CurtPalme.com Home Theater Forum

[cmjohnson]

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I've been getting a lot of questions about the "Frankenyoke" focus mods I've
been working on for Marquees.

Rather than answer the same questions over and over about the same thing, the
purpose of this post (and maybe more posts in this new topic) is to put all this
information together in one place.


Here's a brief synopsis:


Frankenyoke MARK I

The original concept, which I called the Frankenyoke, started out as a matter of
pure curiosity about other forms of focus yokes that could be used in a Marquee,
as I thought that the standard Thomson focus yokes are only fair and could stand
to be improved. It was only a hunch.

I decided to try out the yokes that AmPro was using in their projectors, which are
made by Kanto Denshi, and as I understand it, are no longer being made by
that company. Whether or not the company even exists now is a question I don't
have an answer for.

The type of these yokes in question is KF-2211 by the label that's usually found
on them.

They look like this:





The item on the upper right is this type of yoke.

The item on the upper left is this type of yoke removed from its shell.

The item on the lower right is the standard Thomson yoke used in a Marquee 8000.

The item on the lower left is this type of yoke removed from its shell.





What I did with this type of yoke is to take an old stock yoke from a Marquee
8000, disassemble it, cut the wiring harness off it, save the shell, and toss the
rest of the original yoke in the scrap bin.

The wiring harness from the original yoke is attached to the KF-2211 yoke
exactly as pictured here:




PLEASE NOTE THAT THIS PHOTO IS NOW THE CORRECT VERSION.




In order for you to do this, you will have to unsolder and remove the white
four-pin connector.

The yoke is now placed into the Thomson yoke shell and secured in place with
hot melt adhesive. But be sure to put it in in the proper magnetic polarity.
In order to be sure what that polarity is, hold it near another stock Marquee
yoke that has not been disassembled before and is in factory condition.
With the two yokes aligned in the same direction, going end to end they should
attract each other magnetically. If they repel each other, flip the coil over and
try again.

You MUST get this right. Do it wrong and it will probably destroy a tube.


The internals will FULLY fit into the Thomson shell. Be sure to center the yoke
core very carefully in the shell before securing it in place with hot melt glue.

Use an original yoke as a reference to get the bolt locations right.

The functionality of this yoke is exactly the same in every respect as the original
Thomson yoke but it will give respectably sharper focus. A sample of this new
type of yoke has been measured professionally and achieved a respectable
rating of 11 percent MTF at the resolution of 2048x2048 using standard SMPTE
test patterns.

It'll smoke any 1080p test pattern without even breaking a sweat, IF you have
taken the time to do your alignments properly.

This is not a magic yoke. It is every bit as demanding of proper setup as any
stock yoke, or perhaps even more so. But the rewards are a picture that is
sharp beyond all reason, if coming out of a Marquee 8000.

This yoke type lacks electronic astig windings. If you put them into an 8500 or
9500LC, you will lose your electronic astig feature, but honestly I don't think it's
much of a loss. The corners end up so sharp that I don't think you'd miss that feature.

Another VERY significant attribute of this yoke is that it exerts much greater
control of the electron beam at higher levels. Throw up a test grid and crank
up the contrast, and the lines in the grid hardly spread out at all. The lines don't
get wider, they just get brighter. This is a remarkable level of control vs. the
stock Thomson yokes, which tend to lose control at higher contrast levels.

This equates to a sharper picture at higher contrast levels.

Sample photos that I took of this attribute: Note the contrast numbers.





You're not going to get that sort of control with the factory yokes!



Phase II: Frankenyoke Mark II

But I did want to come up with a second generation Frankenyoke, the
Frankenyoke Mark II, which would offer similar focus performance and adds
electronic astig correction. After some searching, I was successful and got a
set of yokes from a Sony VPH-1292. As most people do not opt to retube 1292s
due to the extreme cost of the tubes, these are sometimes available on the
used market. These yokes are made by the same company and SOMETIMES
bear a part number of 22-22.

Some other projectors may use the same type as well. Look for the same
physical type and NINE pins on the white connector.

They're a bit longer than the 2211 coils, so they don't quite fit in the Thomson
yoke shell.

They look like this:




You have the option of leaving them in their original shell, but if you do that, you
will not have the raster centering feature that is one of the nice features of the
Thomson yoke design.

My first prototype Frankenyoke Mark II was built by me splitting the two glued
together halves of the "lid section" of the Thomson yoke and using just one of
them, along with some 1/8" spacers between the "lid" and the shell. I may
try something different. I want to presrve any functionality that actually
matters in a Marquee but want to keep the yoke length as close to original as possible.


The wiring of the Mark II yoke is achieved by using the harness from a stock
focus yoke from an 8000 (Please do NOT sacrifice a yoke from an 8500 or 9500,
with the astig wiring harness, as those are valuable!!!!) and the astig harness
that I use is the harness taken from a retired convergence yoke from any
retired Marquee. So the new focus yoke will have TWO wiring harnesses coming
out of it, and the second one of them has just four wires and looks just like
your convergence yoke's harness. Be aware of this and don't get them mixed up!


The Mark II yoke looks like this after wiring it up:




Yes, you will also have to remove a connector from the little PC board.

Make sure your completed harness looks just like this photo. It's clear enough
that no written instructions should be needed.


Magnetic phasing of this yoke type is ALSO very important. Put it in wrong and
you will probably take out a tube.

Fortunately, these yoke cores are easy to figure out. If you leave them in their
original shell, they only go in one way thanks to a locking tab on one end, which
is also usually painted with some red paint.

If you opt to use a Thomson yoke shell, the red paint and tab are on the side
of the shell that is wide open and that you will cover with the lid.


Be careful to check the polarity against another untouched factory yoke, though.

And if using the original yoke shell, make sure you install it in the correct
magnetic polarity. It must be the same as on a tube with an original yoke on it
in the factory orientation.

Now, this can cause a little confusion, because I BELIEVE that this means that
you will be installing the yoke on the tube in the OPPOSITE magnetic polarity to
how these yokes are installed on AmPro projectors, but as I have not looked
inside an intact AmPro projector in a long time, I can't attest to this with any
certainty. But if this IS true, then the absolute magnetic polarity doesn't
matter, so long as it's the same for all three tubes. I want to check with
someone who's more experienced than I am about that before I confirm that,
though.

IF the absolute magnetic polarity doesn't matter, then you would be better off
to install the new Mark II yoke with the clamp screw facing toward the back
end of the tube, as this allows the yoke coil to be closer to the bell of the
tube, which gives better focus.


I'm thinking about it, and my OPINION is that absolute magnetic polarity of
the yoke isn't critical, but all three yokes in the projector must be in the
same direction of polarity.


With the yoke installed as well as the rest of the magnetics, which of course
means the CPC magnet pack (and if the pack doesn't have 2, 4, AND 6 pole rings,
get one that does have all three!), and then plug in ONLY the focus coil. Turn
the PJ on and do your magnetic alignments, BEFORE you plug in your astig
winding. Then start adjusting the stigmators.

I think you will be very impressed at how much better the astig feature works
now. These yokes are so much better in the way their astig coils function vs.
the Thomson yokes that it's like switching from stone hammers and flint knives
to a really good set of tools and fine chef's knives.


In my opinion, both the original Frankenyoke and the Mark II version are capable
of delivering focused images that are beyond the ability of the air-coupled HD-8B
lenses to do full justice to. Those lenses simply can't resolve the detail that can
now be focused sharply on the CRT face, especially in the corners, and only
an LC machine with HD10 family lenses (and possibly an 8500 with HD-144s or
145s) can really resolve all that these yokes can reveal through their excellent
sharpness and detail.


I HAVE tested the Mark II yokes in a Marquee and found the results to
excellent. Focus is every bit as good as it is with the Mark I yoke, and
with the added astig correction, it's even better, especially in the corners.
I use very fine text as my final test pattern when aligning astig. When
readability is maximized, it's set up as well as possible.



I'm giving you all the info you need to make your own yokes because I'm not
planning to make a business out of it. I figured this all out for my own benefit
but I see no reason not to share the information.



You want a set? You need to first, find the appropriate yokes for your need.
2211s or 22-22s. Don't let someone rip you off for them, either. I would not
pay 50 bucks each for them on the used market.

Also, you will need a donor Marquee 8000 yoke for its shell and cable, and a
donor Marquee convergence yoke for its cable.

Again, I ask you NOT to sacrifice a Marquee focus yoke that has the astig
winding on it due to its greater value. (If it has a blue wire, it's the type
with astig windings. Keep it or sell it, but don't cannibalize it.)


Word of warning: Any hardware you use to hold the new yoke together must
be made of NON-MAGNETIC materials. Brass or stainless hardware only.
Or nylon, if you trust it enough.


CJ

[JustGreg]

Awesome CJ!!!! I'm not a very pj savvy guy yet but a pic is definately worth a thousand words.
I've been following your work closely for the better part of a year and it appears you've plugged the biggest hole in the edge-edge design gap on the 'Quees display capabilities. The only weak link left is the optics....which is a relatively easy and inexpensive bolt on fix with the right lenses.
Inexpensive and ubber cool enhancement dude! I'm psyched! Take a bow.

--Greg--

Now all I need is to gather the goods and catch you in the midwest to install and dial the suckers in for me.

[cmjohnson]

Lenses are EASY to handle! Got 30 grand you want to loan me so I can
put a set of Surfbird 1s on a Marquee? (Yeah...they're about ten grand each!)

I hope to add some SERIOUS resolution-revealing photos very soon. I want you to see
the astig functionality of the new Mark IIs, which is so precise it's incredible.

I'm getting pretty confident that what Mike Parker has done for the performance of the
video chain, I'll soon be able to equal in terms of performance upgrades to the focus
and sharpness aspects of the picture. My focus is on focus and the ability of the
tubes to resolve all that they can, as sharply as possible. I leave the gamma, color
tracking, grey scale linearity, and signal bandwidth part of it to Mike and others who
are good at it.


What I'm hoping for is that when these are well proven mods, they'll be crossed with
Mike's best mods and together we'll make the Marquee that drops EVERY jaw to the floor.


This just MIGHT shift the "most valuable projector" trophy away from the Cine 9
or the G90 and to the Marquee. it's too early to do a shootout YET, though.


We'll be ready for the next generation of ULTRA High Definition before it even exists!


CJ

[JustGreg]

Yup. What you said...you Mad Scientist you! I'm glad you brought up MP and those like him. Everybody involved in this "hobby" such as Greg E, Moon Jong, moomee, and the others (sorry..can't recall you all now) are just as important to the hobby. And even as I call it a hobby, CRT products and support is STILL a thriving business. Even THOUGH, the majority of former CRT pj manufacturers have abandoned that product line and moved on. Amazing.
T-coders, scalers, HD devices; they all consider RGBHV in their designs for new products. Talk about backward compatible thinking. Manufactuerrs WANT to cut RGB support...but they don't dare. They are impelled to go back over 20 years when considering the designs for their "cutting edge" products. They're afraid to cut RGB because they know what we know...
CRT projection for the new millenium......It ain't dead...it's just been napping and waiting to be recognized.

Again...I'm impressed and can't wait to come up with the $$$ to have a 3 tube pj that's as good as your single tube test bed machine.

--Greg--

[cmjohnson]

The original FrankenYokes are running in a complete 8000. All three tubes, baby!
Running beautifully at resolutions far beyond what it was ever intended to run at.


1080p native is the high water mark for digital projection outside of 2K theater
DLP units. I've only heard RUMORS of any higher resolution display device than that
in terms of production equipment and not prototypes cooked up in a lab somewhere.

Is there a 4K or better digital display?


What's the highest resolution that most video card can display? 2048x1536, QXGA.
What digital display can you buy that will handle that without downrezzing it?

NONE. Only CRTs go that high.

I don't know how far out I can push these yokes yet, but I think that on a 9" tube,
I'll knock down 2500x2000 with a respectable MTF reading before long. Maybe
even more than that.

At the ragged edge of resolution capability, there is ONLY the CRT.


incidentally, I've seen some special purpose CRT projectors that make the very best
of anyone's efforts at finer beam focus and resolution capacity look like a child's toy.

Think about displays that can fully resolve 30 megapixel images. I've seen them.
They're NOT listed in the regular product catalog for the company that makes them.

Industry trade shows are fascinating places to go, sometimes. I'll be at the
I/ITSEC show in December, in Orlando, FL. There will be a lot of display products
on the tables being shown off. I'll probably see stuff that will make any videophile
drool uncontrollably.

CJ

[AnalogRocks]

Two questions

. If you were to do this to the yokes with the astig in them wouldn't that be the "NEXT STEP" up in Franken yoke design?

If you made one of those yokes would the astig corner focus function still work?

[AnalogRocks]

Two questions

. If you were to do this to the yokes with the astig in them wouldn't that be the "NEXT STEP" up in Franken yoke design?

If you made one of those yokes would the astig corner focus function still work?

[cmjohnson]

Frankenyoke Mark I does not have astig. It still give excellent corner focus. It's so good that you may not miss the astig function if you had it before.

Frankenyoke Mark II DOES have astig and it works phenomenally well.

My intent was to make that clear in the initial post. I will edit that post to make it
even more clear. I want to get this explained to the point that all your questions are
answered in the first post.


CJ

[cmjohnson]

I have an update.


I tried installing one of the Mark IIs while still inside its original shell. By doing this
you do lose the ability to offset the yoke for centering. I haven't fully explored the
implications of this yet, but it seems to be just FINE so far. I won't know until I've
installed all three if losing the offset capacity is really a handicap.

I'm inclined to think that it's not a handicap to lose this feature as these yokes are
apparently much more uniform in the distribution of their magnetic field than are the
Thomson yokes, which rely on 8 magnets spaced between two rings in a squirrel
cage type arrangement. If the individual magnets vary in strength, it will cause
beam offset all by itself, and I've seen a few such yokes that had to be offset to
their limits to get the beam centered properly, which I've NEVER thought was right.

I'm of the opinion that the Kanto Denshi design yokes are naturally superior at centering the beam in the tube and don't NEED any offset. But I have more
exploration to do before I'm ready to back that up.

I'll say this, though: The more I learn about these yokes, the better I like them.



CJ

[AnalogRocks]

[AnalogRocks]

[cmjohnson]

I've updated the harness photo in the first post. It's now correct.


Further news: I've decided that there is little point in investing a great deal of time and effort into fitting the Mark II yoke into the Thomson housing as the diameter of the core of that yoke is significantly smaller than the diameter of the 2211 yoke core,
so there really isn't much lateral offset available. I'd go so far as to say that the max
offset that's possible with this core is so little as to not be worth the effort. As a result, I'll be mounting the test yokes in my own 9500 using their original Kanto Denshi housings. This means that the mod has been reduced to adding the
Marquee focus and astig wiring harnesses to the K-D yokes and putting them in.
You don't need the Thomson shell but you still need the cables.

Of course, you are more than welcome to mount them in Thomson shells if you
want to, but the benefit of that design, lateral coil shift, is mostly negated by
the smaller diameter of the coil.



CJ



CJ

[cmjohnson]

I must note at this point that I've been making a lot of observations about
the performance of these yokes and must conclude that they're a bit
quirky and the cure for their quirky behavior may be to make some minor
mods to the focus board.

The inductance value of the yokes is sufficiently different that it seems to
be causing changes in the function of the focus circuit, which is a resonant
circuit which the yoke is part of.

Some component value changes on the focus board are probably in order
so that the performance of these yokes may be optimized.

What I'm seeing is a persistent inability to get the central and left side
sections of the raster (in tabletop mounted configuration) to focus at the
same time and to the same level as the right side. And focusing
changes made to the right side also have an effect on the middle region.

The issues are related only to horizontal position, not to vertical.

But even as things stand NOW, even with this fairly subtle problem
holding things back, the focus is STILL better overall than the Thomson
yokes deliver.


I hope to have a focus system mod worked out VERY SOON to allow optimal focus with these yokes.



CJ

[grae]

Would the yokes from a G70 work with this mod? I've got spare projector that I was intending to use as a parts machine. Also, a 8000 that I think has a bad hpvs.

It's really impressive what you've done. I wish I had the technical know-how to do the same.

[cmjohnson]

I'm learning a lot as I go! I really didn't know anything at all about how the focus system operated except how to run it with the PJ's remote, when I started.

Now I'm beginning to understand it well enough that I think I know where to focus my thoughts and tests in order to make it operate optimally. Some parts are gonna change in the focus board!

But yes, I'm still shooting in the dark a bit. I'm definitely riding the learning curve
and am not ready to say I know the circuit very well. Because I truly don't.


I've heard that the G70 focus coil won't fit on a P19 size neck. Can you check it?
The neck is 1.5 inches wide so the center of the coil has to be a tiny bit bigger than
that, at least.

If the coil itself is big enough but the plastic shell isn't, well, they can be put into
different shells.

Can you put up some photos of the G70 coil, showing the connector in at least one photo?


CJ

[cmjohnson]

I learned a lot about the theory of operation by finding the original US patent document in a search.


The light is coming on.


I think I know what to do....and calculate the values of the caps to change.



CJ

[cmjohnson]

If I did my homework right, the static focus coil's associated capacitor needs to be roughly doubled in value. The dynamic coil's caps are within 12 percent of their
optimal values so it's probably not worth it to change out those four caps.


So one measly capacitor is all I MAY need to change to make these yokes completely
happy in a Marquee.

I may have that answer tonight.


CJ

[cmjohnson]

No answer tonight, but I DID fix the LVPS in my Tektronix 2430 o-scope so I'm
better equipped to explore the focus circuit now!


CJ

[cmjohnson]

Time for an update.

I'm more convinced than ever that these yokes have fantastic potential BUT they will only
achieve that potential via some additional mods.

The problem is that the static winding of these yokes has only about HALF the inductance
of the Thomson yokes, which creates a problem in that the focus board can't quite deliver enough power to bring the focusing field to the strength
it should be.




The options are to mod the static focus coil itself or mod the focus board.

I'm pursuing experiments in BOTH directions. I think that rewinding the static focus
coil is overall probably the easiest answer. I've already taken one coil apart, measured
it in all relevant aspects, and calculated the new wind for it. I just need to lay my hands
on a spool of gauge 32 magnet wire and I'll be running the rewound coil very shortly.

The other approach is to change the drive levels in the static drive amp, which is more of a problem as I'd have to mod the LVPS to increase the
available rail voltages. That's pretty much out of the question.

At the moment, I'm inclined to believe that rewinding the coil is the better approach as it
will then make the coil have the electrical specs that the focus system is designed to run at,
if I wind it right.

I could have a running rewound coil as early as tomorrow, with any luck.

CJ

[cmjohnson]

Here's a series of shots of the insides of the Mark II focus yoke assembly.











It's a magnificent design. The astig core is the innermost core, closest to the CRT neck,
which explains why its functionality is so crisp and precise.

The two outer cores, yellow for static and red for dynamic focus, are relatively long
as is the total magnetic field, which helps explain the stability of focus over a wide
range of contrast settings. The stock yoke's dynamic and static focus windings are
both less than a quarter inch thick. The longer coils work better.


I'm rewinding the static focus coil to more closely approximate the electrical
parameters of the Thomson yoke's static coil, which should be the solution to making
the focus system work properly.


CJ

[Joust]

[Joust]

[cmjohnson]

Because the Thomson yoke design SUCKS!

You can't polish a turd.


It's the length of the coil in the magnetic field, and the length of the field itself,
that is mostly responsible for the superior beam control given by the Kanto Denshi
yoke design. The individual dynamic and static focus windings are an inch wide,
roughly, compared to LESS than a quarter inch wide windings on the Thomson
yoke, with a shorter magnetic field, which is an inferior design when run over
a wide range of available contrast.


Match the Marquee's electrical parameters to the parameters of the K-D yokes
and you have the best of both worlds. But it's easier for me to rewind one coil
than it is to redesign the static focus drive circuitry.



Something came up yesterday that made me stop and think. The yokes may not NEED rewinding....on SOME Marquees. I think the difference is which HVPS type is in the unit. I'll be testing that theory TODAY. If I'm right, a Marquee that has the 34.9 KV HVPS can work with these yokes NOW, but the coil will have to be rewound if you have a 34.0 KV HVPS.


I'll know later today.



CJ