CurtPalme.com Home Theater Forum

[tse]

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The magnet strength is indeed critical. If the magnet is too strong the focus is like when you are adjusting the CPC rings for "flair" (in the center of screen). If the magnet is not strong enough it is like when you are adjusting your dots to be round with the stig part of the CPC rings. The static coil winding is a fine tuning adjuster with only a couple of percent range from min to max. VDC adjusts the magnet gauss +/- 0.5% so the static focus is correct with the adjustment between 40 and 60. I can tell you that this is a royal PITA. You first saturate the magnet by charging it as much as it will go then apply an AC field to the charging coil to bring the gauss down to the correct value. A little too far and $*%## you have to start over.

As far as I know the Marquee system is unique in that there is a negative current in the dynamic winding when scanning the center of the screen. That is why the center focus is off when there is no dynamic focus current. It is only right when static focus current is nearly zero and dynamic current is negative. Most other projectors (if not all) have zero current in the dynamic winding when the center is scanned. Their magnets are set for good focus with zero current in both static and dynamic windings. This is why "frankenyokes" may not be perfect gauss for Marquees. After all, with the same CRT and same anode voltage and magnet same distance from CRT screen the same gauss is needed for focus.

Wow! That made my brain hurt.

Scott

[Nashou66]

[cmjohnson]

The advantage to the Frankenyokes, as we call them, is that, apparently, the design of the yokes that are candidates for the job, which are all various editions of the Kanto-Denshi baseline design, has certain advantages over the Thomson yoke. Those advantages include an intrinsically more even magnetic pattern as the structure is made up of ring magnets and ring spacers, while the Thomson design uses six bar magnets in a squirrel cage design, which allows for the possibility of the different bar magnets to be at different strengths and thus create a lopsided magnetic field. The K-D design is practically immune to that issue unless the magnets end up broken.

And, the K-D design has a longer magnetic field (going down the length of the neck) with different yoke types having different length magnetic assemblies. There seems to be a direct correlation between the length of that magnetic field area and quality of beam focus
over a broader range of contrast values. I surmise that the longer magnetic field is what allows this better controlled electron beam
across a wide range of contrast levels. The longer the field, the greater the effect. The G90 yokes are the longest yokes available
anywhere, and thus are potentially the top performing yoke for bloom-resistance and precise focus over the widest possible contrast range.

Tse has evaluated some FrankenYokes on his own test system, using the MTF measuring system, and found that the beam profile from
the FrankenYokes is more of a "square wave" profile than the typical Gaussian (sine wave top) profile as found with the stock Thomson
yokes. IIRC, he observed a noticeable improvement in spot size at normal contrast ranges, meaning sharper focus, and a dramatic
improvement over the performance of the stock Thomson yokes at high contrast ranges where the Thomsons start to allow focus blooming. And, it should be noted, the FrankenYokes he tried out were not optimized for the Marquee's circuits. They were the first
edition types made from 2211s which don't even have astig windings.


I'm literally days away from finishing up my first sets of optimized FrankenYokes. My hope is that Tse will have the time and the
inclination to drop them into a testbed projector and put them to the test, measurements of focus spot size over a broad focus range,
corner astig control, etc. all included. But that's for him to decide.

The Frankenyoke improvement in focus at normal viewing settings is not dramatic. But it's measurable. But at high contrast settings,
there simply is no comparison. These high contrast settings, with full clarity and no focus blooming, add so much more life and punch
to the picture that it would be hard to imagine that any real enthusiast wouldn't want a set. However, we know that the supply is limited.

I've looked into getting the magnetic parts replicated for making new ones. There are many ferrite and magnet companies that could do this...for a price. And that's the problem because the CRT market is many things but GROWING is not one of them. It'd be really tough to break even, much less turn a profit.

CJ

[mp20748]

[cmjohnson]

Yes. You'll draw less current and the focus module will run cooler if it doesn't have so much more to do by correcting for an overly weak or strong magnet, too. The magnets should be at a strength value which requires the least focus correction current.

Weak magnets (or overly strong magnets) will cause the focus board to have to work harder to overcome that error. Some examples
of yokes that have been tried out as Frankenyoke candidates won't even reach full focus. They would be very hard on the focus amps.

I'm pretty sure we've all seen grid alignment shift with focus adjustment changes when the focus system wasn't perfectly aligned.
I believe that this shift is greater when the focus system is already working hard to overcome an improper strength coil magnet,
which is the case with most Frankenyokes. I've found that Frankenyokes are touchy about magnetic alignment, and I think that
this is the reason. My belief is that a set of Frankenyokes that has been optimized to Marquee values will give all the benefits
and none of the drawbacks. Less shift, sharper focus, wider range of contrast with good focus.

CJ

[dvh99]

parts came in today.
i have been thinking about the aoyue a long time now and the guy who owns the pj and i have bought it together to share costs.
this is the 1 we bought, i think this will work like a charm at least i hope it will.



2702 model.

without such a device i am not changing out dip cases.

[Nashou66]

They are fairly good units. Buy another iron as when you put any pressure on that one over time it breaks, only bad point.

The Hot air wand is the best thing about that unit, so versatile.

Athanasios

[dvh99]

fixed .
changed out the 9 irf520 fets and 3 2n7000 transistors and that already did the trick.
the aoyue works perfect, i can recommend it to everyone.
now to change out all the el caps and the tle 2074s.

nash you were right again.

[Nashou66]

[dvh99]

the pj is now completely setup and it has run 8-10 hrs without any problems so far.
we watched chronicles of narnia (great for colours and black level) and the picture was stunning to say the least.
i never saw a pj with 3 lcps cause my green is a pt22 and with contrast on 60 it was amazing with a very 3 dimensional picture.
i encountered 1 other minor problem with the remote responding very badly but after cleaning the pcb of the remote it worked as new.
for the astig i took another approach, i just looked into the tubes while twisting and turning the cpc magnets and this worked much better than watching at the screen and did the same with el astig.

dennis