Quasi-interesting CRT puzzler

[Helmut Sennewald]

Yipes! Luckily I overstated the actual situation-- we only need to
draw about 20 full-screen lines 60 times a second, so we only need 10
amps at 1/5th of that, or 60 volts I think. In addition we need to
draw up to 100 1/4 inch high characters at 60Hz, so applying the fudge
factors, hmmmm.... 60 volts may be plenty. Well within the capability
of a HV op amp with a couple booster transistors. And a heat sink And
a fan.

Crazy project

Hello,

Maybe you should look for a very small monitor. They require
less current because of their smaller tube.

Best regards,
Helmut

 

[Ancient_Hacker]

Thanks everyone for all the good suggestions and links.

If I can't get the power amps and Z-axis stuff to work, there's a
building full of old arcade machines for sale down the pike. Not to
mention the occasional CAD/CAM vector monitor on eBay once in a while.

 

[Mark]

Thanks everyone for all the good suggestions and links.

If I can't get the power amps and Z-axis stuff to work, there's a
building full of old arcade machines for sale down the pike. Not to
mention the occasional CAD/CAM vector monitor on eBay once in a while.

Why don't they use ELECTROSTATIC defelction?

Mark

 

[Graham Holloway]

Why don't they use ELECTROSTATIC defelction?

Mark

Because the CRT is generally small, very long and dim.

Graham H

 

[Nico Coesel]

Yipes! Luckily I overstated the actual situation-- we only need to
draw about 20 full-screen lines 60 times a second, so we only need 10
amps at 1/5th of that, or 60 volts I think. In addition we need to
draw up to 100 1/4 inch high characters at 60Hz, so applying the fudge
factors, hmmmm.... 60 volts may be plenty. Well within the capability
of a HV op amp with a couple booster transistors. And a heat sink And
a fan.

How about a class-D amplifier? Besides, 60 screen updates per second
is not enough for a computer monitor. You'll need at least 70Hz.

 

[John Woodgate]

Why don't they use ELECTROSTATIC defelction?

There aren't any ESD tubes made. Chicken and egg.

 

[Ancient_Hacker]

There aren't any ESD tubes made. Chicken and egg.
--

HP must have had some made up, long ago, for their 13xx series of
monitors.

But in general electrostatic deflection isnt popular in the larger
screen sizes, as the tube gets too long-- apparently it's hard to get
much of a deflection angle electrostatically without defocusing the
spot too much.

 

[John Woodgate]

HP must have had some made up, long ago, for their 13xx series of
monitors.

But in general electrostatic deflection isnt popular in the larger
screen sizes, as the tube gets too long-- apparently it's hard to get
much of a deflection angle electrostatically without defocusing the
spot too much.

That can be fixed. But the resulting tube is complex and costly.

 

[YD]

Okay, this is kind of a retarded question, but here goes.

Let's say you want to convert you basic PC monitor from raster scan to
vector.

You pull off the yoke connector from the main board and find out the it
still runs okay, well except that you've burnt a little spot of
phosphor in the center of the screen unless you were prescient enough
to back off the brightness, contrast, and the three screen controls
first.

Then you hook up a DC supply to the V and H yoke coils and find out it
takes about 3 AMPS to do a full screen deflection in the vertical
direction, about TEN amps in the horizontal direction.

(I think that's because the horizontal deflection has to happen faster,
therfore lower inductance in the h coil, therefore fewer gausses per
amp).

So we need some pretty hefty drivers, many amps plus many volts if we
want fast deflection.

Not a huge problem so far.

But now we realize we don't want to burn the screen if we're drawing
short or slow vectors, and we don't want the lines to be invisible if
we're drawing them long or quickly.

So we need some sort of Z-axis brightness modulation, somehow
proportional to the "writing rate", like in inches per millisecond or
thereabouts.

Anybody have any idea how to compute this on the fly as it were?

Ideally I'd like to be able to draw 6000 full length vectors per
second.

A quick web search didnt find anything promising.


Regards,

George

Can't be arsed to look through the whole thread to see if someone else
has come up with this. Just a WAG anyway. Since fast vectors mean a
high di/dt and consequently slow vectors a proportionally lower di/dt
it would seem you could use that for the Z modulation. Just find
somewhere to take it off the signal path before the coil drivers. Of
course, you'll need to use the abs() value.

- YD.

 

[YD]

Yipes! Luckily I overstated the actual situation-- we only need to
draw about 20 full-screen lines 60 times a second, so we only need 10
amps at 1/5th of that, or 60 volts I think. In addition we need to
draw up to 100 1/4 inch high characters at 60Hz, so applying the fudge
factors, hmmmm.... 60 volts may be plenty. Well within the capability
of a HV op amp with a couple booster transistors. And a heat sink And
a fan.

Crazy project!

Ouch, 3 kW peaks. Ok, average may be a lot less but better use it only
on cold nights. Have you tried to find out how the Asteroids game does
it? Must be something a lot more efficient.

- YD.

 

[Rich Grise]

Yipes! Luckily I overstated the actual situation-- we only need to
draw about 20 full-screen lines 60 times a second, so we only need 10
amps at 1/5th of that, or 60 volts I think. In addition we need to
draw up to 100 1/4 inch high characters at 60Hz, so applying the fudge
factors, hmmmm.... 60 volts may be plenty. Well within the capability
of a HV op amp with a couple booster transistors. And a heat sink And
a fan.

Crazy project!

Yeah. So, if you're going to do that, then take the yoke off and cut the
windings off it. But keep the form, of course. Following the winding
pattern of the old coils, wind about 20-30 turns of #18 or so for each
coil, symmetrically, and slap it on the tube, pass a couple amps through
it, and see what you get.

Oh, wait. Before you tear the yoke apart, measure the DC resistance
and inductance of the windings, and duplicate that (4 coils) and
plug them in in place of the yoke, so the Hor. osc. will work and you
get HV.

Or, just make a new form, wind as above, and plug the old yoke back in.


Good Luck!
Rich

 

[jasen]

So we need some sort of Z-axis brightness modulation, somehow
proportional to the "writing rate", like in inches per millisecond or
thereabouts.

Anybody have any idea how to compute this on the fly as it were?

rectify the X and Y rate square them. add the squares and take the root of
that. (this is pythagoras' theorem.)

if that's too hard rectify the rates,and add 1/3 of the lesser to the greater
it'll be almost right. (+/- 5%)

Bye.
Jasen

 

[jasen]

Can't be arsed to look through the whole thread to see if someone else
has come up with this. Just a WAG anyway. Since fast vectors mean a
high di/dt and consequently slow vectors a proportionally lower di/dt
it would seem you could use that for the Z modulation. Just find
somewhere to take it off the signal path before the coil drivers. Of
course, you'll need to use the abs() value.

add a second winding to both x and y, feed both through bridge rectifiers
and then hook em in series.

 

[joseph2k]

Tuned deflection coils, more efficient use of power?

I worked on a radar display in the early 70's that used deflection coils
of around 10uH total. We used a class A push-pull output stage with
centre-tapped coils and a series inductor. We got around 5MHz small signal
bandwidth. The energy stored in the inductor provided the high voltage
needed for fast transitions of the beam. The system could display a 625
line TV picture and write all over it with vectors and characters in the
vertical flyback period. Problem - 800 watts per axis!

Graham H

In the Mid '70's i worked on radar consoles about 20" that could do TV
raster, normal radar scan, spiral scan, and paint a bunch of randomly
placed symbols and text. It was electrostatically deflected with 2200 V
transistorized amplifiers; three transistor totem poles each side.

 

[Kevin White]

Okay, this is kind of a retarded question, but here goes.

Regards,

George

The schematics for the Atari games are at:
http://www.cityofberwyn.com/schematics/

kevin