OK, whether the field is retiring me or the other way around is
irrelevent. But I have been pretty much the foremost expert on three
tube PTVs in at least this state for some time. Of course you see that
is not exactly the hottest job in town. I am not saying that I am THE
expert on everything, but what makes a CRT RPTV work, as opposed to a
direct view, that has been my specialty. In fact if I went to work on
direct views I would probably have to work for ten bucks an hour.

But I get into theory and this thread is for folks like that. I know
what it takes to make those things work, I have worked damnear
miracles on them, but I never designed them. I have done some repairs
so serious that I guess I could claim I can build one, but I still
never designed one.

A couple months ago I ran into one of those Hitachis with the necked
down neck. I mean where the yoke goes the neck is narrower, which
means the yoke is manufactured on the tube and is TRULY a bonded yoke.
Not just glued like before.

They did this of course to get the coils closer to the beam, which
increases deflection efficiency. So one can only assume that the power
consumed by the deflection circuit was an issue to be addressed. Since
I am a million years old I remember when the old delta gun CRTs went
out and the inline guns came in, and then smaller and smaller necks.
Inverse square folks, the closer the better.

Now MY question :

Why the hell didn't they just go with electrostatic deflection like in
a scope ?

Think about it, you people out there who know engineering, think about
it. Why not ? I understand about the CRT parameters and the variance
with beam current and I also know about beam density. I know these are
all problems, but using magnetic deflection solved none of them !

THINK THINK about that.

OK, I am not an idiot, I KNOW why a color CRT whether it is delta or
inline gun, would not benefit from electrostatic deflection. But I see
no disadvantabe when it comes to a monochrome CRT, which is what the
scope was. And what the PTV was as well.

You can use magnetic deflection for a scope, it's just that the
results suck. Bandwidth and all that. But in a three tube PTV that
flexibility in the deflection would be so much more efficient. You got
horizontal, vertical, and SIX channels of amps running sub yokes. I
thought the wattage race had already started. This would have won.

But I am also not stupid. If they could be more efficient it would
have been a selling point. No STKs, small transistors work into the IE
capacitance of the plates. That's all. You could concievably have the
impossible (OK I know osmeone will find one), the old never happen CRT
based 1080p TV.

The reason you can't have a CRT at 1080p is because of the inductance
of the yoke. You would have to stick a four thousand volt pulse to
it.

But you do not have that problem with deflection plates, rather than
coils.

In the end, what seems to elude me is why they did not persue
electrostatic deflection for three tube PTVs. they have all the
halation and every other thing figured out, tracking HV/focus levels
and all that already.

Or did they just want to sell yokes ? :-)

J

On May 1, 2:47*am, Jeff Urban wrote:
...snip...
Why the hell didn't they just go with electrostatic deflection like in
a scope ?

Think about it, you people out there who know engineering, think about
it. Why not ? I understand about the CRT parameters and the variance
with beam current and I also know about beam density. I know these are
all problems, but using magnetic deflection solved none of them !

THINK THINK about that.

...snip....

Magnetic deflection can bend the beam at a sharper angle than the
electrostatic deflection.

Look inside an old Tektronix scope, which uses electrostatic
deflection. That neck is LONG because the angle of deflection for
physically realizable voltages is so small.

On May 1, 5:25*am, Robert Macy wrote:
On May 1, 2:47*am, Jeff Urban wrote:

...snip...
Why the hell didn't they just go with electrostatic deflection like in
a scope ?

Think about it, you people out there who know engineering, think about
it. Why not ? I understand about the CRT parameters and the variance
with beam current and I also know about beam density. I know these are
all problems, but using magnetic deflection solved none of them !

THINK THINK about that.

...snip....

Magnetic deflection can bend the beam at a sharper angle than the
electrostatic deflection.

Look inside an old Tektronix scope, which uses electrostatic
deflection. That neck is LONG because the angle of deflection for
physically realizable voltages is so small.

Forgot to mention the obvious:
The required Electrostatic deflection voltage goes UP as the HV goes
up, because the electron spends less time in the gradient between the
plates

Anybody out there confirm the following statement?
In contrast, the required Magnetic deflection goes DOWN as the HV goes
up because the electron is moving faster through the field and gets
'bent' more.

Robert Macy writes:

On May 1, 5:25*am, Robert Macy wrote:
On May 1, 2:47*am, Jeff Urban wrote:

...snip...
Why the hell didn't they just go with electrostatic deflection like in
a scope ?

Think about it, you people out there who know engineering, think about
it. Why not ? I understand about the CRT parameters and the variance
with beam current and I also know about beam density. I know these are
all problems, but using magnetic deflection solved none of them !

THINK THINK about that.

...snip....

Magnetic deflection can bend the beam at a sharper angle than the
electrostatic deflection.

Look inside an old Tektronix scope, which uses electrostatic
deflection. That neck is LONG because the angle of deflection for
physically realizable voltages is so small.

Forgot to mention the obvious:
The required Electrostatic deflection voltage goes UP as the HV goes
up, because the electron spends less time in the gradient between the
plates

Anybody out there confirm the following statement?
In contrast, the required Magnetic deflection goes DOWN as the HV goes
up because the electron is moving faster through the field and gets
'bent' more.

Nope.

--
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Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
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| Mirror Sites: http://www.repairfaq.org/REPAIR/F_mirror.html

Important: Anything sent to the email address in the message header above is
ignored unless my full name AND either lasers or electronics is included in the
subject line. Or, you can contact me via the Feedback Form in the FAQs.

(Samuel M. Goldwasser) wrote in
:

Robert Macy writes:

On May 1, 5:25*am, Robert Macy wrote:
On May 1, 2:47*am, Jeff Urban wrote:

...snip...
Why the hell didn't they just go with electrostatic deflection
like in a scope ?

Think about it, you people out there who know engineering, think
about it. Why not ? I understand about the CRT parameters and the
variance with beam current and I also know about beam density. I
know these are all problems, but using magnetic deflection solved
none of them !

THINK THINK about that.

...snip....

Magnetic deflection can bend the beam at a sharper angle than the
electrostatic deflection.

Look inside an old Tektronix scope, which uses electrostatic
deflection. That neck is LONG because the angle of deflection for
physically realizable voltages is so small.

and with a long neck and electrostatic deflection,the CRT was amazingly
sensitive to Earth's magnetic field,thus requiring shielding.
Telequipment scopes were infamous for their poor trace rotation
calibration,they would never hold the setting.Move the scope,and you had to
readjust the TR.

Forgot to mention the obvious:
The required Electrostatic deflection voltage goes UP as the HV goes
up, because the electron spends less time in the gradient between the
plates

it depends on the electron gun structure.
the TEK 2465 tube had specially constructed deflection plates and a
focusing "lens" instead of the mesh lens typically used. It was designed to
use low deflection voltages that could be provided by hybrid ICs instead of
discrete defl.amps with HV transistors. the 2465 tube was fairly short,too.
I used to have a booklet that described the CRT tech for the 2465 tube,lost
it when the Orlando Service center was shut down.

Alas,all that technology is gone now.TEK no longer makes it's own CRTs.


Anybody out there confirm the following statement?
In contrast, the required Magnetic deflection goes DOWN as the HV
goes up because the electron is moving faster through the field and
gets 'bent' more.

Nope.


I fail to see how a "faster" E-beam will bend more under magnetic
fields,but not under electrostatic fields.

--
Jim Yanik
jyanik
at
localnet
dot com

Jeff Urban wrote:

OK, whether the field is retiring me or the other way around is
irrelevent. But I have been pretty much the foremost expert on three
tube PTVs in at least this state for some time. Of course you see that
is not exactly the hottest job in town. I am not saying that I am THE
expert on everything, but what makes a CRT RPTV work, as opposed to a
direct view, that has been my specialty. In fact if I went to work on
direct views I would probably have to work for ten bucks an hour.

But I get into theory and this thread is for folks like that. I know
what it takes to make those things work, I have worked damnear
miracles on them, but I never designed them. I have done some repairs
so serious that I guess I could claim I can build one, but I still
never designed one.

A couple months ago I ran into one of those Hitachis with the necked
down neck. I mean where the yoke goes the neck is narrower, which
means the yoke is manufactured on the tube and is TRULY a bonded yoke.
Not just glued like before.

They did this of course to get the coils closer to the beam, which
increases deflection efficiency. So one can only assume that the power
consumed by the deflection circuit was an issue to be addressed. Since
I am a million years old I remember when the old delta gun CRTs went
out and the inline guns came in, and then smaller and smaller necks.
Inverse square folks, the closer the better.

Now MY question :

Why the hell didn't they just go with electrostatic deflection like in
a scope ?

Think about it, you people out there who know engineering, think about
it. Why not ? I understand about the CRT parameters and the variance
with beam current and I also know about beam density. I know these are
all problems, but using magnetic deflection solved none of them !

THINK THINK about that.

OK, I am not an idiot, I KNOW why a color CRT whether it is delta or
inline gun, would not benefit from electrostatic deflection. But I see
no disadvantabe when it comes to a monochrome CRT, which is what the
scope was. And what the PTV was as well.

You can use magnetic deflection for a scope, it's just that the
results suck. Bandwidth and all that. But in a three tube PTV that
flexibility in the deflection would be so much more efficient. You got
horizontal, vertical, and SIX channels of amps running sub yokes. I
thought the wattage race had already started. This would have won.

But I am also not stupid. If they could be more efficient it would
have been a selling point. No STKs, small transistors work into the IE
capacitance of the plates. That's all. You could concievably have the
impossible (OK I know osmeone will find one), the old never happen CRT
based 1080p TV.

The reason you can't have a CRT at 1080p is because of the inductance
of the yoke. You would have to stick a four thousand volt pulse to
it.

But you do not have that problem with deflection plates, rather than
coils.

In the end, what seems to elude me is why they did not persue
electrostatic deflection for three tube PTVs. they have all the
halation and every other thing figured out, tracking HV/focus levels
and all that already.

Or did they just want to sell yokes ? :-)

J

Electrostatic deflection is fast, which is why it was used in CRT
scopes. However, the spot size is the pits by comparison--magnetic
deflection and magnetic focusing gives a much, much sharper spot.

Cheers

Phil Hobbs
--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510
845-480-2058

hobbs at electrooptical dot net
http://electrooptical.net

In article
,
Jeff Urban wrote:

OK, whether the field is retiring me or the other way around is
irrelevent. But I have been pretty much the foremost expert on three
tube PTVs in at least this state for some time. Of course you see that
is not exactly the hottest job in town. I am not saying that I am THE
expert on everything, but what makes a CRT RPTV work, as opposed to a
direct view, that has been my specialty. In fact if I went to work on
direct views I would probably have to work for ten bucks an hour.

But I get into theory and this thread is for folks like that. I know
what it takes to make those things work, I have worked damnear
miracles on them, but I never designed them. I have done some repairs
so serious that I guess I could claim I can build one, but I still
never designed one.

A couple months ago I ran into one of those Hitachis with the necked
down neck. I mean where the yoke goes the neck is narrower, which
means the yoke is manufactured on the tube and is TRULY a bonded yoke.
Not just glued like before.

They did this of course to get the coils closer to the beam, which
increases deflection efficiency.

Probably, they did it to get precisely the alignment they needed, to
make it the same between the tubes of a set, and to keep it that way.
For one thing, it makes replacing a CRT a whole lot less finicky.

Now MY question :

Why the hell didn't they just go with electrostatic deflection like in
a scope ?

Think about it, you people out there who know engineering, think about
it. Why not ? I understand about the CRT parameters and the variance
with beam current and I also know about beam density. I know these are
all problems, but using magnetic deflection solved none of them !

-- snip --

The insurmountably serious problem with electrostatic deflection is
astigmatism, and my understanding that there is in fact no way to solve
it.

Recall that the "beam" is really not a pencil like it's usually shown in
drawings; it's a pair of narrow cones, base to base, with one of the
points at the cathode and the other at the screen. Focusing the beam is
actually forming an image of the cathode on the screen. The Largest
diameter of the beam occurs wherever the focusing electrode (or coil)
is, but the beam still has a substantial diameter when it passes the
deflection plates.

When the beam is electrostatically deflected, the various electrons of
the beam are affected differently depending on where they are in the
beam, and the strength of the electric field between the plates (and
this changes during the deflection process). This causes the image to
become de-focused and elongated in one dimension. This distortion cannot
be pre-corrected by any sort of electron-optical mechanism. The same
thing happens when the beam passes through the second set of plates,
too, of course. The result is that the spot size and shape can be fine
in the center of the screen, but pretty poor at the edges, and
*terrible* in the corners.

O-scopes have long tubes to minimize the deflection angle, *not* because
high-angle deflection is especially difficult, but to minimize the
astigmatism problem, which gets worse very quickly as the deflection
angle increases beyond a few degrees.

Electrostatic deflection, unlike magnetic, involves a transfer of
momentum to the beam (put another way, electrostatic deflection works by
accelerating the electrons sideways as they pass between the plates, but
when an electron beam is bent by a magnet, the beam doesn't "notice"
that it's being bent, sort of like going around a properly canted curve
in a fast car).

The reason you can't have a CRT at 1080p is because of the inductance
of the yoke. You would have to stick a four thousand volt pulse to
it.

Actually, no. There have been many CRTs with that and higher resolution
used with computers and in high-quality imaging systems. Especially with
transistors, very high currents are no problem, and those systems can
incorporate very low inductance yokes; recall that it's amps times turns
that determines the field strength. Some years ago, I was involved with
a CRT-based system that got an honest 4096x4096 pixel resolution out of
a nearly standard 5" CRT. It used magnetic deflection; we never could
have done it with an electrostatic jug.

--

If you want to take a look at a truly *bizarre* video projection
technique, find out how an Eidophor works. Or worked; I really don't
know if they're in business these days. Think about vacuum pumps,
rotating oil-covered mirrors, Schlerin optical systems, ten-kilowatt
xenon short-arc lamps, and little air-locks for replacing the filaments
while in operation, all in one box. Times three, of course, for color.

Isaac

If you want to take a look at a truly *bizarre* video projection
technique, find out how an Eidophor works. Or worked; I really
don't know if they're in business these days. Think about vacuum
pumps, rotating oil-covered mirrors, Schlerin optical systems,
ten-kilowatt xenon short-arc lamps, and little air-locks for
replacing the filaments while in operation, all in one box. Times
three, of course, for color.

Actually, I think Eidophor color used a rotating wheel.

The Eidophor system is more than 50 years old. GE glommed onto it back in
the 70s (I believe), and produced a very compact projection system (far
smaller than the original), though I don't know if it was commercially
successful. GE also designed a video recording system -- "photoplastic
recording" -- that froze the Eidophor ripples on a moving strip of plastic.
It was never commercialized.

On May 1, 3:27*pm, Jim Yanik wrote:

I fail to see how a "faster" E-beam will bend more under magnetic
fields,but not under electrostatic fields.

--
Jim Yanik
jyanik
at
localnet
dot com

You're right. The beam, doesn't get bent more it gets bent less.
That's why CRT TVs bloom when the APL goes up. More beam current,
drooping EHT, beam slows down and spends more time in the deflection
field, bends more and the picture gets bigger. Down with CRTs. May
they rot in the landfill. May we have something with as good color
though?

G²

I think most of the explanations given here are dead wrong, but it's been a
while since I've studied this stuff, and I don't want to get into it too
deeply.

On Wed, 2 May 2012 01:26:50 -0700, "William Sommerwerck"
wrote:

If you want to take a look at a truly *bizarre* video projection
technique, find out how an Eidophor works. Or worked; I really
don't know if they're in business these days. Think about vacuum
pumps, rotating oil-covered mirrors, Schlerin optical systems,
ten-kilowatt xenon short-arc lamps, and little air-locks for
replacing the filaments while in operation, all in one box. Times
three, of course, for color.

Actually, I think Eidophor color used a rotating wheel.

The Eidophor system is more than 50 years old. GE glommed onto it back in
the 70s (I believe), and produced a very compact projection system (far
smaller than the original), though I don't know if it was commercially
successful. GE also designed a video recording system -- "photoplastic
recording" -- that froze the Eidophor ripples on a moving strip of plastic.
It was never commercialized.



GE, just before they closed their own television factories in the mid
80s, planned to bring out a home rear projection television using the
oil technology. The techs, at a training seminar for one of their
other chassises, were told that we should sign up for a training
session 6 months hence. The Roanoke factory was closed before the
seminar was scheduled. Chuck-

In article ,
"William Sommerwerck" wrote:

If you want to take a look at a truly *bizarre* video projection
technique, find out how an Eidophor works. Or worked; I really
don't know if they're in business these days. Think about vacuum
pumps, rotating oil-covered mirrors, Schlerin optical systems,
ten-kilowatt xenon short-arc lamps, and little air-locks for
replacing the filaments while in operation, all in one box. Times
three, of course, for color.

Actually, I think Eidophor color used a rotating wheel.

There were both kinds: a monochrome one with a wheel (mostly for
computer output purposes), and a three-beam one -- R, G, B -- which
worked better for "regular" TV.

The three-color ones were capable of producing a 65-foot-diagonal image
in which you could see the NTSC color subcarrier crawling up the screen
(demonstrating really good bandwidth and focus). They were also the only
imaging devices of that time that could properly display the "I" and "Q"
bars of a composite color bar test pattern. That was because the light
source was a full-spectrum arc, and dichroic filters were used to
separate the primaries, so it was possible to select the three primary
colors with great precision (you can't do that if you start with
phosphors).

Isaac (who once made an emergency air trip from LA to Houston because
somebody had let one of the dumpster-sized things swing 30' into a
concrete wall while it was being hoisted into place)

Jeff Urban wrote:


Why the hell didn't they just go with electrostatic deflection like in
a scope ?

You need quite a lot of voltage to swing the beam. Vertical is
not so tough, but a linear amp to swing maybe 500+ Volts at
horizontal frequency and have high enough bandpass for the horizontal
retrace is ALSO going to burn a good deal of power. The
magnetic sweep system is mostly a switching power supply, and
so gets a good reduction in power dissipation that way.

Jon

Robert Macy wrote:



Forgot to mention the obvious:
The required Electrostatic deflection voltage goes UP as the HV goes
up, because the electron spends less time in the gradient between the
plates

Right, in the high-end Tek scopes, they had a tapped delay line
inside the CRT, and so the deflection voltage followed the beam as
it shot toward the screen. That should tell you the time spent between
the deflection plates is in the tens of ns!

Anybody out there confirm the following statement?
In contrast, the required Magnetic deflection goes DOWN as the HV goes
up because the electron is moving faster through the field and gets
'bent' more.

Umm, no, I don't think so. But, I'm not a whiz at electrodynamics.

Jon

Jon Elson wrote:

Jeff Urban wrote:

Why the hell didn't they just go with electrostatic deflection like in
a scope ?

You need quite a lot of voltage to swing the beam. Vertical is
not so tough, but a linear amp to swing maybe 500+ Volts at
horizontal frequency and have high enough bandpass for the horizontal
retrace is ALSO going to burn a good deal of power. The
magnetic sweep system is mostly a switching power supply, and
so gets a good reduction in power dissipation that way.

Jon

Early TVs did use electrostatic deflection, but the beam quality (and
hence the spot size) is far better with magnetic.

Cheers

Phil Hobbs
--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510
845-480-2058

hobbs at electrooptical dot net
http://electrooptical.net

On Tuesday, May 1, 2012 3:27:46 PM UTC-7, Jim Yanik wrote:
(Samuel M. Goldwasser) wrote in
:

Robert Macy writes:

On May 1, 5:25*am, Robert Macy wrote:
On May 1, 2:47*am, Jeff Urban wrote:

...snip...
Why the hell didn't they just go with electrostatic deflection
like in a scope ?

I fail to see how a "faster" E-beam will bend more under magnetic
fields,but not under electrostatic fields.

The transverse momentum you get from electrostatic deflection is
proportional to deflection plate voltage. The longitudinal momentum is
proportional to accelerating voltage (for color phosphors, 25 kV typical).
So, tangent of deflection angle is at most Vdeflection/Vacceleration.
Even infinite deflection voltage only gets 90 degrees deflection.

For magnetic deflection, the beam acquires a curvature proportional to B field;
the deflection angle can be anything you want. When it gets to 360 degrees,
your tube becomes a 'cyclotron'. I've seen multigigavolt beams doing
loops, at near the speed of light, for hours. You can't do that with electrostatic
deflection.
you can get any deflection you want, no limit

whit3rd wrote:

On Tuesday, May 1, 2012 3:27:46 PM UTC-7, Jim Yanik wrote:
(Samuel M. Goldwasser) wrote in
:

Robert Macy writes:

On May 1, 5:25 am, Robert Macy wrote:
On May 1, 2:47 am, Jeff Urban wrote:

...snip...
Why the hell didn't they just go with electrostatic deflection
like in a scope ?

I fail to see how a "faster" E-beam will bend more under magnetic
fields,but not under electrostatic fields.

The transverse momentum you get from electrostatic deflection is
proportional to deflection plate voltage. The longitudinal momentum is
proportional to accelerating voltage (for color phosphors, 25 kV typical).
So, tangent of deflection angle is at most Vdeflection/Vacceleration.
Even infinite deflection voltage only gets 90 degrees deflection.

For magnetic deflection, the beam acquires a curvature proportional to B field;
the deflection angle can be anything you want. When it gets to 360 degrees,
your tube becomes a 'cyclotron'. I've seen multigigavolt beams doing
loops, at near the speed of light, for hours. You can't do that with electrostatic
deflection.
you can get any deflection you want, no limit

Also, electrostatic deflection defocuses and aberrates the beam, whereas
magnetic doesn't.

Cheers

Phil Hobbs
--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510
845-480-2058

hobbs at electrooptical dot net
http://electrooptical.net