As it's the only such prog. for decades, I don't want to criticise it
too much. This week's does feature some actual electronics - a valved
wireless, and an '80s boombox (as well as a food mixer that has more
electronics than I expected).

But basic TV presentation? This component has failed, here's the
replacement - out of focus? hardly any close-ups? A whole second to look
at them, if we're lucky? Also, the odd block diagramme wouldn't go amiss
- not enough to frighten the children/horses, but none at all is too
few. The voice commentary actually isn't bad at explaining things (to a
near-zero knowledge audience anyway), but would certainly benefit from
some visual aids. (It has good AD.)

One wonders who the prog. is actually aimed at. I'm sure a lot of it is
entertainment only - here are some funny men (they have all been men so
far, I think) who fix things as a sort of strange hobby; however, it
_does_ give some information on how things work. But not at people like
us.
--
J. P. Gilliver. UMRA: 1960/<1985 MB++G()AL-IS-Ch++(p)Ar@T+H+Sh0!:`)DNAf

It's quickly getting to a place where privacy will be cause for suspicion.
- Mayayana in alt.windows7.general, 2018-11-6.

J. P. Gilliver wrote:

> As it's the only such prog. for decades, I don't want to criticise it
> too much. This week's does feature some actual electronics - a valved
> wireless, and an '80s boombox (as well as a food mixer that has more
> electronics than I expected).
>
> But basic TV presentation? This component has failed, here's the
> replacement - out of focus? hardly any close-ups? A whole second to
> look at them, if we're lucky? Also, the odd block diagramme wouldn't
> go amiss - not enough to frighten the children/horses, but none at
> all is too few. The voice commentary actually isn't bad at explaining
> things (to a near-zero knowledge audience anyway), but would
> certainly benefit from some visual aids. (It has good AD.)
>
> One wonders who the prog. is actually aimed at. I'm sure a lot of it
> is entertainment only - here are some funny men (they have all been
> men so far, I think) who fix things as a sort of strange hobby;
> however, it does give some information on how things work. But not at
> people like us.

I'm amazed at the prices. ?500 for an old boom box!!

--

On Tue, 15 Aug 2023 22:06:05 +0100, "J. P. Gilliver"
<G6JPG@255soft.uk> wrote:

>As it's the only such prog. for decades, I don't want to criticise it
>too much. This week's does feature some actual electronics - a valved
>wireless, and an '80s boombox (as well as a food mixer that has more
>electronics than I expected).
>
>But basic TV presentation? This component has failed, here's the
>replacement - out of focus? hardly any close-ups? A whole second to look
>at them, if we're lucky? Also, the odd block diagramme wouldn't go amiss
>- not enough to frighten the children/horses, but none at all is too
>few. The voice commentary actually isn't bad at explaining things (to a
>near-zero knowledge audience anyway), but would certainly benefit from
>some visual aids. (It has good AD.)
>
>One wonders who the prog. is actually aimed at. I'm sure a lot of it is
>entertainment only - here are some funny men (they have all been men so
>far, I think) who fix things as a sort of strange hobby; however, it
>_does_ give some information on how things work. But not at people like
>us.

Once you've got into the habit of watching things like Mr Carlson's
Lab, Adamant IT, Northridge Fix and others like them, anything
supposedly informative about electronics on mainstream TV will be a
waste of your time. Youtube channels where the presenter shows us
their own material themselves are incomparably better because they
know what to show us because they understand it and have experience of
it and know what's important to point out. They may also have learnt
from mistakes and sometimes tell us about those so that we can learn
too. Their main objective is that we get to understand something of
the subject matter, whereas the main objective of TV producers is to
concentrate on 'production values' rather than content and make
something attention grabbing and entertaining for other people like
themselves who don't understand it at all.

Rod.

On 16/08/2023 08:52, Roderick Stewart wrote:
>
> Once you've got into the habit of watching things like Mr Carlson's
> Lab, Adamant IT, Northridge Fix and others like them, anything
> supposedly informative about electronics on mainstream TV will be a
> waste of your time. Youtube channels where the presenter shows us
> their own material themselves are incomparably better because they
> know what to show us because they understand it and have experience of
> it and know what's important to point out. They may also have learnt
> from mistakes and sometimes tell us about those so that we can learn
> too. Their main objective is that we get to understand something of
> the subject matter, whereas the main objective of TV producers is to
> concentrate on 'production values' rather than content and make
> something attention grabbing and entertaining for other people like
> themselves who don't understand it at all.
>
You beat me to saying exactly the same

In message <cavodi12o47llmeur2u1tpmmsgovfcobuk@4ax.com> at Wed, 16 Aug
2023 08:52:10, Roderick Stewart <rjfs@escapetime.myzen.co.uk> writes
>On Tue, 15 Aug 2023 22:06:05 +0100, "J. P. Gilliver"
><G6JPG@255soft.uk> wrote:
[]
>>But basic TV presentation? This component has failed, here's the
>>replacement - out of focus? hardly any close-ups? A whole second to look
>>at them, if we're lucky? Also, the odd block diagramme wouldn't go amiss
>>- not enough to frighten the children/horses, but none at all is too
>>few. The voice commentary actually isn't bad at explaining things (to a
>>near-zero knowledge audience anyway), but would certainly benefit from
>>some visual aids. (It has good AD.)
>>
>>One wonders who the prog. is actually aimed at. I'm sure a lot of it is
>>entertainment only - here are some funny men (they have all been men so
>>far, I think) who fix things as a sort of strange hobby; however, it
>>_does_ give some information on how things work. But not at people like
>>us.
>
>Once you've got into the habit of watching things like Mr Carlson's
>Lab, Adamant IT, Northridge Fix and others like them, anything
>supposedly informative about electronics on mainstream TV will be a
>waste of your time. Youtube channels where the presenter shows us

Depends why you think I'm watching them. Sure, I don't expect to learn
anything from them (well, I do learn the odd thing): I'm watching them
mainly to see what they're saying to the general public. And given the
broad level of knowledge - basically from zero (or even negative!) to
marginal - they can't be _that_ informative/educational.

I was just a bit surprised at the poor _technical_ production values in
this one, compared to say "The Repair Shop": no closeups (or out of
focus), very brief looks.

>their own material themselves are incomparably better because they
>know what to show us because they understand it and have experience of
>it and know what's important to point out. They may also have learnt
>from mistakes and sometimes tell us about those so that we can learn
>too. Their main objective is that we get to understand something of

Yes, there is some excellent stuff on YT - either specific (how to
change the screen on a specific make of laptop), or technically
informative (a look at laserdisc players, that sort of thing). But aimed
at people like us - wouldn't be accepted by mainstream commissioning
editors, I fear - though IMO some of them would definitely make good
prog.s. If the fear is that the audience with sufficient knowledge is
niche, then surely the same could be said of opera, many of the BBC4
music genres, football, property porn, and many other prog. types that
they _do_ show.

>the subject matter, whereas the main objective of TV producers is to
>concentrate on 'production values' rather than content and make
>something attention grabbing and entertaining for other people like
>themselves who don't understand it at all.

In which case this particular prog. failed even by those criteria.
>
>Rod.
--
J. P. Gilliver. UMRA: 1960/<1985 MB++G()AL-IS-Ch++(p)Ar@T+H+Sh0!:`)DNAf

I don't see the requirement to upset people. ... There's enough to make fun of
without offending. - Ronnie Corbett, in Radio Times 6-12 August 2011.

No that was right. Last week with the Spectrum, they did not mention quite
why ram chips fail. It was because Uncle Clive bought duff chips with only
half the chip working and then put links in the pcbs to use the good half.
This tended to mean that the quality of the working bit could be said to be
suspect. Certainly most of the ones I had had some stock faults. Ram was the
main one, Then I think it was TRY, which was a little psu to make the p-5v
from the +5 coming out of the regulator, If this failed badly it could take
a ram chip with it, and failed to power add ons like vtx 500 modems and the
like. The ULA often was damaged if things were pulled off the port while it
was powered up, along with tr4.

Those are impossible to source, since the Sinclair ones were made by
Ferranti and thus no longer exist. There used to be a bodge of the most
common failing of a gate using a transistor soldered over the top of the
chip. You can of course still get z80 chips, and if you can still program
Eproms the files to blow these are still out there.
The rubber key membranes are still sold, but are better made these days and
do not crack. The best Spectrum to get was the later series 5 which had the
heat sink in one corner. The ones from issue 2 and up to that were using a
heat sink above the peripherals slot which cooked the membrane and got very
hot when things were plugged in.
Most people tended to put the pcb inside a keyboard case, but I don't think
you can get them any more. There was a better feeling keyboard sold as the
plus upgrade kit, but in my experience, the weak link was still the el
cheapo membranes they used. When Amstrad took it over the keyboard issues
went away, as did overheating.

On the tech level of the show, yes I agree. They never said what he did to
clean up the vintage radios volume control, as from experience there was no
other course but to replace it, since the leaky capacitors around there
would have put DC on it and that is a good way to wear it out.

He was right about aligning it though, these do drift and the new
capacitors would mean you had to do that. Also a good clean up of the
contacts on the tuning capacitor would have been needed, but those were
exceptionally well built in that vintage with air spaced vanes, none of your
mica ones you found in transistor sets that went wrinkly and hence drifted.

I was surprised the double sided record deck was fine after a new stylus a
clen up and new belts. Its been my experience with another one of those that
the thing tends to have major issues with tracking a whole album due to crap
engineering in the various components in pararell tracking arms or worn
bearing in the pivoted arms. Brian

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"J. P. Gilliver" <G6JPG@255soft.uk> wrote in message
news:YRUnRgT9i+2kFw45@255soft.uk...
> As it's the only such prog. for decades, I don't want to criticise it too
> much. This week's does feature some actual electronics - a valved
> wireless, and an '80s boombox (as well as a food mixer that has more
> electronics than I expected).
>
> But basic TV presentation? This component has failed, here's the
> replacement - out of focus? hardly any close-ups? A whole second to look
> at them, if we're lucky? Also, the odd block diagramme wouldn't go amiss -
> not enough to frighten the children/horses, but none at all is too few.
> The voice commentary actually isn't bad at explaining things (to a
> near-zero knowledge audience anyway), but would certainly benefit from
> some visual aids. (It has good AD.)
>
> One wonders who the prog. is actually aimed at. I'm sure a lot of it is
> entertainment only - here are some funny men (they have all been men so
> far, I think) who fix things as a sort of strange hobby; however, it
> _does_ give some information on how things work. But not at people like
> us.
> --
> J. P. Gilliver. UMRA: 1960/<1985 MB++G()AL-IS-Ch++(p)Ar@T+H+Sh0!:`)DNAf
>
> It's quickly getting to a place where privacy will be cause for suspicion.
> - Mayayana in alt.windows7.general, 2018-11-6.

Yes I think I'd only go to 200 for the boombox, even if it is a rare one,
most of the ones I've seen are double cassette and some of the later ones
were quite sophisticated having Dolby and electronic counter. Really those
belt driven ones were a waste of space. I had an akai which relied on that
belt to operate the autostop switch, so when it stalled the recording
stopped. I ended up with a hall effect device and a tiny changeover relay
and a magnet araldite to the take up spool directly.
Brian

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"Ashley Booth" <removetab@snglinks.com> wrote in message
news:kk3bv5FrigjU1@mid.individual.net...
> J. P. Gilliver wrote:
>
>> As it's the only such prog. for decades, I don't want to criticise it
>> too much. This week's does feature some actual electronics - a valved
>> wireless, and an '80s boombox (as well as a food mixer that has more
>> electronics than I expected).
>>
>> But basic TV presentation? This component has failed, here's the
>> replacement - out of focus? hardly any close-ups? A whole second to
>> look at them, if we're lucky? Also, the odd block diagramme wouldn't
>> go amiss - not enough to frighten the children/horses, but none at
>> all is too few. The voice commentary actually isn't bad at explaining
>> things (to a near-zero knowledge audience anyway), but would
>> certainly benefit from some visual aids. (It has good AD.)
>>
>> One wonders who the prog. is actually aimed at. I'm sure a lot of it
>> is entertainment only - here are some funny men (they have all been
>> men so far, I think) who fix things as a sort of strange hobby;
>> however, it does give some information on how things work. But not at
>> people like us.
>
> I'm amazed at the prices. ?500 for an old boom box!!
>
> --
>

Yes so why don't they save their budget and pay for the youtube stuff and
shove it on mainstream telly?
I think its deliberate, IE its like a for idiots guide almost. What is
missing is a ref to some of those Youtube channels if this has pricked your
interest.
Even I can remember the number of people back in the day who managed to
blow the tweeters in their speakers due to clipping in the amplifier. I and
a friend found that many of these speakers supplied with hi fis with these
underpowered amps, no matter what tweeter they used there was a peerless
one that worked and you could tweak the crossover values a bit if it was too
bright or too dull. We also fitted fast blow fuses while we were at it.
Brian

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"Roderick Stewart" <rjfs@escapetime.myzen.co.uk> wrote in message
news:cavodi12o47llmeur2u1tpmmsgovfcobuk@4ax.com...
> On Tue, 15 Aug 2023 22:06:05 +0100, "J. P. Gilliver"
> <G6JPG@255soft.uk> wrote:
>
>>As it's the only such prog. for decades, I don't want to criticise it
>>too much. This week's does feature some actual electronics - a valved
>>wireless, and an '80s boombox (as well as a food mixer that has more
>>electronics than I expected).
>>
>>But basic TV presentation? This component has failed, here's the
>>replacement - out of focus? hardly any close-ups? A whole second to look
>>at them, if we're lucky? Also, the odd block diagramme wouldn't go amiss
>>- not enough to frighten the children/horses, but none at all is too
>>few. The voice commentary actually isn't bad at explaining things (to a
>>near-zero knowledge audience anyway), but would certainly benefit from
>>some visual aids. (It has good AD.)
>>
>>One wonders who the prog. is actually aimed at. I'm sure a lot of it is
>>entertainment only - here are some funny men (they have all been men so
>>far, I think) who fix things as a sort of strange hobby; however, it
>>_does_ give some information on how things work. But not at people like
>>us.
>
> Once you've got into the habit of watching things like Mr Carlson's
> Lab, Adamant IT, Northridge Fix and others like them, anything
> supposedly informative about electronics on mainstream TV will be a
> waste of your time. Youtube channels where the presenter shows us
> their own material themselves are incomparably better because they
> know what to show us because they understand it and have experience of
> it and know what's important to point out. They may also have learnt
> from mistakes and sometimes tell us about those so that we can learn
> too. Their main objective is that we get to understand something of
> the subject matter, whereas the main objective of TV producers is to
> concentrate on 'production values' rather than content and make
> something attention grabbing and entertaining for other people like
> themselves who don't understand it at all.
>
> Rod.

I learned a valuable lesson about glass dials in Valve radios. Do not use
any kind of liquid to clean then, not even water, as they are often not
bonded very well and tend to just melt away or move. Just use a soft brush
and a vacuum. The best ones of course are engraved, so the dial lights
refract on the cuts and illuminate them. I have one Lafayette radio with
just glass in it now, sulk.
Brian

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"Mark Carver" <mark.carver@invalid.invalid> wrote in message
news:kk3e5dFrkbbU1@mid.individual.net...
> On 16/08/2023 08:52, Roderick Stewart wrote:
>>
>> Once you've got into the habit of watching things like Mr Carlson's
>> Lab, Adamant IT, Northridge Fix and others like them, anything
>> supposedly informative about electronics on mainstream TV will be a
>> waste of your time. Youtube channels where the presenter shows us
>> their own material themselves are incomparably better because they
>> know what to show us because they understand it and have experience of
>> it and know what's important to point out. They may also have learnt
>> from mistakes and sometimes tell us about those so that we can learn
>> too. Their main objective is that we get to understand something of
>> the subject matter, whereas the main objective of TV producers is to
>> concentrate on 'production values' rather than content and make
>> something attention grabbing and entertaining for other people like
>> themselves who don't understand it at all.
>>
> You beat me to saying exactly the same
>

On 16/08/2023 08:52, Roderick Stewart wrote:
> Once you've got into the habit of watching things like Mr Carlson's
> Lab, Adamant IT, Northridge Fix and others like them, anything
> supposedly informative about electronics on mainstream TV will be a
> waste of your time. Youtube channels where the presenter shows us
> their own material themselves are incomparably better because they
> know what to show us because they understand it and have experience of
> it and know what's important to point out.

This guy does a deep dive into schematics at times, both TVs and computers,

"I replaced the main board of this TV with brand new parts made in 2023!"
https://www.youtube.com/watch?v=MoqflFfvkR0

Though I'd be a bit concerned about X-rays ...

--
Adrian C

On Wed, 16 Aug 2023 11:43:47 +0100, "Brian Gaff"
<brian1gaff@gmail.com> wrote:

>Yes so why don't they save their budget and pay for the youtube stuff and
>shove it on mainstream telly?

It's been done, but I don't think the mainstream channels would want
to do it very often as they'd find it hard to justify the money they'd
want from advertisers or licence payers to broadcast material that
Youtube presenters typically make themselves on a shoestring budget.

They might also struggle to justify all the people they need to do it,
when a lot of Youtube material seems to require only one person,
occasionally with one or two assistants.

A startling example of this is the series of programmes the BBC made
with Youtube presenter Ogmios, who had been making his own series of
programmes called the 'Ogmios School of Zen Motoring' just by driving
around London with a dashcam and commenting on what he sees. From my
description it might sound very dull, but he makes it interesting.
Watch the originals on Youtube, not the BBC programmes. I could only
bear to watch one of the BBC programmes as they had little of the
character of the originals, including bits of completely gratuitous
CGI gimmickry, and most horrifying of all, a stream of dozens of names
in the end credits that whizzed up the screen faster than I could even
count them, never mind read them. Presumably all those people had to
be paid for whatever they did, but what exactly could they be
contributing to a show that one person was perfectly capable of
creating all by himself?

Rod.

On Wed, 16 Aug 2023 13:40:32 +0100, Adrian Caspersz
<email@here.invalid> wrote:

>This guy does a deep dive into schematics at times, both TVs and computers,
>
>"I replaced the main board of this TV with brand new parts made in 2023!"
>https://www.youtube.com/watch?v=MoqflFfvkR0
>
>
>Though I'd be a bit concerned about X-rays ...

I thought most of the concern about x-rays in early colour TVs was
because they generated the EHT as a 25kV pulse which was then
rectified by a single thermionic valve. I may be wrong but my
understanding is that x-rays are generated when a high voltage stream
of electrons hits something in a vacuum. More recent TVs only
generated a pulse of about 8kV and didn't use valves at all, and no
semiconductor had the full 25kV across it, so does this still apply?

Rod.

On 16/08/2023 13:40, Adrian Caspersz wrote:
> On 16/08/2023 08:52, Roderick Stewart wrote:
>> Once you've got into the habit of watching things like Mr Carlson's
>> Lab, Adamant IT, Northridge Fix and others like them, anything
>> supposedly informative about electronics on mainstream TV will be a
>> waste of your time. Youtube channels where the presenter shows us
>> their own material themselves are incomparably better because they
>> know what to show us because they understand it and have experience of
>> it and know what's important to point out.
>
> This guy does a deep dive into schematics at times, both TVs and computers,
>
> "I replaced the main board of this TV with brand new parts made in 2023!"
> https://www.youtube.com/watch?v=MoqflFfvkR0
>
>
> Though I'd be a bit concerned about X-rays ...
>
For many decades now, domestic TV sets have used CRT's with a lead glass
faceplate. Alternatives are Bsarium-Strontium alloys.

Both are very good at stopping the X Rays generated when the electron
beam hits the phosphor.

--
Tciao for Now!

John.

On Wed, 16 Aug 2023 14:37:47 +0100, Roderick Stewart
<rjfs@escapetime.myzen.co.uk> wrote:

>On Wed, 16 Aug 2023 13:40:32 +0100, Adrian Caspersz
><email@here.invalid> wrote:
>
>>This guy does a deep dive into schematics at times, both TVs and computers,
>>
>>"I replaced the main board of this TV with brand new parts made in 2023!"
>>https://www.youtube.com/watch?v=MoqflFfvkR0
>>
>>
>>Though I'd be a bit concerned about X-rays ...
>
>I thought most of the concern about x-rays in early colour TVs was
>because they generated the EHT as a 25kV pulse which was then
>rectified by a single thermionic valve. I may be wrong but my
>understanding is that x-rays are generated when a high voltage stream
>of electrons hits something in a vacuum. More recent TVs only
>generated a pulse of about 8kV and didn't use valves at all, and no
>semiconductor had the full 25kV across it, so does this still apply?
>
>Rod.

Coincidence! I just sent some comments about colour TV. I was one of
the first engineers trained on colour TV, both NTSC and then PAL so I
was supposed to be an expert. I remember "rumours" about standing too
close to the early THORN sets. I would think that screening on the CRT
would stop any x-rays.

In message <4qjpdid34dklte2ube5meadnuga2jeh3k3@4ax.com> at Wed, 16 Aug
2023 14:37:47, Roderick Stewart <rjfs@escapetime.myzen.co.uk> writes
>On Wed, 16 Aug 2023 13:40:32 +0100, Adrian Caspersz
><email@here.invalid> wrote:
>
>>This guy does a deep dive into schematics at times, both TVs and computers,
>>
>>"I replaced the main board of this TV with brand new parts made in 2023!"
>>https://www.youtube.com/watch?v=MoqflFfvkR0
>>
>>
>>Though I'd be a bit concerned about X-rays ...
>
>I thought most of the concern about x-rays in early colour TVs was

Electrons travelling at speed hitting something is what generates X rays
(even some X ray machines used that principle, though I think less so
nowadays).

>because they generated the EHT as a 25kV pulse which was then

The EHT was generated by the line output transformer - generally, the
bigger the CRT the higher the voltage (I think the little Sinclair TVs
used 1 kV, "bigger" CRTs - which mostly meant twentysomething inch! - up
to, indeed, 25 kV). Colour needed a _bit_ more, but it was really more
current rather than voltage, as only (slightly less than, towards the
end - a lot less initially) a third of the fired electrons actually
reached the screen. The LOPT produced the pulses at, indeed, line
frequency.

>rectified by a single thermionic valve. I may be wrong but my

Solid-state stick rectifiers for EHT did exist; since I managed to
replace the thermionic one in a small (11" I think) set with a stick
one, many decades ago, I presume the solid-state ones were the norm by
the end. The thermionic valve was interesting - it was DY something, the
D meaning I think 2 volt heater rather than the usual E 6.3V - because,
due to the need for isolation, its heater was powered by a few turns off
the LOPT, rather than the normal heater supply. (Well, there wasn't I
think much of a heater supply - that set was all solid state - though
the CRT itself must have had one.)

>understanding is that x-rays are generated when a high voltage stream
>of electrons hits something in a vacuum. More recent TVs only
>generated a pulse of about 8kV and didn't use valves at all, and no
>semiconductor had the full 25kV across it, so does this still apply?
>
>Rod.

No, very roughly, a kV per inch of screen size, so bigger sets still
needed twentysomething kV. Which still had to be rectified, though as I
say I think the rectification was solid state (the one I got for that
little set was shaped like a short pencil - a little rod). Indeed, not
_that_ long after colour became common, sets didn't have any valves in
them, other than the CRT itself which is a valve. (_Early_ colour sets
had lots of valves, and did quite a good job of heating the room!)

Of course, more recent sets don't use CRTs, so no EHT needed. Most early
flat-screen sets used a fluorescent backlight, so three figures of volts
- I don't know if any such are still being made, or if they've all gone
to LEDs now. Oh, plasma sets involved quite high voltages too, but I
don't think they're still made either - even for big sets for stadium
and similar use. Though I'm sure there are plenty still in use. (They're
not very energy-efficient, so - as well as the difficulty of finding
anywhere to repair them anyway - I suspect most are replaced rather than
repaired when they go wrong.)
--
J. P. Gilliver. UMRA: 1960/<1985 MB++G()AL-IS-Ch++(p)Ar@T+H+Sh0!:`)DNAf

The first objective of any tyrant in Whitehall would be to make Parliament
utterly subservient to his will; and the next to overturn or diminish trial by
jury ..." Lord Devlin (http://www.holbornchambers.co.uk)

On Wed, 16 Aug 2023 15:16:12 +0100, Stephen Wolstenholme
<stephenwolstenholme30@outlook.com> wrote:

>On Wed, 16 Aug 2023 14:37:47 +0100, Roderick Stewart
><rjfs@escapetime.myzen.co.uk> wrote:
>
>>On Wed, 16 Aug 2023 13:40:32 +0100, Adrian Caspersz
>><email@here.invalid> wrote:
>>
>>>This guy does a deep dive into schematics at times, both TVs and computers,
>>>
>>>"I replaced the main board of this TV with brand new parts made in 2023!"
>>>https://www.youtube.com/watch?v=MoqflFfvkR0
>>>
>>>
>>>Though I'd be a bit concerned about X-rays ...
>>
>>I thought most of the concern about x-rays in early colour TVs was
>>because they generated the EHT as a 25kV pulse which was then
>>rectified by a single thermionic valve. I may be wrong but my
>>understanding is that x-rays are generated when a high voltage stream
>>of electrons hits something in a vacuum. More recent TVs only
>>generated a pulse of about 8kV and didn't use valves at all, and no
>>semiconductor had the full 25kV across it, so does this still apply?
>>
>>Rod.
>
>Coincidence! I just sent some comments about colour TV. I was one of
>the first engineers trained on colour TV, both NTSC and then PAL so I
>was supposed to be an expert. I remember "rumours" about standing too
>close to the early THORN sets. I would think that screening on the CRT
>would stop any x-rays.

In the BBC workshops there were little glass tubes that we could fit
over the EHT rectifier valve if we had to spend any time round the
back of a display monitor. They were made of special glass intended to
reduce x-rays, and it was specifically the EHT rectifier that was said
to present the most danger. I suppose the x-rays would be generated by
the electrons hitting the anode of the rectifier. Those early monitors
used a 25kV pulse, unlike later ones that used smaller pulses and a
kind of zigzag arrangement of diodes and capacitors as a voltage
multiplier, usually a tripler. CRT displays are designed for people to
sit in front of them, so I don't think there can have been much x-ray
emission from the front.

Rod.

In message <p3hrdi1k7rjf0770m2eugmp3lgd1o9jq4a@4ax.com> at Thu, 17 Aug
2023 08:12:29, Roderick Stewart <rjfs@escapetime.myzen.co.uk> writes
[]
>In the BBC workshops there were little glass tubes that we could fit
>over the EHT rectifier valve if we had to spend any time round the
>back of a display monitor. They were made of special glass intended to
>reduce x-rays, and it was specifically the EHT rectifier that was said
>to present the most danger. I suppose the x-rays would be generated by
>the electrons hitting the anode of the rectifier. Those early monitors

Sounds plausible; the rectifier valve normally being inside the set and
so behind the CRT faceplate, and usually inside a metal structure
anyway, the manufacturers of said valves probably didn't want to
incorporate such into the valves themselves.

>used a 25kV pulse, unlike later ones that used smaller pulses and a
>kind of zigzag arrangement of diodes and capacitors as a voltage
>multiplier, usually a tripler. CRT displays are designed for people to

I don't think I've ever heard of the zigzag type of multiplier ever
being used with thermionic rectifiers (you'd need several such,
obviously), so I think they only became practical with solid-state
rectifiers.

>sit in front of them, so I don't think there can have been much x-ray
>emission from the front.
>
>Rod.

That's why (or one of the reasons) they were so heavy: they included a
good thickness of glass, I think lead glass, to protect viewers.

I remember TV cabinets from 405-line days often had a plate of quite
thick glass in the front (as part of the cabinet); I was never sure if
that was to protect viewers in case of tube implosion, or from X-rays;
probably a bit of both. Or to protect the CRT from damage from the
viewer (or their dog, child, whatever)!
--
J. P. Gilliver. UMRA: 1960/<1985 MB++G()AL-IS-Ch++(p)Ar@T+H+Sh0!:`)DNAf

Science fiction is escape into reality - Arthur C Clarke

On Thu, 17 Aug 2023 09:27:13 +0100, "J. P. Gilliver"
<G6JPG@255soft.uk> wrote:

>I don't think I've ever heard of the zigzag type of multiplier ever
>being used with thermionic rectifiers (you'd need several such,
>obviously), so I think they only became practical with solid-state
>rectifiers.

They were rare, though I did once encounter a tripler with wire ended
valve rectifiers (EY51?) inside a sealed oil filled metal can. The
price of curiosity was a right old mess that day. Triplers were more
common in later designs with semiconductor diodes and capacitors
potted in something solid.

The advantage of using a tripler would be that no individual component
would have the full voltage across it (except the CRT itself of
course). The same would apply to the transformer, which was only
required to produce an 8kV pulse rather than the full 25kV. The
secondary transformer windings in the older designs even had to be
wound in a thin disk shape so that both ends of the wire would be
sufficiently far apart to withstand the high voltage. Triplers made
the mechanical arrangement of everything slightly easier.

Rod.

On Thu, 17 Aug 2023 08:12:29 +0100, Roderick Stewart
<rjfs@escapetime.myzen.co.uk> wrote:

>On Wed, 16 Aug 2023 15:16:12 +0100, Stephen Wolstenholme
><stephenwolstenholme30@outlook.com> wrote:
>
>>On Wed, 16 Aug 2023 14:37:47 +0100, Roderick Stewart
>><rjfs@escapetime.myzen.co.uk> wrote:
>>
>>>On Wed, 16 Aug 2023 13:40:32 +0100, Adrian Caspersz
>>><email@here.invalid> wrote:
>>>
>>>>This guy does a deep dive into schematics at times, both TVs and computers,
>>>>
>>>>"I replaced the main board of this TV with brand new parts made in 2023!"
>>>>https://www.youtube.com/watch?v=MoqflFfvkR0
>>>>
>>>>
>>>>Though I'd be a bit concerned about X-rays ...
>>>
>>>I thought most of the concern about x-rays in early colour TVs was
>>>because they generated the EHT as a 25kV pulse which was then
>>>rectified by a single thermionic valve. I may be wrong but my
>>>understanding is that x-rays are generated when a high voltage stream
>>>of electrons hits something in a vacuum. More recent TVs only
>>>generated a pulse of about 8kV and didn't use valves at all, and no
>>>semiconductor had the full 25kV across it, so does this still apply?
>>>
>>>Rod.
>>
>>Coincidence! I just sent some comments about colour TV. I was one of
>>the first engineers trained on colour TV, both NTSC and then PAL so I
>>was supposed to be an expert. I remember "rumours" about standing too
>>close to the early THORN sets. I would think that screening on the CRT
>>would stop any x-rays.
>
>In the BBC workshops there were little glass tubes that we could fit
>over the EHT rectifier valve if we had to spend any time round the
>back of a display monitor. They were made of special glass intended to
>reduce x-rays, and it was specifically the EHT rectifier that was said
>to present the most danger. I suppose the x-rays would be generated by
>the electrons hitting the anode of the rectifier. Those early monitors
>used a 25kV pulse, unlike later ones that used smaller pulses and a
>kind of zigzag arrangement of diodes and capacitors as a voltage
>multiplier, usually a tripler. CRT displays are designed for people to
>sit in front of them, so I don't think there can have been much x-ray
>emission from the front.
>
>Rod.

I once had to "maintain" an Italian gadget that projected film or TV
images onto a layer of oil and the reflection was displayed on a
cinema screen. I don't think that it could have produced x-rays but it
was impossible to get to the actual projector as it was locked in a
very secure metal cylinder. The maintenance was mainly cleaning fans
and filters. Before maintenance we had to allow 2 hours for it to cool
down. I've a vague memory that it was made by a company called Cintela
but that's now a sunscreen cream.

> I once had to "maintain" an Italian gadget that projected film or
> TV images onto a layer of oil and the reflection was displayed on a
> cinema screen.

Probably the Swiss https://en.wikipedia.org/wiki/Eidophor

Only way to get bright cinema sized TV screens until LED walls, LCD and DLP
projectors came along.

Angus

Angus Robertson wrote:

> steve1001908@outlook.com wrote:
>
>> I once had to "maintain" an Italian gadget that projected film or
>> TV images onto a layer of oil and the reflection was displayed on a
>> cinema screen.
>
> Probably the Swiss https://en.wikipedia.org/wiki/Eidophor
>
> Only way to get bright cinema sized TV screens until LED walls, LCD and DLP
> projectors came along.

Or a G.E Telaria

In message <kk6kkkFaskvU2@mid.individual.net> at Thu, 17 Aug 2023
14:11:50, Andy Burns <usenet@andyburns.uk> writes
>Angus Robertson wrote:
>
>> steve1001908@outlook.com wrote:
>>
>>> I once had to "maintain" an Italian gadget that projected film or
>>> TV images onto a layer of oil and the reflection was displayed on a
>>> cinema screen.
>> Probably the Swiss https://en.wikipedia.org/wiki/Eidophor
>> Only way to get bright cinema sized TV screens until LED walls, LCD
>>and DLP
>> projectors came along.
>
>Or a G.E Telaria
>
>
Weren't there some systems that used lasers, and either a mirror-drum or
coil-controlled mirrors? (Or was the Telaria such?)
--
J. P. Gilliver. UMRA: 1960/<1985 MB++G()AL-IS-Ch++(p)Ar@T+H+Sh0!:`)DNAf

resentment is like drinking poison and expecting the other person to die -
attributed to Carrie Fisher by Gareth McLean, in Radio Times 28 January-3
February 2012

On Thu, 17 Aug 2023 15:44:24 +0100, "J. P. Gilliver"
<G6JPG@255soft.uk> wrote:

>In message <kk6kkkFaskvU2@mid.individual.net> at Thu, 17 Aug 2023
>14:11:50, Andy Burns <usenet@andyburns.uk> writes
>>Angus Robertson wrote:
>>
>>> steve1001908@outlook.com wrote:
>>>
>>>> I once had to "maintain" an Italian gadget that projected film or
>>>> TV images onto a layer of oil and the reflection was displayed on a
>>>> cinema screen.
>>> Probably the Swiss https://en.wikipedia.org/wiki/Eidophor
>>> Only way to get bright cinema sized TV screens until LED walls, LCD
>>>and DLP
>>> projectors came along.
>>
>>Or a G.E Telaria
>>
>>
>Weren't there some systems that used lasers, and either a mirror-drum or
>coil-controlled mirrors? (Or was the Telaria such?)

The Swiss Eidophor system using a layer of oil was around but I don't
know how "similar" it was to the Italian system.

J. P. Gilliver wrote:

> Andy Burns writes:
>
>> Angus Robertson wrote:
>>
>>> Probably the Swiss https://en.wikipedia.org/wiki/Eidophor
>>
>> Or a G.E Telaria
>
> Weren't there some systems that used lasers, and either a mirror-drum or
> coil-controlled mirrors?

Probably came later, these two are 1940/50's and 1970/80's

> (Or was the Telaria such?)

It also used an oil film, Mike Harrison got hold of one and tore it down
as he does with lots of other "electric stuff".

<https://youtu.be/PjKzCRkc7Ew>

He does a talk about the Eidophor too

<https://youtu.be/3-BvMcqEc98?t=72>

> The Swiss Eidophor system using a layer of oil was around but I
> don't know how "similar" it was to the Italian system.

I was a journalist in the late seventies and wrote about the dozen or more TV
projection systems available in the UK, don't recall any Italian system but
maybe that was overseas only.

I remember watching the first Star Wars film on an Advent system in my living
room off NTSC U-Matic with a lot of visitors, the summer before it was released
here.

Most systems used three CRTs and lenses, apart from Eidophor and General
Electric that used a xenon lamp and transmission light valve but only bright
enough for a 6m screen, 10 times lower than the largest Eidophor.

Angus