree),
from 1966, with kids involved in journey taking a Christmas tree to
London. Rather oddly and despite it being a B&W film, the tree's foliage
showed up quite faintly as green. None of the grass, nor the other trees
showed as even slightly green. All rather puzzling, but I remember a TV
experiment from way back, where they tested B&W TV's to hint at showing
some colour. Anyone remember it?

I like watching some of these older low budget films, for the quiet roads
and vehicles from the early days of my motoring career.

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

--
----- -
This newsgroup posting comes to you directly from...
The Sofa of Brian Gaff...

Blind user, so no pictures please!
"Harry Bloomfield" wrote in message
news
Dave Plowman (News) pretended :
A B&W TV can't show colour - other than that of its phosphor. Assuming
you
are talking old CRT sets - not sure I've ever seen a B&W LDC, other than
tiny ones.

The BBC conducted some experiments in the 1960's, I think Tomorrow's World
might have been involved. Then of course all TV's were CRT, but I did see
a slight hint of colour, on a B&W CRT. Some saw nothing as I remember.

Brian Gaff pretended :
If its derived from film there is that added issue of the frame speed vs the
scanning speed and frame rate that it ends in and when it was converted and
how. Many say that some old films are too contrasty, ie soot and whitewash
effect blurring out detail in highlights or lowlights, all of which can upset
colour balance of the eye. So I'm not surprised that some see such things but
I don't think in these cases its deliberate. Of course it has been

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.

On Sunday, 31 December 2017 13:45:03 UTC, Dave Plowman (News) wrote:
In article ,
The Other John wrote:
On Sun, 31 Dec 2017 11:58:41 +0000, Harry Bloomfield wrote:

All rather puzzling, but I remember a TV
experiment from way back, where they tested B&W TV's to hint at showing
some colour. Anyone remember it?

Yes, it was shown that certain flicker rates caused the brain to 'see'
colour. An OXO commercial was shown and some people saw the gravy as
brown and some as purple. It didn't catch on.

Quite. Fooling the brain into thinking there is colour is an interesting
trick. But unless consistent for everyone, a bit pointless.

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

On Sunday, 31 December 2017 13:55:06 UTC, Dave Plowman (News) wrote:
In article ,
tabbypurr wrote:

A B&W TV can't show colour - other than that of its phosphor. Assuming
you are talking old CRT sets

Early CRT TVs were known to produce a pink picture when the EHT
partially shorted, causing the current limiting red lamp to light behind
the CRT.

How early are you talking about? I've never heard of that one.

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

The EHT was deadly on these sets.


NT

On 31/12/2017 17:46, NY wrote:

Another variable throw into the mix: not all black and white films on TV
are the same shade. The film base may develop a slight colour tint as it
ages, which leads to greys that may be very pale mauve or very pale
green. You'd think that when B&W films were transmitted on TV, they
would set R=G=B so as to achieve pure, untinted B&W irrespective of the
colour of the original film.

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

wrote in message
...
On Sunday, 31 December 2017 13:55:06 UTC, Dave Plowman (News) wrote:
In article ,
tabbypurr wrote:

A B&W TV can't show colour - other than that of its phosphor.
Assuming
you are talking old CRT sets

Early CRT TVs were known to produce a pink picture when the EHT
partially shorted, causing the current limiting red lamp to light
behind
the CRT.

How early are you talking about? I've never heard of that one.

First generation CRT sets used a mains transformer to provide EHT for the
CRT.

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.

A red pygmy lamp was fitted in series with the mains side for short
protection. There's an old story out there about a woman that phoned Ally
Pally to congratulate them on the lovely shades of red & pink in the
picture only to be told she should switch it off before it caught fire.

The EHT was deadly on these sets.

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?

"Bill Wright" wrote in message
news
On 31/12/2017 17:46, NY wrote:

Another variable throw into the mix: not all black and white films on TV
are the same shade. The film base may develop a slight colour tint as it
ages, which leads to greys that may be very pale mauve or very pale
green. You'd think that when B&W films were transmitted on TV, they would
set R=G=B so as to achieve pure, untinted B&W irrespective of the colour
of the original film.

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.

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.

NY wrote:

wrote in message
...
On Sunday, 31 December 2017 13:55:06 UTC, Dave Plowman (News) wrote:
In article ,
tabbypurr wrote:

A B&W TV can't show colour - other than that of its phosphor.
Assuming
you are talking old CRT sets

Early CRT TVs were known to produce a pink picture when the EHT
partially shorted, causing the current limiting red lamp to light
behind
the CRT.

How early are you talking about? I've never heard of that one.

First generation CRT sets used a mains transformer to provide EHT for the
CRT.

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.

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.






A red pygmy lamp was fitted in series with the mains side for short
protection. There's an old story out there about a woman that phoned Ally
Pally to congratulate them on the lovely shades of red & pink in the
picture only to be told she should switch it off before it caught fire.

The EHT was deadly on these sets.

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?

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

--

Roger Hayter

"NY" wrote in message
...
wrote in message
...
On Sunday, 31 December 2017 13:55:06 UTC, Dave Plowman (News) wrote:
In article ,
tabbypurr wrote:

A B&W TV can't show colour - other than that of its phosphor.
Assuming
you are talking old CRT sets

Early CRT TVs were known to produce a pink picture when the EHT
partially shorted, causing the current limiting red lamp to light
behind
the CRT.

How early are you talking about? I've never heard of that one.

First generation CRT sets used a mains transformer to provide EHT for the
CRT.

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.

A red pygmy lamp was fitted in series with the mains side for short
protection. There's an old story out there about a woman that phoned Ally
Pally to congratulate them on the lovely shades of red & pink in the
picture only to be told she should switch it off before it caught fire.

The EHT was deadly on these sets.

Isn't EHT *always* deadly?

Nope, electric fences arent.

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?

Nope the current isnt that high.

On Sunday, 31 December 2017 16:38:30 UTC, Graham. wrote:
On Sun, 31 Dec 2017 13:46:52 +0000 (GMT), "Dave Plowman (News)"
coalesced the vapors of human experience into a
viable and meaningful comprehension...
In article ,
tabbypurr wrote:

A B&W TV can't show colour - other than that of its phosphor. Assuming
you are talking old CRT sets

Early CRT TVs were known to produce a pink picture when the EHT
partially shorted, causing the current limiting red lamp to light behind
the CRT.

How early are you talking about? I've never heard of that one.

Not too sure myself, but on balance he is probably referring to a
so-called "Barretter"
https://en.wikipedia.org/wiki/Iron-hydrogen_resistor

no connection at all


NT

On Sunday, 31 December 2017 21:00:14 UTC, NY wrote:
tabbypurr@ wrote in message
...
On Sunday, 31 December 2017 13:55:06 UTC, Dave Plowman (News) wrote:
In article ,
tabbypurr wrote:

A B&W TV can't show colour - other than that of its phosphor.
Assuming
you are talking old CRT sets

Early CRT TVs were known to produce a pink picture when the EHT
partially shorted, causing the current limiting red lamp to light
behind
the CRT.

How early are you talking about? I've never heard of that one.

First generation CRT sets used a mains transformer to provide EHT for the
CRT.

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,

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

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.

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.


A red pygmy lamp was fitted in series with the mains side for short
protection. There's an old story out there about a woman that phoned Ally
Pally to congratulate them on the lovely shades of red & pink in the
picture only to be told she should switch it off before it caught fire.

The EHT was deadly on these sets.

Isn't EHT *always* deadly?

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

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?

I've never seen that done.


NT

In article ,
Nick Odell wrote:
Going back even further, the original B&W film stock may not have been
true black on a clear-as-water celluloid base and different chemical
processes can give different results. Guess who was given a copy of "The
Book of Alternative Photographic Processes (Third Edition)" for
Christmas?

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.

--
*Never underestimate the power of stupid people in large groups.

Dave Plowman London SW
To e-mail, change noise into sound.

In article ,
NY wrote:
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.

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.

--
*If at first you don't succeed, try management *

Dave Plowman London SW
To e-mail, change noise into sound.

In article ,
says...


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).

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

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.

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.


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

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

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In article
,
says...


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.


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.

--

Terry

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On Monday, 1 January 2018 14:27:57 UTC, Terry Casey wrote:
In article ,
says...


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).

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

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


NT

In article ,
wrote:
On Monday, 1 January 2018 14:27:57 UTC, Terry Casey wrote:
In article ,
says...


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).

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

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


EY51, as I recall, in Pye monchrome studio monitors

--
from KT24 in Surrey, England

In article ,
says...

In article ,
wrote:
On Monday, 1 January 2018 14:27:57 UTC, Terry Casey wrote:
In article ,
says...


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).

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

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


EY51, as I recall, in Pye monchrome studio monitors

Yes, three of them!

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

--

Terry

---
This email has been checked for viruses by AVG.
http://www.avg.com

On Monday, 1 January 2018 17:15:22 UTC, Terry Casey wrote:
In article ,
says...
In article ,
tabbypurr wrote:
On Monday, 1 January 2018 14:27:57 UTC, Terry Casey wrote:
In article ,
says...


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).

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

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


EY51, as I recall, in Pye monchrome studio monitors

Yes, three of them!

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

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


NT

Dave Plowman (News) wrote :
All down to costs. Everyone knows digital is perfect so can be used with
no human intervention to check things.

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

In article ,
wrote:
On Monday, 1 January 2018 17:15:22 UTC, Terry Casey wrote:
In article ,
says...
In article ,
tabbypurr wrote:
On Monday, 1 January 2018 14:27:57 UTC, Terry Casey wrote:
In article ,
says...


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).

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

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


EY51, as I recall, in Pye monchrome studio monitors

Yes, three of them!

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

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

Ata guess - for stability of the picture.

--
from KT24 in Surrey, England

On Monday, 1 January 2018 21:17:39 UTC, charles wrote:
In article ,
tabbypurr wrote:
On Monday, 1 January 2018 17:15:22 UTC, Terry Casey wrote:
In article ,
says...
In article ,
tabbypurr wrote:
On Monday, 1 January 2018 14:27:57 UTC, Terry Casey wrote:
In article ,
says...


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).

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

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


EY51, as I recall, in Pye monchrome studio monitors

Yes, three of them!

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

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

Ata guess - for stability of the picture.

multipliers reduce EHT stability. They also, by introducing RC type time delays, reduce the effectiveness of the usual practice in valve sets of letting B+ voltages waver all over the place, designing the set so everything compensates and the picture doesn't shift.


NT