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The Secret Lifetime of XY Screens

The Secret Lifetime of XY Screens

2024-03-11 09:42:48






The Secret Lifetime of XY Screens


 

The Secret Lifetime of XY Screens

By Jed Margolin


      Throughout my time at Atari/Atari Video games I
labored on a number of XY video games. This text represents what I learn about XY
Screens. XY was Atari’s title for what the Laptop Graphics trade calls
‘”Random Scan” and the Video Sport Group calls “Vector Video games.” The main
elements of the XY Monitor are the Cathode Ray Tube (CRT), the Deflection
Amplifiers, and the Excessive Voltage Provide.

 

XY Screens – Contents

1. CRT Electron Optics

2. Deflection Sorts

    A. Electrostatic

    B. Magnetic

3. XY – Deflection Amplifiers

4. High Voltage Supplies

5. Screen Phosphors

6. Color CRTs

7. Alternatives

8. References





CRT Electron Optics


The CRT is an evacuated container with an Electron Gun that shoots a
targeted electron beam at a phosphor-coated display screen which absorbs the power
of the electrons and re-emits it as seen gentle. The Excessive Voltage Provide
produces the voltage wanted to speed up the electron beam towards the
display screen. The Deflection Amplifiers transfer the electron beam within the desired
sample.

We are going to begin with the CRT proven in Determine 1.

When metallic is heated to incandescence in a vacuum the electrons close to
the floor are given sufficient power to fly off into the encompassing house.

The Electron Gun begins with the Heater (or Filament) which makes use of an
electrical present in an effort to warmth it as much as incandescence. Nevertheless, as an alternative
of utilizing the Heater  to immediately produce electrons, it heats up a
separate factor, the Cathode, to supply the electrons. One purpose for
doing it this fashion is that it permits the Heater provide to be electrically
remoted from the Cathode.  This retains the Cathode voltage out of
the Heater provide, permitting it for use for different issues as nicely. It is
additionally a security subject, because the Cathode voltage may be substantial. I
suspect that another excuse for utilizing an not directly heated cathode is that
it permits the Heater to be optimized for  lengthy life and the Cathode
optimized for emitting electrons.


The Management Grid (known as G1) is operated with a detrimental bias with respect
to the Cathode (sometimes round 50V.) and acts to repel the electrons
coming from the Cathode.

The rationale for doing that is that the Display Grid (G2) is operated at
a voltage that’s greater than the Cathode (sometimes a number of hundred volts).
The physics works out {that a} small change within the Management Grid voltage has
a big impact on the electron beam present.

The electron beam is additional accelerated by Focus Grid (G3) which is
operated at an excellent greater voltage (sometimes a number of thousand volts).
As you might have guessed, the Focus Grid additionally focuses the beam.

The ultimate acceleration comes from an excellent greater voltage on the Anode
(sometimes a number of instances the voltage on the Focus Grid).

The ensuing beam strikes the phosphor-covered display screen which absorbs
the power of the electrons and re-emits it as seen gentle

The equations that describe the movement of electrons in a possible area
take the identical kind as these used to explain the habits of optical lenses.
The form of the electron beam on the display screen is a picture of the electron
beam at what is named the crossover level, which is the place within the electron
gun the place the grids trigger the electrons  to alter velocity. 
The ratio of the voltage on the Focus Grid (G3) relative to the voltage
on the Anode controls the crossover level and subsequently the purpose at which
the picture is concentrated, a lot the identical method because the curvature of an optical
lens determines its focus.

Because of this it’s known as electron optics.

 An extra notice concerning the grid constructions. Whereas customary vacuum
tubes (each receiving and transmitting sorts) use grids within the type of
a mesh, the grids in a CRT are cylinders.  As well as, the Management
Grid (G1) additionally incorporates a disk with a gap within the center known as the Aperture
Disk. ( See Determine 2). This helps produce a slender electron beam


Now that we’ve got a pleasant targeted electron beam hitting the phosphor we
ought to in all probability transfer it round earlier than we burn the display screen.





Electrostatic Deflection


Two pairs of parallel plates are mounted within the CRT. A voltage utilized
throughout the Vertical Plates will deflect the electron beam vertically as
proven in Determine 3. A voltage utilized throughout the Horizontal Plates will
deflect the electron beam horizontally.  (One of many Horizontal Plates
in Determine 3 is hidden by its mate.)


The deflection of the beam in an electrostatically deflected CRT is
given (from Whitaker) by:

                
Vd * dl


    tan(da) =  ____________

              
2 * dp * Vb


 

the place     Vd = the voltage between the
deflection plates

              
dl =  the size of the plates

              
dp = the gap between the plates

              
Vb = beam voltage


For the reason that building of the plates (dl and dp) is set by the CRT
producer we are going to simplify issues by letting   K1 = 
dl/(2*dp)   in order that:

    tan(da) = K1 * Vd / Vb

Due to this fact, the tangent of the deflection angle is proportional to the
voltage between the plates and inversely proportional to the beam voltage
(Anode voltage).

From Determine 3:

    tan(da) = db/L

L is one other worth decided by the CRT producer, in order that the deflection
of the beam is given by:

    db = K2 * Vd / Vb      
the place K2 = L * dl/(2*dp)

The excellent news is that the display screen deflection of the beam is proportional
to the voltage between the plates.

The unhealthy information is that it’s inversely proportional to the Anode voltage.
Which means if we double the Anode voltage we’ve got to double the voltage
between the plates for a similar beam deflection. If the voltage between
the deflection plates is already 200V, then we would want to extend it
to 400V for a similar deflection. Though that may not be an excessive amount of of
an issue with at this time’s elements, the deflection amplifiers would now
additionally require twice the slew price if we’re to maneuver the beam on the similar
velocity.

Why not simply use a low Anode voltage?

First, Anode voltages must be excessive simply to get acceptable display screen
brightness.

And second, the Anode voltage has an impact on the beam focusing. 
Because the Anode voltage is elevated, the electron beam may be targeted to
a smaller spot dimension.

For these causes, electrostatic CRTs are used principally in oscilloscopes
the place velocity is essential and screens are small.





 Magnetic Deflection


   An electron beam is deflected when it strikes by means of 
a magnetic area. In a CRT with magnetic deflection, as an alternative of two pairs
of deflection plates contained in the CRT, there are two pairs of deflection
coils mounted across the neck. The 2 pairs of coils are mounted- at proper
angles to supply X and Y deflection. As a facet notice, an electron beam
is deflected at proper angles to the utilized magnetic area, in order that the
coils which are mounted on both facet of the neck (horizontally) deflect
the beam vertically; the coils which are mounted vertically deflect the
beam horizontally.


The deflection of the beam is given (from Whitaker) by the components:

    sin(da) = (2.97*10**5) * L *
Bm / (V**0.5)

Let’s simplify it by letting K3 = (2.97*10**5) * L,  in order that

    sin(da) = K3 * Bm / (V**0.5)

    the place:

                 
Bm is the magnetic area

                 
V is the Anode voltage

Additional, in a correctly designed coil, the magnetic area (Bm) is proportional
to the electrical present within the yoke coils so we will say:

    sin(da) = K4 * I / (V**0.5)

Once more, there’s excellent news and unhealthy information.

The excellent news is that the deflection is proportional to the inverse
sq. root of the Anode voltage, versus the straight inverse in
the electrostatic CRT. Which means if we double the Anode voltage we
solely have to extend the yoke present by an element of 1.414 . (The electron
optics relating Anode voltage to identify dimension are the identical as for the electrostatic
CRT. The next Anode voltage produces a smaller spot dimension.)

The unhealthy information is that the deflection on the display screen (db) goes to be
the tangent of the arcsin of the yoke present. You’ll be able to see that is Determine
4 the place

    tan(da) = db/L

in order that

    db = L * tan(da)

For angles of lower than 30 levels, sin(angle) is roughly equal
to the angle in radians. That is proven in Determine 5.

Likewise, for angles of lower than 30 levels, tan(angle) is roughly
equal to the angle in radians. That is proven in Determine 6.


If we preserve our deflection angle lower than 30 levels we’ll be okay. That
would imply utilizing a 60 diploma CRT (plus and minus 30 levels).

Sadly, that was not a normal kind for the sizes we needed
to make use of (13″, 19″, and later, 25″). The best way CRTs had been made (and doubtless
nonetheless are) is that every year Corning guessed what number of CRTs the TV trade
would want for the subsequent 12 months. They’d then construct that many CRT envelopes
in a single run, and that may be it for the 12 months. The CRT envelopes had been
then bought to the CRT producers. Corning will need to have been good at estimating
the necessity as a result of I do not keep in mind there ever being a CRT scarcity.

Commonplace CRTs are available 90 diploma, 100 diploma, and 110 diploma deflection
angles. It’s because the bigger the deflection angle, the shorter the
CRT envelope. These deflection angles took place as a result of folks don’t desire
the backs of their TVs to stay out lots.

Due to this fact, for a 90 diploma (or extra) CRT we’ve got to cope with the deflection
nonlinearity.

The deflection nonlinearity is definitely worse than you would possibly suppose and
is completely the fault of geometry. The reason being that there’s just one
electron beam, and it could solely be deflected at one angle at a time.

Determine 7a represents the geometry of a beam aimed on the heart of the
display screen. The face of the display screen is proven in Determine 7b.


If we deflect the beam alongside solely the X axis (Determine 8a) the deflection
angle to supply a display screen deflection of dx will probably be atan(dx/L).


Nevertheless, as proven in Determine 9, if we need to produce a deflection of
each X and Y axes (dx and dy respectively) , the deflection angle will
be atan(dr/L). Since dr is bigger than both dx or dy, the deflection
angle may even be bigger.


This can be a drawback, particularly on the corners of the display screen the place the
deflection angles are the most important. Bear in mind Determine 6. The bigger the deflection
angle, the farther we’re working within the nonlinear a part of the tangent
operate.

You’ll have heard of pincushion distortion. Now you realize what causes
it.

Determine 10 exhibits the uncorrected distortion for a 60 diploma CRT.

Determine 11 exhibits how a lot worse it’s for a 90 diploma CRT.


There may be a further issue that causes geometric distortion.

Thus far, our analyses have assumed a superbly flat display screen. Whereas CRTs
with completely flat screens can be found at this time, they weren’t obtainable
within the Eighties. This was earlier than even almost-flat screens. On this one we
will omit the maths and simply present Determine 12.


The rationale for the curved display screen is that curved screens are higher ready
to face up to the big forces produced by the vacuum contained in the envelope.
In spite of everything, this can be a vacuum tube.

Now that we’ve got proven the causes of pincushion distortion, what are
we going to do about it?

Based on Grob (web page 220):

“For monochrome image tubes, the pincushion distortion is
corrected by everlasting magnets mounted on the housing of the deflection
yoke. These pincushion magnets can’t be used with shade image tubes,
nevertheless, as a result of they’d have an effect on the three beams by completely different quantities,
leading to extra issues with shade purity and convergence. Due to this fact,
dynamic pincushion correction is used with shade image tubes.”


Certainly, the Electrohome GO5 Monochrome X-Y Monitor (“Quadrascan”) used
in Lunar Lander, BattleZone, and Crimson Baron used magnets on the yoke housing
to supply pincushion distortion.

Based on Whitaker (web page 234):

“Pincushion  correction is utilized in all wide-angle deflection
techniques. This correction could also be achieved by one of many following”


A particular yoke design that has managed area distortion.

Predistorting the deflection present and making use of it to a separate pincushion
transformer that connects the correction present to the vertical yoke.”


Whitaker’s reference to a pincushion transformer exhibits an apparent bias
towards raster scan shows. An XY show would use a circuit to predistort
the deflection currents.

Additionally keep in mind that the Grob reference is from 1975. Maybe the
technique of utilizing particular yoke design to supply a managed distortion
to supply pincushion got here later.

Usually, pincushion correction is carried out within the monitor. Nevertheless,
Atari’s first shade XY video games (Tempest, Area Duel, Gravitar, and Black
Widow) did pincushion correction on the sport board.

This is the way it was finished.


Now you realize what the MC1495 analog multipliers had been for.

The next is a extra full schematic of the circuit.

In Atari’s final shade XY video games (Star Wars and Main Havoc) pincushion
correction was finished within the monitor utilizing a specifically designed yoke.





XY Deflection Amplifiers


We have now gotten to the purpose the place the currents within the X and Y deflection
coils will transfer the electron beam across the display screen in a linear style.

Now we’ve got to supply the present.

For the reason that output of the Vector Generator will probably be a voltage the Deflection
Amplifier will convert a voltage to a present (which will probably be substantial). 
To do that would require a foray into Management Idea.

A normal suggestions management community has the next kind:


The Gyrator takes the distinction between the optimistic and detrimental inputs
and produces output Y.

The Achieve Block amplifies its enter Y by an element of A to supply output
Vout.

Output Vout is fed again to the detrimental enter of the Gyrator utilizing Switch
Operate H.

Now some simple arithmetic.

    Y = Vin - Vout * H

    Vout = A * Y

Due to this fact:

    Vout = A * Y

        
= A * (Vin - Vout*H)


        
= A * Vin - A*Vout*H

    Vout + A*Vout*H = A*Vin

    Vout *(1+A*H) = A*Vin

           
A*Vin


    Vout = --------

         
(1 + A*H)

              
Vin


    Vout =  ---------           

Equation 1


           
(1/A + H)


 

If A is sufficiently giant, 1/A = 0, in order that

    Vout = Vin/H                

Equation 2

The following factor is to note that the Gyrator and Achieve Block in Determine
14 appears lots like an Op-Amp. The  primary distinction is that Output
Y is just not usually accessible. (That is okay, Output Y has served its goal.)


Let’s strive a Switch Operate H within the type of a easy resistor divider
the place

    H = R1/(R1+R2)

 

 


From Equation 2:

    Vout = Vin * 1/H

        
= Vin *    1


                
----------


                
R1/(R1+R2)

        
= Vin * (R1+R2)


                
----------


                  
R1

        
= Vin * (1 +  R2/R1)

which seems to be the acquire for a op-amp non-inverting amplifier.

The following factor to acknowledge is that the voltage throughout R1 is Vin.

In spite of everything,  Vout = Vin/H  and VR1 = Vout * H,
in order that VR1 = Vin/H * H = Vin  .

Due to this fact, the present by means of R1 is simply Vin/R  .

Assuming that the enter currents to the op-am are negligible (which
is often a very good guess) the present by means of R2 is similar as the present
by means of R1. There is no different place for it to go.

This implies we will use Vin to regulate the present by means of R2. After all,
that assumes the op-amp can provide the mandatory present and voltage.

The deflection amplifiers used within the XY displays utilized in Star Wars
provide about 2 Amps for full deflection. (The deflection amplifiers are
not TL082s.)

What if R2 is just not a resistor in any respect, however, for instance, an inductor such
as proven in Determine 18?

(The deflection windings have an inner resistance which isn’t proven.
The Vertical windings have an inner resistance of 1.1 Ohms whereas the
Horizontal windings have a resistance of 1.9 Ohms, which might be as a result of
the windings are concentric and the Horizontal windings are on the surface.
Each Horizontal and Vertical deflection windings have an inductance of
about 1 mH.)


The present by means of L continues to be the identical as the present by means of R1. The
solely distinction is that the present by means of L is frequency dependent. In
the time area an inductance resists having its present modified. The op-amp
supplies persuasion by giving it a very good swift voltage kick.

Determine 19 exhibits the voltage throughout the sense resistor (high hint) and
voltage to the deflection yoke coil (backside hint). We’re on the X axis
with a monitor take a look at display screen (not proven) that attracts a field all the best way round
the display screen. (It is from the BIP take a look at.)

1. The vector begins out being drawn to the correct. The op-amp kicks
it to get it going. As soon as it will get going it wants little or no further
voltage to develop the present ramp within the yoke.

2. When the vector stays in a single place (as a result of the Y axis is being ramped)
the X axis op-amp requires a lot much less voltage to take care of the yoke present.

3. When the vector is being drawn to the left, the op-amp offers it a
detrimental kick to get it going. As soon as it begins going it wants little or no
further voltage to develop the present ramp within the yoke.



Determine 19 – Amplifone

Voltage throughout the present sense resistor

+2.5 Volts to -2.5 Volts

Output of Deflection Amplifier

+20 Volts to -20 Volts


And, lastly, a phrase concerning the present sense resistor. It’s important
that this resistor be non-inductive. In any other case, the deflection sensitivity
will change with frequency. For a bunch of vectors of random size the
consequence will probably be unpredictable, though brief vectors will in all probability be shorter
than they need to be and lengthy vectors will probably be too lengthy.   This
sort of drawback we do not want.

For the reason that present sense resistor must dissipate extra energy than
a carbon resistor can deal with we’re left with a wirewound resistor. A normal
wirewound resistor is simply an acceptable size of resistance wire wound
round a core. See Determine 20a. This matches the definition of an inductor.

In a non-inductive wirewound resistor, there are two windings wound
on the core in reverse instructions and linked in parallel. The magnetic
fields produced by the coils cancel and thus the inductances cancel. See
Determine 20b.  (After all, even a straight wire has some inductance.) 
A non-inductive resistor has about 1% of the inductance of a normal wound
resistor of the identical dimension.

And, additional, as a result of the windings are linked in parallel, it is okay
for every section to be linked in parallel so it’s not essential to
use insulated wire.

 

 


The Amplifone Deflection Amplifiers additionally comprise a circuit that appears
at exercise on the X and Y inputs. If  it does not discover what it feels
is an acceptable quantity of exercise it turns off the Beam to stop it
from burning up the display screen phosphor. That is the notorious Spot Killer.

Even with the Spot Killer, display screen phosphor burn was a typical incidence
throughout software program improvement. One time I noticed a runaway Vector Generator
burn off the phosphor in the midst of the display screen, then burn fully
by means of the shadow masks, and begin to burn by means of the glass.

Here are the full schematics for the Amplifone
XY Monitors, followed by the schematics for the Wells-Gardner XY Monitor
.





Excessive Voltage Energy Provides


By now everybody has heard the story of the Universally-Hated Atari Govt
who went all the way down to Brownsville to go to Amplifone, ignored requests to not
smoke contained in the constructing, and triggered the hearth sprinklers, ruining each
Amplifone HV transformer ever made. Whereas there was by no means any scarcity
of Universally-Hated Atari Executives, and whereas an incident of this kind
may have occurred, I’ve my doubts about it. For one, I did not hear
about it till I noticed it on the Net about two years in the past, lengthy after I left
Atari Video games.

The story I heard, whereas I used to be nonetheless at Atari, was that the strategy used
to make the HV transformers turned out to be delicate to humidity, and
the primary HV transformers to deplete had been those made throughout hurricane
season.

Very probably, the true story is just that the potting materials used
within the transformers was lower than the duty.

Whatever the trigger, by the point the issue appeared the Operators
had already made a very good return on their funding. That was excellent news
for the Operators however unhealthy information for these of us attempting to maintain their 17
year-old Star Wars video games alive.

I’ve had two Amplifone HV transformers deplete in my TomCat sport. I
lastly changed the HV meeting with one from a Wells-Gardner monitor.
The one distinction is that the Wells-Gardner provide doesn’t present 6.3VAC
for the CRT heater. (I put in a 6.3VAC filament transformer.)

The HV provide in my Star Wars sport nonetheless works fantastic, though the sport
doesn’t have all that a lot flight time logged.

For the report, I used to be the Mission Engineer on Star Wars, however I did not
design the monitor. (I actually did not design the Excessive Voltage Transformer.)

Let’s begin initially.

When televisions had been first made within the late Nineteen Forties the excessive voltage
energy provides used transformers that operated from the road at 60 Hz.
I do know, as a result of I had one. (My father knew the proprietor of the TV restore store
on the town and I might periodically get junk TVs to take aside. Folks left
them as a result of they determined they weren’t price fixing/adjusting. Some had been
left as a result of they had been simply previous.)

Screens had been small (a ten inch display screen was widespread) so the excessive voltage
was in all probability solely 10 KV. The issue was that filtering the 60 Hz output
required a big excessive voltage (10 KV) capacitor. One of many causes that
60Hz was chosen because the vertical sync price was in order that 60 Hz hum wouldn’t
be as noticeable. Finally, somebody acquired the thought to make use of the horizontal
frequency (15,750 Hz) to supply the excessive voltage utilizing a flyback transformer.
Working on the greater frequency meant you can use a decrease worth capacitor.

 


The usual excessive voltage capacitor was 500 pF.  It was known as a doorknob
capacitor
as a result of that is what it appears like. That is what a contemporary
doorknob capacitor appears like.    >>>>>>

Connections are made with screw terminals on the highest and backside. The
previous TV doorknob capacitors had been often beige/orange and had ridges round
the cylinder.

These days they coat each the within and outdoors of the CRT envelope with
a conductive materials, forming a capacitor. The within coating connects
to the HV connector and the surface coating is grounded. The capacitance
finally ends up being about 2000 pF. (Do not “clear” it off.)

The best way a flyback transformer works is that you just cost it with present
(comparatively slowly) after which launch it unexpectedly. That is as a result of, in
an inductor, the voltage developed throughout it’s proportional to the speed
of change of the present:

    V = L * di/dt

The flyback transformer is charged through the energetic horizontal time
(50 us) and discharged as a Huge Zap throughout Horizontal Sync (about 8 us). 
(Whenever you add back and front porch blanking you find yourself with 63.5 us, which
is the horizontal interval.)

An extra function is that the charging of the inductor additionally supplies
the present ramp for the horizontal deflection coils.

The voltage nonetheless must be stepped up, so there’s a secondary winding.
The output of the secondary winding is then rectified by a diode that’s
often encapsulated contained in the flyback transformer and filtered by the
capacitor that’s constructed into the CRT.

See Also

The Huge Zap happens throughout Horizontal Blanking. Any sagging of the HV
additionally happens on the horizontal price and isn’t as noticeable as if it occurred
randomly throughout energetic video.

The issue with XY is that there isn’t a Horizontal Sync, so the Huge
Zap happens randomly within the vectors. Truly, the Huge Zap happens at common
intervals, it is from the vectors’ perspective that it happens randomly.

The standard knowledge is that the HV Provide for an XY Monitor should
generate a sine wave to keep away from this drawback The handbook for the Electrohome
B/W XY Monitor explicitly mentions that it makes use of a sine wave circuit.

I heard of a Collector who tried a tv HV Provide in his Star
Wars. Based on somebody who noticed it, it exhibited noticeable (and ugly)
Vector Beating. It appeared that the one approach to repair a burned-up Amplifone
HV transformer was to purchase an costly alternative from Wintron.

Now I am not so positive.

Within the technique of placing this text collectively I put an oscilloscope
on the Wells-Gardner HV Provide in my TomCat. Since I haven’t got a particular
(and costly) excessive voltage probe, I appeared on the collector of Q906,
the transistor that drives the HV transformer. (The schematics for the
Wells-Gardner HV Provide are within the earlier part.)

What I acquired is proven in Determine 21. It does not seem like a sine wave to
me.


Determine 21 – Wells-Gardner Coloration XY Excessive Voltage Provide Waveform
at Q906 Collector

Voltage = -24VDC to +250VDC

Time Between Pulses = 52 us.

Pulse Charge 19.2 KHz.

 

The truth that there’s 250V wherever on a major winding in a circuit
powered by 48V (-24V and +24V) is a useless giveaway that it’s working
in flyback mode.

In addition to, even with a sine wave, while you rectify it and use a capacitive-input
filter, you get a Huge Zap.

I carried out an additional experiment utilizing a Philips Mono VGA Monitor (mannequin
7BM749CH01). This can be a B/W monitor that mixes the RGB indicators and runs
at VGA Sync frequencies.

I linked the HV output (in all probability 15 KV) to the anode of the CRT in
my TomCat. The monitor began life as a inventory Amplifone monitor so the
CRT might be a 19VJTP22.  I left every thing else (Heater, G2, and
Focus) linked to the Effectively-Gardner provide.

There was simply sufficient vary within the Focus management to regulate to the decrease
anode voltage.

Sadly, the outcomes weren’t definitive.

1. The display screen was noticeably dimmer, as you’d anticipate with a decrease
anode voltage. (Growing the G2 voltage made it not possible to focus the
beam.)

2. There was some Vector Beating within the sport, but when I hadn’t been wanting
for it, I would not have observed it (at the least not instantly). It did not
intrude with the sport.

3. Vector Beating was extra evident within the take a look at patterns, particularly
the Cross Hatch sample. The Philips provide was working at round 16
KHz. Growing the frequency had some impact on the beat sample, suggesting
there was an interplay between the HV from the Philips provide and the
G2 (and focus) from the Wells provide. I think that working all of the
CRT voltages from the identical provide would cut back vector beating and that
working at a better frequency (like 32 KHz) would give higher outcomes.
(After I elevated the frequency of the Philips provide the HV decreased,
making it not possible to focus the beam.)

This implies that the HV provide from an previous pc shade monitor
(with a schematic) may be used to energy shade XY displays. The necessities
are:

1. Both the Excessive Voltage provide have to be remoted from the
energy line or an isolation transformer have to be used.

2. Both the circuitry that shuts down the monitor within the absence of
sync have to be disabled or a easy sync generator have to be constructed (two
555s producing 32 KHz and 60Hz respectively).

3. Any electrical pincushion correction should even be disabled. Since
the Horizontal Deflection coils are intimately concerned within the excessive voltage
circuit, any modulation of the Horizontal coils will in all probability additionally modulate
the Excessive Voltage.  (I ponder if the issue when the Collector
used a tv Excessive Voltage provide in his Star Wars was as a result of presence
of a pincushion correction circuit. Somebody with a excessive voltage probe and
a spectrum analyzer is invited to analyze this facet additional.)


If vital, the outputs (anode, focus, and G2) might be filtered by including
capacitors or by altering to an inductive-input filter.  (The filtered
voltage could be much less, however may be sufficient.)

 

A last phrase on Excessive Voltage Provides.

When an electron beam is accelerated at a goal at energies above 25KV
it begins to supply ionizing radiation, generally often called x-rays.

Within the Nineteen Sixties, as gross sales of shade TVs took off, producers began
utilizing excessive voltages as excessive as 30KV – 35KV in an effort to produce brighter
footage. Both the producers did not know they had been producing x-rays
or they did not care. Maybe they determined that the quantity of x-rays was
small in comparison with the dose everybody was already receiving from nuclear
fallout produced by the atmospheric testing of nuclear bombs. (And within the
Nineteen Fifties, shoe shops had x-ray machines to let you look down and see
how nicely your sneakers match.)

Folks (particularly dad and mom) had been involved, and the Authorities lastly
did one thing about it. At present, TVs should not permitted to supply excessive voltages
in extra of 25 KV, and safety circuitry is required in order that failure
of a single element (or any single-point failure) is not going to enable the
voltage to rise above 25 KV.

 

Now a particular deal with for Amplifone junkies.

I used to be current on the first assembly Atari had with Amplifone. It took
place once we had been in Sunnyvale at 1272 Borregas. The very first thing Ted Handing
(Jr.) did was give every of us a pocket book crammed with details about
Amplifone. (Mine was numbered 0053).  I keep in mind Ted as an enormous, pleasant
man who sort of jogged my memory of Hoss Cartright. (If you do not know who Hoss
Cartright was, ask your dad and mom.)

Effectively, I stored the pocket book and have scanned it. Right here is the first
page (310 KB – PDF)
.

You’ll be able to obtain the whole notebook right here.
Warning, it’s 9.2 MB (PDF). (I’ll preserve it obtainable till I want the
server house for one thing else.)





Display Phosphors


We now have an Electron Gun producing an Electron Beam, accelerated
by the Excessive Voltage on the Anode, and with the power to maneuver the Electron
Beam round through the use of the Deflection Amplifiers to regulate the present in
the Deflection Coils.

Since we can not see the Electron Beam immediately, the face of the CRT
is coated with a Phosphor which absorbs the power of the electrons and
re-emits it as seen gentle. This course of is named cathodoluminescence.

Phosphors are usually gentle metals similar to zinc and cadmium 
within the type of sulfide, sulfate, and phosphate compounds which are processed
to supply very fantastic particles that are deposited on the display screen.

A skinny (100 to 300 nm) metallic layer (often aluminum) is then deposited
over the phosphor coating with the next advantages:

1. The reflecting aluminum floor displays the sunshine that may in any other case
go to the again of the CRT, thereby doubling the quantity of sunshine that comes
out the entrance.

2. It prevents the phosphor from being charged by the electron beam.
Earlier than the strategy of aluminizing the phosphor was developed, the phosphors
needed to be formulated to facilitate the secondary emission of electrons,
which compromised the phosphors’ efficiency.

3. It protects the phosphor from being broken by ion-bombardment.

Ion-bombardment has an fascinating historical past. We are going to begin with two questions.

1. Why are there ions in my CRT?   Ions are current from a
mixture of getting an imperfect vacuum and from outgassing of the supplies
used within the CRT.

2. Why are ions an issue?   Damaging ions (being detrimental)
are accelerated towards the display screen identical to electrons. Nevertheless, as a result of
ions are a lot heavier they do not get deflected very a lot (if in any respect).
Because of this, all of them find yourself within the heart of the display screen the place they trigger
the phosphor to deteriorate. Usually (at the least in a B/W CRT) it causes
the phosphor to show brown. That is very noticeable, sort of like a phosphor
burn.

When TV units had been first supplied on the market (on the 1939 World’s Truthful)
they ranged from $200 to $600, which represented a number of months of a median
employee’s wage.  Display sizes ranged from 5-inches to 12-inches and
as a result of the expertise at the moment didn’t allow vast deflection angles,
the images tubes had been lengthy. So lengthy, in actual fact, that within the larger-sized
fashions the units had been mounted vertically. A hinge-mounted mirror on the
high of the receiver cupboard permitted viewing. Having the CRT of their
costly TV develop an ion spot would have pissed folks off.  (Word:
the event of tv was interrupted by the Second World Struggle and
didn’t actually begin till the Struggle was over.)

The primary resolution to the issue was to mount the electron gun crooked,
in order that it was aimed on the neck as an alternative of the display screen. For the reason that CRT neck
was comparatively lengthy, this didn’t require a lot of an angle. A magnet mounted
on a hoop across the neck straightened out the electron beam. The ions,
being a lot heavier, don’t get deflected and proceed on to hit the neck
the place they’ll do no hurt. The magnet that does that is known as the ion-trap,
and was yet another factor that was enjoyable to play with.

Aluminized phosphor screens had been developed within the late Nineteen Forties, however there
had been many TVs manufactured within the Nineteen Fifties that continued to make use of ion-traps
and previous phosphors.

A last phrase on the aluminized layer. Though it’s electrically conducting,
it’s skinny sufficient that it doesn’t intrude with the electron beam thrilling
the phosphor.

There are a number of essential traits of phosphors.

One is the colour (clearly).

The property of sunshine emission throughout phosphor excitation is named
flourescence. The property of emission instantly after excitation is
known as phosphorescence. For many phosphors, the colour emitted by flourescence
and phosphoresence are the identical. Nevertheless, there are some for which this
is just not the case.

One other essential attribute is persistence, which is the time it
takes for gentle emitted from the display screen to decay to 10% of its most
worth.

A protracted persistence time is used when the display screen replace price is sluggish,
similar to within the Deliberate Place Indicator (PPI) utilized in previous radar shows.
After all, in case you replace it often, it smears.

The persistence time for the phosphors utilized in CRTs supposed for video
is characterised as Medium-Quick.

There’s a record of ordinary phosphor sorts going from P1 – P41. 
Just a few are utilized in customary merchandise, similar to P22 (R,G,B Coloration) used
in shade tv and video and P4 (White) utilized in B/W televisions. P1
(Yellow-Inexperienced) is (or was) widespread in oscilloscopes; the Tektronix 465 used
P31 (Inexperienced) with P11 (Blue) as an choice.

A P7 phosphor is Blue in flourescence (when the beam is hitting it)
and Yellow in phosphorescence (after the beam stops). The 2 colours additionally
have completely different persistence instances. Blue is Medium-Quick whereas Yellow is
Lengthy.  That is in all probability why it was utilized in radar.

Particular goal lengthy phosphors like P7 are in all probability out of date because it
is now simpler to make use of a normal raster show and simulate the required
results in software program. In 1999 Tektronix ran a sequence of advertisements saying they
had invented one thing they known as  “Digital Persistence” which was
a technique for simulating the decay traits of an analog CRT on a
digital system. It seems they had been a bit late to the social gathering. Atari developed
the strategy for the radar show in Subs (launched in 1977).

The next is record of the usual phosphors. It comes principally from
Whitaker; nevertheless, I’ve corrected the errors he made in defining persistence
instances. (The entire microseconds had been mislabeled as milliseconds.)

Phosphor Listing (from Whitaker)


          Coloration*    
Persistence**   Supposed Use



    Fluorescent 
Phosphorescent


P1      YG     
YG        M          
Oscillography, radar


P2      YG     
YG        M          
Oscillography


P3      YO     
YO        M


P4      W      
W         MS         
Direct view tv


P5      B      
B         MS         
Photographic


P6      W      
W         S


P7      B      
Y         MS(B),L(Y)  Radar


P8    changed by P7

P9    not registered

P10   darkish hint display screen   VL         
Radar


P11     B      
B         MS         
photographic


P12     O      
O         L          
Radar


P13     RO      RO       
M           Radar


P14     B      
YO        MS(B),M(YO) Radar


P15     UV      G        
UV(VS),G(S) Flying-spot scanner


P16     UV      UV       
VS          Flying-spot scanner,photographic


P17     B      
Y         S(B), L(Y)  Oscillography,
radar


P18     W      
W         M-MS       
Projection tv


P19     O      
O         L          
Radar


P20    YG       YG       
M-MS        Storage tube


P21    RO       RO       
M           Radar


P22   (R,G,B)  (R,G,B)    MS         
Tricolor video (tv)


P23    W       
W         MS         
Direct-view tv


P24    G       
G         S          
Flying Spot Scanner


P25    O       
O         M          
Radar


P26    O       
O         VL         
Radar


P27    RO       RO       
M           Coloration TV
monitor


P28    YG       YG       
L           Radar


P29    P2 and P25 stripes            
Radar, indicators


P30    Cancelled

P31    G       
G         MS         
Oscillography, shiny video


P32    PB       YG       
L           Radar


P33    O       
O         VL         
Radar


P34    BG       YG       
VL          Radar, oscillography


P35    G       
B         MS         
Oscillography


P36    YG       YG       
VS          Flying-spot scanner


P37    B       
B         VS         
Flying-spot scanner, photographic


P38    O       
O         VL         
Radar


P39    YG       YG       
L           Radar


P40    B       
YG        MS(B),L(YG) Low repetition
price (Pl 2 and Pl 6)


P41    UV       O        
VS(UV),L(O) Radar with gentle set off

* Coloration: B = blue, 
P = purple,  G = inexperienced,  O orange, Y = yellow,  R purple, W
white, UV = ultraviolet

** Persistence to 10%
decay stage:


      
VS (Very Quick) = lower than 1 us


      
S  (Quick) = 1 us to 10 us


     
MS (Medium-Quick) = 10 us to 1 ms


     
M (Medium) = 1 ms to 100 ms


     
L  (Lengthy) = 100ms to 1s






Coloration CRTs


If this can be a monochrome (B/W) CRT we’re finished.

However a shade CRT makes use of three phosphors and a technique for thrilling every
one individually. There are two alternative ways of arranging the phosphors.

Within the Delta technique there are triads of three dots organized in a delta
configuration, as proven in Determine 22a. Three are additionally three electron beams
organized in a delta configuration. Immediately in entrance of the phosphor display screen
is the shadow masks, with a single gap in entrance of every phosphor triad.
The geometry is such that the Crimson electron beam solely sees the Crimson phosphor
dot. The Shadow Masks shades the Inexperienced and Blue dots within the triad from the
Crimson electron beam. Equally, the Inexperienced electron beam solely sees the Inexperienced
phosphor dot and the Blue electron beam solely sees the Blue phosphor dot.
See Determine 22b. (After all, this assumes that every thing is completely converged.)

The benefit of the Delta Gun is that it permits the phosphor dots to
be positioned shut collectively (smaller pitch). The associated fee is that convergence
is tougher as a result of the electron beams should not in the identical airplane
and are subsequently affected barely in another way by the magnetic fields
used to maneuver them round. Convergence can also be extra demanding as a result of it
does not go away a lot room for error.

 

Within the second technique, known as the In-Line technique, the phosphors are organized
in triads of three phosphor stripes as proven in Determine 23a. The electron
beams are organized side-by-side and the shadow masks has a slot in entrance
of every phosphor triad. See Determine 23b.

Whereas the In-Line Gun produces a bigger pitch, having the electron beams
in the identical airplane makes them extra uniformly affected by magnetic fields.
The slot additionally leaves permits extra room for error.

There’s a good purpose why the slots are vertical as an alternative of horizontal.
I noticed this at some point after I was evaluating the colour purity of a monitor.
The monitor was on a wheeled cart and was oriented with the display screen vertical
however with the lengthy facet up, like in Centipede. I had a pure purple display screen displayed. 
For some purpose it was vital to maneuver the cart, and within the course of it
acquired turned 90 levels. Impulsively I used to be taking a look at a pure blue display screen.
I believed to myself, “what is the deal?” (I wasn’t operating Home windows.) I turned
the monitor again to its unique place. It was purple once more. I appeared round
to see if this was the work of some prankster however I used to be the one one there.
I turned the cart a number of instances and at all times acquired the identical consequence. That is
after I realized what was happening.

Except you’re situated within the excessive Northern or Southern latitudes,
the Earth’s magnetic area is principally horizontal. Keep in mind that a horizontal
magnetic area deflects an electron beam vertically.  That implies that
when a monitor is oriented usually, the Earth’s magnetic area strikes the
electron beams throughout the vertical slots so it does not screw up monitor
purity. Because of this, degaussing is just not as vital.

If the monitor is mounted ala Centipede, you lose that benefit.





Options

Various #1 – Use A/Ds (in all probability at the least 20 MHz) on X, Y, R, G,
B, stuff the information right into a body buffer, and show it on a raster monitor.

{Hardware}:

A/Ds: 10-bit A/Ds on X and Y, 8-bit A/Ds on R, G, and B

Body Buffer: two buffers of 1024*768*24 bits = 4,718,592 bytes.

To keep away from awkward line boundaries, use two buffers of 1024*1024*24 bits
= 6,291,456 bytes = ~ 6 MBytes

Management:  FPGA for reminiscence management and video sync, possibly DSP for
body price conversion


{Hardware} Points:

These days, a lot of the fascinating elements appear to be Floor Mount
Gadgets (SMDs). SMDs are usually tough (or not possible) to prototype,
require multilayer PCBs (at the least 4 layers), and the PCBs require a
solder masks. PCBs of this kind are costly, particularly in prototype portions.
The specialised tools for soldering SMDs can also be costly.

Software program points:

If the raster refresh price is completely different from the vector refresh price
the display screen information is not going to be correctly displayed.

The display screen refresh price for Star Wars is about 24 ms (42 Hz). That guidelines
out customary NTSC displays. It is also too sluggish for Laptop displays. Nevertheless,
pc displays could possibly run at twice that price (84 Hz). Interpolating
between frames is feasible to carry out scan conversion, however requires appreciable
processing and by no means appears all that good anyway.

There may be additionally the latency drawback. Digitizing the sign would require
that you just fill a buffer earlier than you show it. That implies that the image
you see will probably be at the least one refresh body behind, which will probably be at the least
12 ms. The latency time in an interactive system is vital, and even
a 12 ms delay will probably be sufficient to make the controls seem sluggish.

I am not saying this technique is not possible, simply that it might be very
tough.

_____________________________________________________________________________________

Alternate #2 – Use a Flat Panel Show, which is inherently XY Addressable.

Though Flat Panel Shows similar to LCDs, Plasma Shows, and Area
Emission Shows (FEDs) are inherently XY addressable, the motive force ICs
are usually built-in on the panel, making it tough to switch.

That is a disgrace, because the panel interface would solely want an X Register,
a Y Register, and three shade registers. (The digital indicators would come
from A/Ds.)

For the reason that pixels could be written in actual time with no buffer, there
could be no added latency.

 

Various #3 – For  the Future

There may be appreciable work being finished on Natural Semiconductors, particularly
Natural LEDs, particularly to make Flat Panel Shows. Consider Natural
Semiconductors as Plastic. One large benefit is that the processing is
finished at a lot decrease temperature than that used to make conventional semiconductors.
They’re speaking about utilizing a producing approach just like peculiar
printing. That is anticipated to convey the price of Flat Panel Shows method
down.

If the method turns into very low-cost it might be doable to have prototypes
made for an inexpensive value. After all, our prototypes could have the X,Y,R,G,B
inputs we want.

Maybe, at some point, we can purchase our personal cheap printers
and make our personal panels, in addition to processors and reminiscence.



References


Video Show Engineering by Jerry Whitaker, McGraw-Hill, 2001.
{If you wish to be taught extra about this topic that is the one to purchase, even
although it prices $80. Additionally they have a Website online at www.tvhandbook.com }

Primary Tv Ideas and Servicing by Bernard Grob, McGraw-Hill,
1975.

Digital Parts Handbook by Thomas H. Jones, Reston Publishing
Firm, 1979.

Fundamentals of Show Techniques Design by Sol Sherr, Wiley Interscience,
1970

{ After I purchased this guide within the Eighties I paid $35.50 for it. A second
version was printed in 1993 and prices $180.00 on amazon.com .  I
do not suppose I will purchase it.}

Ideas of Electron Tubes by Herbert J. Reich, initially
printed in 1941. Reprinted by Audio Newbie Press 1995. { This can be a nice
guide in case you are keen on vacuum tubes.}

________________________________________________________________________________________

Copyright 2001 Jed Margolin







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