Re: New vector monitor design.

At 05:31 PM 5/23/97 EDT, you wrote:
>Forgive me if this subject has been beaten to death here previously.
>
>Besides, we need something to do while the hackers are finishing
>the Zektor mods :)
>
>Whilst digging through some trashed out monitors, I noticed that
>the horizontal yoke deflection coils from some monitors can be
>removed without too much hassle.
>
>Since the vertical response seems to be the limiting factor in some
>experiments by Clay and company, would somebody who knows more
>about monitor design care to comment on the feasability of the
>following.
>
>Take one monitor yoke, remove horizontal windings. Take another monitor
>yoke of the same type, disconnect the vertical windings and attach other
>horizontal windings. Orient loose horizontal winding 90 degrees from
>other
>horiztontal windings. Place & align new yoke on a WG K6100 compatible
>tube. Attach K6100 chassis to tube. Turn on & watch for smoke :)
>
>Would this even work? Since the horizontal winding is 15.750 KHz, would
>there be any response outside of a small window around 15K?
>
>Any comments from the monitor wizards? Gregg? Zonn? Ferris? Anybody?

One of my "too do" projects is a 27"+ X/Y monitor (depends on how much money
I could spare, I'd really like a 32"!).

The way to do this is to convert one of those new 32 inch TVs.

Of all the problems, the Yoke seems to be the hardest.

By running the TV with a blank screen (or blue, or whatever) I can allow the
TV to generate it's own High Voltage, Focus Voltage, and I can tap into it's
anode voltages to drive the RGB guns.

That leaves the yoke. The easiest thing to do would be use an WG / Sega or
Amplifone yoke, that's if they will even fit over the end of the tube.

The problem with this is the yoke was not designed for the tube, and chances
are converging the tube will be impossible.

So the next thing would be to use the raster Yoke supplied with the tube.
The advantages are that if you don't move it around, it'll probably be
pretty close to converged.

The disadvantages are of course the high impedances.

The TRUE monitor guru is Rodger Boots (I don't think he's on this mailing
list). Rodger works on military monitors for a living, and has even worked
on dual raster / X-Y monitors. They're used in aircraft radar, they scan
one frame of raster for background, then switch to an X/Y mode to display
the radar images. Flipping back and forth between the two modes allows for
killer overlays on an X/Y display -- anybody have one of *these* laying
around in their garage?

So after sending a few emails off to Rodger I found out that of the four
coils used in any yoke (2 vertical, 2 horizontal), X/Y monitors have these
coils connected in parallel, for lower impedances, while rasters have the
horizontal coils in parallel and the vertical in series (for higher impedances).

So far, every raster yoke I've looked would allow me access to the windings
where I could re-connect the vertical windings in parallel, instead of series.

The tuning of the yoke for 15khz is done with an external capacitor, which
would be removed. (The clicking you hear in many multi-scan monitors as you
change video modes, are relays switching in and out different capacitors to
tune the monitor's yoke for different scan rates.)

Of course this still doesn't create the ideal X/Y yoke, the impedances are
still much higher than the standard X/Y yoke.

So step #2, there's nothing in physics that says high impedance yokes can't
be driven just as fast as the low impedance yokes, you just need higher
driving voltages. I'm guessing for a rewired raster yoke, something on the
order of +/- 100 volts. (Using standard raster isolation transformers and
some surplus capacitors I should be able to build the +/- 100v power supply)

Well it's hard to find high voltage / high current bipolar transistor, and
as a side note Rodger mentioned high power Mos-FETs which have much higher
break down voltages.

For driving the yokes I planned on using an old amplifone X/Y board since
the flybacks are fried in all the Amplifone boards I have, they're
available. And they have a nice, everything on one board but the high
voltage, layout.

So now I need to beef up the outputs to handle +/- 100v (at least) levels.
Looking into Mos-FETs the first thing you find is that they are voltage
amplifiers, not current amplifiers (like standard bi-polar transistors).
This is actually an advantage since I can now drive the Amplifone circuitry
with the standard +/- 25v levels, use a properly calculated resistor to
convert the currents from the pre-drivers to the proper voltages needed to
drive the Mos-FETs, and use the Mos-FETs to do the voltage amplification to
+/- 100 volts.

The other thing nice about Mos-FETs is that they *like* being paralleled as
drivers. When they get hotter, they conduct *less* current, so are self
regulating (they don't need those emitter resistors -- well they don't
actually have emitters).

After all that's done, there will probably be problems with pincushioning
and such, since the newer tubes have flatter screens, and shorter yoke
distances. (this is of course assuming I can even get the tube to converge!)
I'm sure to compensate for these anomalies, some clever circuitry has been
added to the TV, to square up the edges. The Cinematronics color card has
some nice, completely adjustable, pincushion correction, and also circuits
to adjust linearity without those impossible to find VDR's. I'll use
something like these circuits to play with squaring up the edges.

So in summary:

Find a big TV, with schematic.

Either work with available X/Y yokes (by far the *easiest* if it works!)
  else, rewire raster yoke and redesign the X/Y power amplifiers.

Verify anode voltage levels are acceptable to Amplifone (or patch up this
circuit)

Add whatever pincushion and linearity correction circuitry I might need.

Hook up to Tempest or Star Wars for the totally killer big screen effect!

(Or how about a 32" 4 player eliminator screen! Cool! Geeze maybe I need
+/- 150 volts to run Sega stuff! *gulp*)

So as long as I don't do something stupid like brush up against the 250
volts, plus, power supply, while I'm building this thing, it looks like a
peice of cake! (Children please don't try this at home!)

-------------------

Well that answer had nothing to do with your original question!

So to answer your question about whether using to horizontal raster coils
wired at a 90 degree angles to each other, as an X/Y yoke:

I don't know.

Because of the higher impedances of the yoke I would think the monitor would
be too slow, you'd have to boost the power supply voltages, assuming you
could get the monitor to converge.

-Zonn
Received on Fri May 23 16:14:21 1997