CurtPalme.com Home Theater Forum

[Sparky015]

Mike,
Did you ever find the glue to lock down the deflection coil? I was going to begin my search, but didn't want to re-invent the wheel if you were willing to share.

[mp20748]

No, I actually left the tabs on the convergence coils in my final setup with things.

So leave the tightening ring in place and push the focus coil all the way forward to the convergence coil.

[Sparky015]

hmmm, I'll try it again. I couldn't get the tightening ring to slide over the convergence coil tabs. I had to remove the ring from the focus coils to get them to go over the tabs. I'll play more with it tonight. My goal is to finally fire up these bad boys by the end of the week!

[mp20748]

[Sparky015]

Mike,
I'm with you there. Are you saying you didn't remove the lock ring on the convergence coil? I thought you had removed that to get the focus coil as far upward against the convergence/defection coil assembly as possible? I removed the lock ring, but the 909 focus coil with it's tightening ring installed, will not slide over the convergence coil tabs. I'll snap a picture so you see what I'm saying.

[cmjohnson]

I'd just like to point out that no matter what focus yoke you choose to use, its static magnetic strength needs to be correct for a Marquee or you'll have to roll in a lot of static focus adjustment in order to get good focus, and if you need too much static focus adjustment,
you may not have enough dynamic focus range available.

The magnetic field strength at the center axis of the coil should have a peak reading of 294 gauss, give or take maybe three points. If your coil magnet strength is significantly off from this range, you won't ever get optimal focus range values.


Additionally, the static and dynamic coils need to be very close to these ideal values:


Static winding: 30 milliHenries
Dynamic winding: 45 microHenries

Both should be wound of the largest gauge magnet wire that will allow you to get the required number of turns on the bobbins and
still fit in the alotted space, to keep DC resistance to a minimum, thus increasing the current carrying capability and hence the magnetic
field strength as well.

Regardless of the specific type of yoke you are using, these values need to be as correct as possible or the yoke will not give the desired results.


I have acquired every part save one which is required for me to build a magnetic coil charging apparatus similar to the one used at
VDC for calibrating focus yokes for new Marquees. Once the giant toroid is rewound to the appropriate specs it will be time to
build the rig and then I will be able to adjust most any focus coil assembly's magnets to the optimal range of strength.


I have now begun experiments with G90 focus yokes, which are the longest focus yokes of any I have yet seen. It is my opinion,
going into this, that longer focus yokes have an intrinsic advantage in terms of quality of beam control as they produce a longer
magnetic field path, giving greater beam control with less beam scattering and a beam distribution pattern that is sharper and steeper
than a similar yoke with a shorter magnetic path.

It is for this reason that I think that G90 focus yokes are probably the ultimate choice IF they are remagnetized and rewound to optimal values.

My own experiments have shown that in every case, beam focus quality is better as the length of the magnetic field is greater. The
stock Thomson yokes have a short magnetic circuit path length and the focusing ability is limited and at best the grid or dot patterns
are a bit blurry compared to what you get with ANY of the Kanto-Denshi yoke types, which all share longer magnetic field path lengths
than the Thomson yokes. Somer K-D yokes are longer than others and they have proven to be better IF their magnetic and inductance values are in the right range.

We have heard (and some of us have seen for ourselves) that the G90's test patterns, when properly aligned, look like they were drawn
by a laser. I think that it is these super quality long throat focus yokes that are mostly responsible for that.

I think that I just triggered a stampede for any available set of G90 focus yokes, just in case I'm right. But that's OK because I have
my set already, safe and sound. I'll be sure to publicize my test results as I go along.

Of course, the G90 focus yokes are very long. This may create space issues on the neck. For that, I suggest that it may be possible
to use Sony G90 deflection yokes (which also have integral convergence coils in their structure) if they are electrically compatible with
the deflection circuitry of the Marquee. As the Sony deflection yokes are also very precisely made, and in fact make the stock
Thomson yokes look decidedly second rate when compared side by side, I do not think that you will LOSE any performance with the
Sony deflection yokes, presuming that they are compatible to start with. The Sony deflection yoke assemblies are shorter by a
respectable margin, compared to a stock deflection and convergence yoke set.


Incidentally, I also have a set of the G90 electronic CPC rings to play with. Small DC voltages, carefully applied and adjusted, should allow them to work properly in a Marquee. No twisting of CPC rings required. All done with a few variable pots and DC power supplies.

But that's another project.


CJ

[mp20748]

[mp20748]

CJ,
the Stig coils will need a waveform in order to do what it supposed to do well. So you'll need a wave shaping circuit in order to control the dots.

The Barco 909 has its electronic stig control built into the focus coil assembly. They are using very powerful focus and stig amplifier circuits to control both. Their 4 pole centering/stig ring makes perfect sense to me. It allows you to manually setup both centering and stig using magnets, therefore allowing very stable initial centering and stig control without using any electronic control circuits for the most critical part of a very good and stable setup.

There's always a lot of discussion about focus and what's the best focus system. Considering the time these projectors were put on the drawing board, the highest usable (really) scan rates were either 1280x1024 or 1600x1200. Neither really required the bandwidth that 1920x1080P 60hz requires today. So the focus system regardless of how good it is/was, it had to compliment the bandwidth capability of the projector. Meaning, the focus is only important when it also involves true display resolving power.

So if a CRT projector can focus a perfect test or dot pattern, but not be able to properly resolve the usable higher bandwidth of the higher scan rates of today, there's no real benefit of having a super focusing projector.

Today, everything high performance is also HIGH Definition. Or to put it another way; Highly Defined video.

To highly define todays video you'll need a ton of good and clean bandwidth...and no focus circuit regardless of how great it may be, could ever get you around bandwidth requirements.

Proper bandwidth requirements and great focusing go Hand in Hand -- Neither is great without the other...

[Mark_A_W]

I'm sorry Mike, but how is 1920x1080p at 60hz so different to 1600x1200 at 60hz?

1080p is about 10% higher pixelclock/bandwidth needed. No huge difference.

And PC usage requires far more sharpness (particularly in the corners) than video does.



I don't think the requirements have changed at all. The only real difference is the 16:9 aspect ratio.

[mp20748]

The flatness bandwidth of the three mentioned scan rates is:

1280x1024P 60hz = 53mhz

1600x1200P 60hz = 78mhz

1920x1080P 60hz = 84mhz

Put all three one at a time on a display in their respective aspect ratios, and then see what happens when using the SMPTE test pattern.

[cmjohnson]

Just to clarify, all the "higher" model K-D yokes have astig coils in them and I do use them. They work very well. They are taped into place inside the central coil assembly on the KF-3203 and G90-type coils, in an array of eight coils in two phases, arranged equilaterally around the perimeter of the inner coil form. The Marquee circuitry seems to be quite happy to use them.


I think you misunderstood me. I was in fact referring to the G90's electronic CPC coil assemblies, NOT astig, which serve the same function as the little CPC magnet rings that most projectors carry. As the need here is for a STATIC magnetic pattern (or actually, three of them in the case where the CPC ring pack contains 2, 4 and 6 pole rings), then the electronic CPC coils only need a small DC voltage applied to them. It does not need to be modulated and in fact that is one thing you would NOT want to do.

Building a small power supply (or actually, several independent voltage feeds off a suitable supply) and giving DC to the electronic CPC
coils should be all that's required. But I would have to be able to control both the current and polarity of the voltages going through the CPC coils. Once the correct range of voltages, currents, and polarities is established, then at that point someone could look at the
odd but maybe workable idea of tapping the COLOR, TINT, DETAIL, and VOLUME outputs of the CLM to drive a variable DC-DC converter
so that those new adjustments could be made from the remote control. It wouldn't be the most complicated engineering project ever
but it wouldn't be for a beginner, either.

CJ

[Mark_A_W]

[mp20748]

[mp20748]

[Nashou66]

Paul, on my rewound barco coils removed the tightening ring and then snapped off the threaded fingers or tabs if you want to call them. then i took a rounded
rasp and reamed out the inner of the coil so the barco coil slides right over the convergence coil. the metal clamp on the front of the coils is enough to hold the whole assembly in place. the sony 1292 coils have no clamp on the tube side. it is flat.

Athanasios

[cmjohnson]

Mike, I don't have that particular Barco coil. I do have G90 CPC coils, though. I think that they serve the same function, don't they?


CJ

[zGman]

G90 and 909 both have 4 and 6 pole astig...all mounted in the "focus" coil assembly.

This seems like a great idea until you start to figure out how many more zones
you get to set up....hohoho!

The G90 also has a separate "cpc" electromagnet ring mounted where the
little twiddly "cpc" magnets would normally go. I 'think' this is the mg focus
in the g90 menu. I do not know if this has zone adjustment, but Terry or Craig will.

G

[Mark_A_W]

[stefuel]

You guy's never cease to crack me up. I understand that with some of you this is a matter of how hard you can push it on test patterns but non of this will ever increase your percieved resolution on "full motion video". Perhaps if you're gaming on your CRT you might see some improvement but not full motion video.

[cmjohnson]

Yeah, but it's just like the quest for a faster car. Never mind that the speed limit is 70 unless you live in Montana, we'd rather have a car that can do 210 than 160, particularly if we can make the 160 MPH car reach 210 just by making a few adjustments here and there.

My own personal motivation is the discovery process and making something do its job a little bit better than it's ever done it before.

I'd rather have excess capacity to sharpen the picture than not enough.

If I'm able to fully resolve one on, one off pixels at 1080p-60 (or higher) then I'm pretty happy...but I'll run even higher resolutions for
final test, such as QXGA, which is 2048x1536. But to make matters more difficult, I compress that into a 16:9 format, which is the
same effective resolution as 2048x2048 in 4:3 mode.


Finally, I guess this needs to be mentioned: In my own experience, my belief is that the better optimized focus yokes may or may not
actually give greater resolution capacity in and of themselves, BUT, they do give a better MTF and beam power distribution profile than
the stock yokes. The stock yokes give a very classic Gaussian power distribution curve across the scan line, while the K-D yokes make the power distribution curve look more like a square wave and the power band is narrower and sharper than what you get with the stock yokes.

Line sharpness alone is no guarantee of higher system resolution but obviously it can be a limiting factor. A good sharp focused line will at least ensure that you can get the full rated resolution out of the projector.

Ideally, I want to have to slightly defocus the picture in order to make 1080p look absolutely perfect. Being ABLE to count the scan lines is not as good as just barely merging them, from a picture quality standpoint.

I was not aware of the existence of 6-pole astig coils in the G90 focus yokes. This is probably because the first one I've taken apart
is kind of jammed up. I can't pull the outer coil formers off the inner one easily and I don't want to damage the inner coils, so I've
never actually seen the inner coils.

I can't see any practical way to put the 6-pole astig coils to use in a Marquee. Not unless I can persuade someone at VDC to hack
a third channel into the astig system and help me wire it up!


CJ