Retro Electro Workshop (Yesterday)

[J. P. Gilliver]

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.

[Ashley Booth]

Post by J. P. Gilliver
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!!

--

[Brian Gaff]

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
--
--:
This newsgroup posting comes to you directly from...
The Sofa of Brian Gaff...
***@blueyonder.co.uk
Blind user, so no pictures please
Note this Signature is meaningless.!

Post by Ashley Booth

Post by J. P. Gilliver
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!!
--

[Max Demian]

Post by Ashley Booth

Post by J. P. Gilliver
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!!

I was impressed by the prices for the Commodore+Spectrum combo in the
previous episode. They were expecting £100's but got £10. Except they
didn't, as there was £5 for the new switch for the Commodore. So £5 profit.

I've never seen a portable player that plays LPs. I remember the ones
that played 7" singles (vertically) around 1970. And there were ones in
cars. Then Musicassettes came in and everyone used them in their "ghetto
blasters".

I'm not sure who this programme is intended for either. Just a nostalgia
trip I think. I liked the way they summarised the functions of
capacitors in radios as coupling, decoupling, smoothing and tuning.
(Wow! coupling /and/ de-coupling!)

[Liz Tuddenham]

Max Demian <***@bigfoot.com> wrote:

[...]

Post by Max Demian
I liked the way they summarised the functions of
capacitors in radios as coupling, decoupling, smoothing and tuning.
(Wow! coupling /and/ de-coupling!)

That's always been a difficult one to explain to beginners. If it goes
to earth, it can decouple two circuit that share the same power supply
because it couples the voltage variations to earth.

It is a bit like a nut and bolt, it can fix two items together so that
movement of one is transferred to tha other - or it can stop one of them
moving if the other one happens to be firmly fixed.

[J. P. Gilliver]

In message <1qfttdw.1v3yvhizoejzcN%***@poppyrecords.invalid.invalid> at
Mon, 21 Aug 2023 18:49:07, Liz Tuddenham

Post by Liz Tuddenham
[...]

Post by Max Demian
I liked the way they summarised the functions of
capacitors in radios as coupling, decoupling, smoothing and tuning.
(Wow! coupling /and/ de-coupling!)

That's always been a difficult one to explain to beginners. If it goes
to earth, it can decouple two circuit that share the same power supply
because it couples the voltage variations to earth.
It is a bit like a nut and bolt, it can fix two items together so that
movement of one is transferred to tha other - or it can stop one of them
moving if the other one happens to be firmly fixed.

Good analogy.
Another concept is the relativity of signals. I can't remember where I
was confused and what enlightened me: I think it was that US circuits
(or "schematics") tended much more to _not_ draw a line along the bottom
of the signal flow path, instead just liberally sprinking earth or
ground symbols. I think it might have been a car wiring diag. that
caused me to see the light. (When car wiring tended to actually _use_
the chassis more.)

[Liz Tuddenham]

Post by J. P. Gilliver
Mon, 21 Aug 2023 18:49:07, Liz Tuddenham

Post by Liz Tuddenham
[...]

Post by Max Demian
I liked the way they summarised the functions of
capacitors in radios as coupling, decoupling, smoothing and tuning.
(Wow! coupling /and/ de-coupling!)

That's always been a difficult one to explain to beginners. If it goes
to earth, it can decouple two circuit that share the same power supply
because it couples the voltage variations to earth.
It is a bit like a nut and bolt, it can fix two items together so that
movement of one is transferred to tha other - or it can stop one of them
moving if the other one happens to be firmly fixed.

Good analogy.
Another concept is the relativity of signals. I can't remember where I
was confused and what enlightened me: I think it was that US circuits
(or "schematics") tended much more to _not_ draw a line along the bottom
of the signal flow path, instead just liberally sprinking earth or
ground symbols. I think it might have been a car wiring diag. that
caused me to see the light. (When car wiring tended to actually _use_
the chassis more.)

Drawing circuit diagrams so they explain what is going on is as much an
art as a science. Suppose you have a sensitive amplifier where earth
circulating currents could introduce spurious signals between sections
that are both nominally connected to 'earth', so the earth line is
really part of the signal path.

I tend to represent this either with diagonal earth connections to one
single point or with a separate section of earth line for that section
of the amplifier, offset vertically and joined to the rest with a
thinner vertical line. I have also seen it done by lettering or
numbering the 'floating' earth points, but the intention is not
immediately obvious at a glance and it takes time and effort to compare
numbers.

Where 'floating' earth points can be a great help is along the + line at
the top of the diagram. That saves a lot of vertical lines from
decoupling capacitors down to the earth line, threading their way
between signal lines and components. Alternatively they can be shown
connected to a short section of earth line near the top, with one
vertical down to the main earth line.

[J. P. Gilliver]

In message <uc05pm$200ln$***@dont-email.me> at Mon, 21 Aug 2023 18:10:15,
Max Demian <***@bigfoot.com> writes
[]

Post by Max Demian
I'm not sure who this programme is intended for either. Just a
nostalgia trip I think. I liked the way they summarised the functions

Except I'd say it gives _slightly_ too much technical detail for just
that.

Post by Max Demian
of capacitors in radios as coupling, decoupling, smoothing and tuning.
(Wow! coupling /and/ de-coupling!)

[Roderick Stewart]

On Tue, 15 Aug 2023 22:06:05 +0100, "J. P. Gilliver"

Post by J. P. Gilliver
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.

[Mark Carver]

Post by Roderick Stewart
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

[Brian Gaff]

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
--
--:
This newsgroup posting comes to you directly from...
The Sofa of Brian Gaff...
***@blueyonder.co.uk
Blind user, so no pictures please
Note this Signature is meaningless.!

Post by Mark Carver

Post by Roderick Stewart
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

[J. P. Gilliver]

Post by Roderick Stewart
On Tue, 15 Aug 2023 22:06:05 +0100, "J. P. Gilliver"

[]

Post by Roderick Stewart

Post by J. P. Gilliver
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.

Post by Roderick Stewart
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.

Post by Roderick Stewart
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.

Post by Roderick Stewart
Rod.

[Brian Gaff]

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
--
--:
This newsgroup posting comes to you directly from...
The Sofa of Brian Gaff...
***@blueyonder.co.uk
Blind user, so no pictures please
Note this Signature is meaningless.!

Post by Roderick Stewart
On Tue, 15 Aug 2023 22:06:05 +0100, "J. P. Gilliver"

Post by J. P. Gilliver
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.

[Roderick Stewart]

On Wed, 16 Aug 2023 11:43:47 +0100, "Brian Gaff"

Post by Brian Gaff
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.

[Adrian Caspersz]

Post by Roderick Stewart
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!"

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

[Roderick Stewart]

On Wed, 16 Aug 2023 13:40:32 +0100, Adrian Caspersz

Post by Adrian Caspersz
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!"
http://youtu.be/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.

[Stephen Wolstenholme]

On Wed, 16 Aug 2023 14:37:47 +0100, Roderick Stewart

Post by Roderick Stewart
On Wed, 16 Aug 2023 13:40:32 +0100, Adrian Caspersz

Post by Adrian Caspersz
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!"
http://youtu.be/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.

[Roderick Stewart]

On Wed, 16 Aug 2023 15:16:12 +0100, Stephen Wolstenholme

Post by Stephen Wolstenholme
On Wed, 16 Aug 2023 14:37:47 +0100, Roderick Stewart

Post by Roderick Stewart
On Wed, 16 Aug 2023 13:40:32 +0100, Adrian Caspersz

Post by Adrian Caspersz
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!"
http://youtu.be/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.

[J. P. Gilliver]

In message <***@4ax.com> at Thu, 17 Aug
2023 08:12:29, Roderick Stewart <***@escapetime.myzen.co.uk> writes
[]

Post by Roderick Stewart
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.

Post by Roderick Stewart
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.

Post by Roderick Stewart
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)!

[Roderick Stewart]

On Thu, 17 Aug 2023 09:27:13 +0100, "J. P. Gilliver"

Post by J. P. Gilliver
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.

[Liz Tuddenham]

J. P. Gilliver <***@255soft.uk> wrote:

[...]

Post by J. P. Gilliver
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.

Look up high voltage accelerators in Philips Technical Review. They
used thermionic rectifiers in Cockroft-Walton multipliers with the valve
heaters supplied by H.F. energy circulating through the capacitors.
Very clever.

[Liz Tuddenham]

J. P. Gilliver <***@255soft.uk> wrote:

[...]

Post by J. P. Gilliver
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.

https://worldradiohistory.com/Archive-Company-Publications/Philips-Techn
ical-Review/40s/Philips-Technical-Review-1949.pdf

Page 123:
"Heating the Filaments of Valves in a Cascade Generator by Means of High
Frequency Current" by Tj. Douma & H.P.J. Brekoo.

[J. P. Gilliver]

In message <1qgojd0.8wdt9v1qiaif4N%***@poppyrecords.invalid.invalid> at
Thu, 7 Sep 2023 08:56:22, Liz Tuddenham

Post by Liz Tuddenham
[...]

Post by J. P. Gilliver
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.

https://worldradiohistory.com/Archive-Company-Publications/Philips-Techn
ical-Review/40s/Philips-Technical-Review-1949.pdf
"Heating the Filaments of Valves in a Cascade Generator by Means of High
Frequency Current" by Tj. Douma & H.P.J. Brekoo.

Most ingenious! I think only for professional equipment, though. Clever
to pass the h. f. up the same lines as the (presumably mains) frequency
being used to generate the EHT.

Of course, in a TV set the signal being rectified is moderately h. f.
(compared to mains, anyway). The only case I've come across in a TV set
was a little (11"?) dual-standard portable, which had a little D (2V)
valve hidden inside the LOPT casing (DY91 rings a bell?); it had two
(IIRR) turns of thicker wire wound round the LOPT core to drive its
heater. (Very simple valve - about the shape and size of a gherkin; just
a single pin sticking out the top for the EHT, I can't remember what it
had at the base.) I replaced it with a solid-state stick - can't
remember why, I think it became intermittent. (The stick gave a brighter
slightly smaller picture - I presume higher voltage, so brighter and
deflected less.) I never worked on (the EHT part of, anyway) any bigger
set, so I don't know if any used multiple valve rectifiers in a
multiplier arrangement; I'd have thought that would be a complex and
error-prone thing to design and keep going in a domestic setting
(compared to doing it with solid-state stick rectifiers when those
became available), but I could be wrong.

[Liz Tuddenham]

... The only case I've come across in a TV set
was a little (11"?) dual-standard portable, which had a little D (2V)
valve hidden inside the LOPT casing (DY91 rings a bell?); it had two
(IIRR) turns of thicker wire wound round the LOPT core to drive its
heater.

They were usually EY51 (6.3v heater). They had no base, so the
heater/cathode wires were soldered to the terminals of the LOPT with big
rounded solder blobs to reduce corona discharge. Possibly a DY51, with
lower heater requirements, would have been used in a portable set.


EY51s were also used in the tripler of the Philips projection
television, immersed in oil and sealed in a metal can. This is
described in a series of articles beginning on p.69 of:
https://worldradiohistory.com/Archive-Company-Publications/Philips-Techn
ical-Review/40s/Philips-Technical-Review-1949.pdf

[Liz Tuddenham]

...This is
https://worldradiohistory.com/Archive-Company-Publications/Philips-Techn
ical-Review/40s/Philips-Technical-Review-1948.pdf

[J. P. Gilliver]

In message <1qgot8k.yqnxuj1vn138mN%***@poppyrecords.invalid.invalid> at
Thu, 7 Sep 2023 12:37:09, Liz Tuddenham

Post by Liz Tuddenham

... The only case I've come across in a TV set
was a little (11"?) dual-standard portable, which had a little D (2V)
valve hidden inside the LOPT casing (DY91 rings a bell?); it had two
(IIRR) turns of thicker wire wound round the LOPT core to drive its
heater.

They were usually EY51 (6.3v heater). They had no base, so the
heater/cathode wires were soldered to the terminals of the LOPT with big
rounded solder blobs to reduce corona discharge. Possibly a DY51, with
lower heater requirements, would have been used in a portable set.

Could have been DY51. From what I remember, it had a plastic base
(possibly just that took wires - I don't think I ever removed the valve
from it to see) and was just floating inside the LOPT can (prevented
from moving by the stiffness of the EHT lead[s]), with the plastic base
having some thickish wires coming out of it that went a couple of times
round the LOPT core - no soldering.

Post by Liz Tuddenham
EY51s were also used in the tripler of the Philips projection
television, immersed in oil and sealed in a metal can. This is
https://worldradiohistory.com/Archive-Company-Publications/Philips-Techn
ical-Review/40s/Philips-Technical-Review-1949.pdf

[tony sayer]

Post by J. P. Gilliver
Thu, 7 Sep 2023 08:56:22, Liz Tuddenham

Post by Liz Tuddenham
[...]

Post by J. P. Gilliver
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.

https://worldradiohistory.com/Archive-Company-Publications/Philips-Techn
ical-Review/40s/Philips-Technical-Review-1949.pdf
"Heating the Filaments of Valves in a Cascade Generator by Means of High
Frequency Current" by Tj. Douma & H.P.J. Brekoo.

Most ingenious! I think only for professional equipment, though. Clever
to pass the h. f. up the same lines as the (presumably mains) frequency
being used to generate the EHT.
Of course, in a TV set the signal being rectified is moderately h. f.
(compared to mains, anyway). The only case I've come across in a TV set
was a little (11"?) dual-standard portable, which had a little D (2V)
valve hidden inside the LOPT casing (DY91 rings a bell?); it had two
(IIRR) turns of thicker wire wound round the LOPT core to drive its
heater. (Very simple valve - about the shape and size of a gherkin; just
a single pin sticking out the top for the EHT, I can't remember what it
had at the base.) I replaced it with a solid-state stick - can't
remember why, I think it became intermittent. (The stick gave a brighter
slightly smaller picture - I presume higher voltage, so brighter and
deflected less.) I never worked on (the EHT part of, anyway) any bigger
set, so I don't know if any used multiple valve rectifiers in a
multiplier arrangement; I'd have thought that would be a complex and
error-prone thing to design and keep going in a domestic setting
(compared to doing it with solid-state stick rectifiers when those
became available), but I could be wrong.

Useful source the Valve museum. They have got the EY and DY wire ended
valves in there and I do remember Selenium rectifiers both mains voltage
and EHT could tell when they failed they simply stunk the house out!..



Http://www.r-type.org/exhib/aaa1233.htm

[Liz Tuddenham]

Post by tony sayer

Post by J. P. Gilliver
Thu, 7 Sep 2023 08:56:22, Liz Tuddenham

Post by Liz Tuddenham
[...]

Post by J. P. Gilliver
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.

https://worldradiohistory.com/Archive-Company-Publications/Philips-Techn
ical-Review/40s/Philips-Technical-Review-1949.pdf
"Heating the Filaments of Valves in a Cascade Generator by Means of High
Frequency Current" by Tj. Douma & H.P.J. Brekoo.

Most ingenious! I think only for professional equipment, though. Clever
to pass the h. f. up the same lines as the (presumably mains) frequency
being used to generate the EHT.
Of course, in a TV set the signal being rectified is moderately h. f.
(compared to mains, anyway). The only case I've come across in a TV set
was a little (11"?) dual-standard portable, which had a little D (2V)
valve hidden inside the LOPT casing (DY91 rings a bell?); it had two
(IIRR) turns of thicker wire wound round the LOPT core to drive its
heater. (Very simple valve - about the shape and size of a gherkin; just
a single pin sticking out the top for the EHT, I can't remember what it
had at the base.) I replaced it with a solid-state stick - can't
remember why, I think it became intermittent. (The stick gave a brighter
slightly smaller picture - I presume higher voltage, so brighter and
deflected less.) I never worked on (the EHT part of, anyway) any bigger
set, so I don't know if any used multiple valve rectifiers in a
multiplier arrangement; I'd have thought that would be a complex and
error-prone thing to design and keep going in a domestic setting
(compared to doing it with solid-state stick rectifiers when those
became available), but I could be wrong.

Useful source the Valve museum. They have got the EY and DY wire ended
valves in there and I do remember Selenium rectifiers both mains voltage
and EHT could tell when they failed they simply stunk the house out!..

There was a story circulating in the late 1960s of a service engineer
who turned up to repair a television set. As the housewife opened the
door he took one sniff, walked back to the van and returned with a
selenium rectifier. He had diagnosed the problem without even entering
the house.

If you want to be reminded of the smell, try sniffing an anti-dandruff
shampoo which contains selenium sulphide.

[tony sayer]

Post by Liz Tuddenham

Post by tony sayer

Post by J. P. Gilliver
Thu, 7 Sep 2023 08:56:22, Liz Tuddenham

Post by Liz Tuddenham
[...]

Post by J. P. Gilliver
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.

https://worldradiohistory.com/Archive-Company-Publications/Philips-Techn
ical-Review/40s/Philips-Technical-Review-1949.pdf
"Heating the Filaments of Valves in a Cascade Generator by Means of High
Frequency Current" by Tj. Douma & H.P.J. Brekoo.

Most ingenious! I think only for professional equipment, though. Clever
to pass the h. f. up the same lines as the (presumably mains) frequency
being used to generate the EHT.
Of course, in a TV set the signal being rectified is moderately h. f.
(compared to mains, anyway). The only case I've come across in a TV set
was a little (11"?) dual-standard portable, which had a little D (2V)
valve hidden inside the LOPT casing (DY91 rings a bell?); it had two
(IIRR) turns of thicker wire wound round the LOPT core to drive its
heater. (Very simple valve - about the shape and size of a gherkin; just
a single pin sticking out the top for the EHT, I can't remember what it
had at the base.) I replaced it with a solid-state stick - can't
remember why, I think it became intermittent. (The stick gave a brighter
slightly smaller picture - I presume higher voltage, so brighter and
deflected less.) I never worked on (the EHT part of, anyway) any bigger
set, so I don't know if any used multiple valve rectifiers in a
multiplier arrangement; I'd have thought that would be a complex and
error-prone thing to design and keep going in a domestic setting
(compared to doing it with solid-state stick rectifiers when those
became available), but I could be wrong.

Useful source the Valve museum. They have got the EY and DY wire ended
valves in there and I do remember Selenium rectifiers both mains voltage
and EHT could tell when they failed they simply stunk the house out!..

There was a story circulating in the late 1960s of a service engineer
who turned up to repair a television set. As the housewife opened the
door he took one sniff, walked back to the van and returned with a
selenium rectifier. He had diagnosed the problem without even entering
the house.
If you want to be reminded of the smell, try sniffing an anti-dandruff
shampoo which contains selenium sulphide.

Yes it did stink how ever we were given a stock of silicon wire ended
diodes these could be wired across the old unit one end left
disconnected..

[J. P. Gilliver]

In message <[e-mail]> at Fri, 8 Sep 2023 14:33:34,
tony sayer <***@bancom.co.uk> writes
[]

Post by tony sayer
Useful source the Valve museum. They have got the EY and DY wire ended
valves in there and I do remember Selenium rectifiers both mains voltage
and EHT could tell when they failed they simply stunk the house out!..
Http://www.r-type.org/exhib/aaa1233.htm

That looks like the one I had, though I think the base was in a white
plastic holder with the heater turns moulded into it. Interesting to see
its absolute maximum was only 15 kV.

[s***@outlook.com]

On Thu, 17 Aug 2023 08:12:29 +0100, Roderick Stewart

Post by Roderick Stewart
On Wed, 16 Aug 2023 15:16:12 +0100, Stephen Wolstenholme

Post by Stephen Wolstenholme
On Wed, 16 Aug 2023 14:37:47 +0100, Roderick Stewart

Post by Roderick Stewart
On Wed, 16 Aug 2023 13:40:32 +0100, Adrian Caspersz

Post by Adrian Caspersz
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!"
http://youtu.be/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.

[Angus Robertson - Magenta Systems Ltd]

Post by s***@outlook.com
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

[Andy Burns]

Post by Angus Robertson - Magenta Systems Ltd

Post by s***@outlook.com
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

[J. P. Gilliver]

Post by Andy Burns

Post by Angus Robertson - Magenta Systems Ltd

Post by s***@outlook.com
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?)

[s***@outlook.com]

On Thu, 17 Aug 2023 15:44:24 +0100, "J. P. Gilliver"

Post by J. P. Gilliver

Post by Andy Burns

Post by Angus Robertson - Magenta Systems Ltd

Post by s***@outlook.com
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.

[Angus Robertson - Magenta Systems Ltd]

Post by s***@outlook.com
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

[Andy Burns]

Post by J. P. Gilliver

Post by Andy Burns

Post by Angus Robertson - Magenta Systems Ltd
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

Post by J. P. Gilliver
(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".

He does a talk about the Eidophor too

[J. P. Gilliver]

Post by Andy Burns

Post by J. P. Gilliver

Post by Andy Burns

Post by Angus Robertson - Magenta Systems Ltd
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

Post by J. P. Gilliver
(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".

[]
Ah. I thought a system had been tried with lasers and a spinning drum
with (presumably) 576 very precisely-angled mirrors. Maybe it was mooted
but modulating the lasers proved problematical.

[Liz Tuddenham]

Post by Angus Robertson - Magenta Systems Ltd

Post by s***@outlook.com
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.

The Eidophor was famed for causing a who-does-not-do-what union dispute
in the BBC. Nobody wanted to work it, the video technicians union
claimed it was lighting and the lighting union claimed it was video.

One of the problems was the ionic bombardment of the cathode, which
could fail randomly (often just before transmission). Spare cathodes
could be swung into place without running down the vacuum, but the whole
cathode assembly would then have to be replaced before it could be used
again. Opening up the tube, replacing the cathodes and then pumping
down to vacuum again took several hours - with the possibility of leaks
each time.

Nobody wanted the responsibility of it failing on transmission.

[J. P. Gilliver]

Post by Roderick Stewart
On Wed, 16 Aug 2023 13:40:32 +0100, Adrian Caspersz

Post by Adrian Caspersz
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!"
http://youtu.be/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).

Post by Roderick Stewart
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.

Post by Roderick Stewart
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.)

Post by Roderick Stewart
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.)

[John Williamson]

Post by Adrian Caspersz

Post by Roderick Stewart
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!"
http://youtu.be/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.

[Brian Gaff]

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
--
--:
This newsgroup posting comes to you directly from...
The Sofa of Brian Gaff...
***@blueyonder.co.uk
Blind user, so no pictures please
Note this Signature is meaningless.!

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

[Max Demian]

Post by Brian Gaff
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.

Some Spectrums had an IC soldered upside down on top of another chip.
Commonly referred to as the "dead cockroach" model.

Post by Brian Gaff
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.

A spot of switch cleaning fluid usually does the trick.

I thought DC through the volume control just caused the crackling rather
than damaging the track, usually found with combined on/off/volume
controls, as there will be a current flowing through the control to
charge the coupling capacitor just after switching on.

Post by Brian Gaff
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

I'm surprised such a thing (a ghetto blaster that plays LPs) existed
after compact cassettes were common (and mostly good quality, especially
the ones you recorded yourself).

[J. P. Gilliver]

[]

Post by Brian Gaff
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

[]
Reminds me of two power supply decisions:

1. The Oric (and I presume the Oric Atmos), mostly TTL logic so needed a
+5 supply: the power supply they provided used a -5 regulator. I don't
know why: I can only guess that the common 7905 regulator was cheaper
than the 7805. It was fine with the basic computer, but got interesting
when you added peripherals, such as the disc drive, which had a beefier
supply, which also powered the computer. (Having said that, I don't
remember it ever actually going wrong.)

2. (Earlier - same company, Tangerine [the Oric said Tangerine on the
PCB].) When the Tangerine came out, the ASTEC modulator (most home
computers then used a domestic TV as monitor, and had to provide RF as
few TVs had baseband input) - little tin box, common on virtually all
home computers! - was initially only available with a 6V rail. Since the
rest of the computer ran on 5V, it would have been tedious to provide a
separate supply just for that - so they designed in a little circuit,
using IIRR the dot clock of 6 MHz (I think the computer ran on 0.75 MHz)
and a teeny inductor: my first experience of a switch-mode supply (only
about 3 components). (FWIW, it seemed to work fine.) [ASTEC subsequently
made the boxes to run on 5V.]

That reminds me - I did hear that one of the other machines around then
(Nascom was it?) was laid out with computer layout software - but that
knew nothing of RF, and they included the modulator in what they gave
it; of course, it never worked, and they had to bodge in an ASTEC tin
box anyway. Whether this is true or not I've no idea.

[Woody]

Post by J. P. Gilliver
[]

Post by Brian Gaff
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

[]
1. The Oric (and I presume the Oric Atmos), mostly TTL logic so needed a
+5 supply: the power supply they provided used a -5 regulator. I don't
know why: I can only guess that the common 7905 regulator was cheaper
than the 7805. It was fine with the basic computer, but got interesting
when you added peripherals, such as the disc drive, which had a beefier
supply, which also powered the computer. (Having said that, I don't
remember it ever actually going wrong.)
2. (Earlier - same company, Tangerine [the Oric said Tangerine on the
PCB].) When the Tangerine came out, the ASTEC modulator (most home
computers then used a domestic TV as monitor, and had to provide RF as
few TVs had baseband input) - little tin box, common on virtually all
home computers! - was initially only available with a 6V rail. Since the
rest of the computer ran on 5V, it would have been tedious to provide a
separate supply just for that - so they designed in a little circuit,
using IIRR the dot clock of 6 MHz (I think the computer ran on 0.75 MHz)
and a teeny inductor: my first experience of a switch-mode supply (only
about 3 components). (FWIW, it seemed to work fine.) [ASTEC subsequently
made the boxes to run on 5V.]
That reminds me - I did hear that one of the other machines around then
(Nascom was it?) was laid out with computer layout software - but that
knew nothing of RF, and they included the modulator in what they gave
it; of course, it never worked, and they had to bodge in an ASTEC tin
box anyway. Whether this is true or not I've no idea.

-5V was probably to work RS232 with +5V from elsewhere.

[J. P. Gilliver]

[]

Post by Woody

Post by J. P. Gilliver
1. The Oric (and I presume the Oric Atmos), mostly TTL logic so
needed a +5 supply: the power supply they provided used a -5
regulator. I don't know why: I can only guess that the common 7905
regulator was cheaper than the 7805. It was fine with the basic
computer, but got interesting when you added peripherals, such as the
disc drive, which had a beefier supply, which also powered the
computer. (Having said that, I don't remember it ever actually going wrong.)

[]

Post by Woody
-5V was probably to work RS232 with +5V from elsewhere.

No, I can't remember whether it even _had_ a serial port - I think not.
What I mean is, it had a 7905 (-5V) regulator to supply the main +5V for
the computer. So ground wasn't, as it were.