CurtPalme.com Home Theater Forum

[barclay66]

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[stridsvognen]

[barclay66]

[Nashou66]

I think its the focus system for the Marquee. I had a Green used LUG here that when using the Sony coil
with no connection I got a better focus than the marquee coil no connection, that is I tried them in static mode.

The LCP's focus better with the marquee coil no connection. If you have a barco or sony style focus yoke give it a try to confirm my test. I did this after Curt said he had issues with the LUG's in marquee's.

But I don't understand why VDC sold marquee's with LUG's as an option? maybe they did do something special on those VNB's?

or maybe they only began selling them with the new style VNB's Scott designed?

Athanasios

Athanasios

[greg9518lc]

Nice to see we now have mod options for Lug tubes on the Marquee from MP.
And the stock coils and magnetics are fine with the new neck boards.
Now if we can get rid of raster ringing,blue gamma circuit, and
projector turn completely off if I am missing anything on the wish list feel free
to chime in

[cmjohnson]

Spot size is completely unrelated to the neck card. The only function of the neck card is to provide a means to vary the beam drive current.

Spot size is strictly controlled by the characteristics of the electron gun and the focus system. The neck cards has nothing to do with it, and CAN'T have anything to do with it OTHER than cause smearing of the flying spot if its transient response is not adequately fast and clean. And that isn't even a spot size issue. That's just temporal smearing caused by a lack of adequate transient response or an inability to sustain beam current levels at higher average picture levels (APL) if you're having issues with bright edges next to areas that are darker than they should be.

The "new" neck cards are not equal to the old ones. They aren't NEAR as good and even Scott, the designer, will be more than happy to tell you all about that little bit of truth. They're good enough for their simulation customers, but not as good as any health 2039 or 2038 series neck card. They don't have the bandwidth and they're not as linear in greyscale tracking.

I'll say it again and I'll be backed up by every engineer at VDC or that has ever designed a video neck card circuit: Neck card circuits can not affect beam spot size.

[greg9518lc]

Guess you should do a little more research looks like your not in the loop. Any lug tubes in a VDC is junk without mp modded neck boards end of conversation.

[greg9518lc]

Damn CM didn't bite? I have 9 sets of new neck boards to get rid off.

[cmjohnson]

I'm aware of the mods required to run LUG tubes in a Marquee. I have the parts to do that, and will be modding a set shortly.

Most of the Marquees delivered in the last few years of production shipped with LUGs and they are very sharp machines, and
I have plenty of examples of VDC modded neck cards as well as, of course, lots of stock cards, plus I've been following what Mike has said about the matter. Interestingly, they are provided with the "stock" values of 330K on pins 6 AND on pin 7, pin 7's
resistor being the one that Mike suggests needs changing.

Next to pin 7, change the R38 330K resistor to something much bigger to control that extra grid. Mike has experimented with up to 4.7 Mohm resistors, so I'm using 4.7M resistors myself at this point. They're cheap enough, about 2 cents each by the hundred.

Of course there's the flying lead change, remove socket 6 and drill it out.


The point is, while LUGs require you to make some mods to run them at their best in a Marquee, VDC actually hasn't been
changing R38 yet unquestionably their LUG equipped projectors deliver a sharp image, even though it may not be as sharp
as it COULD be.

So, yes, I guess you can say that the neck card can affect sharpness, but it isn't magic, it's just a matter of getting that extra grid on pin 7 under control, and that has nothing whatsoever to do with the video amplifier function on the card.

Silly me, I forgot to check and see what value resistor is on the new neck cards that ground pin 7!

If it's much bigger than 330K then I can understand why they may be perceived to be sharper with LUG tubes. Because they'd be controlling that extra grid properly.

I have not yet taken my large-ish tube testing, retubing, and upgrading project to the point where I'm doing full-up testing
on LUG equipped 9500LC Ultras and seeing what kind of performance they are capable of. But that day is coming. I'll be
able to, at my option, do some tests between various tube types and differently modded neck cards and SEE the differences
for myself. Put three green LUGs in one projector, with three differently modded neck cards. (Stock, resistor mod, full MP modded) Compare LCPs to LUGs with the same cards. Whatever I want to do.

When I get to that point, I'll let you know and show what I'm seeing.

[cmjohnson]

Content redacted as I need to verify it before reposting it. Don't want to post anything that might actually be wrong.

[greg9518lc]

I wish you all the best with your testing I am sure with your accolades with the Marquee you are the only one that is capable of fixing the neck boards for lugs.I can't wait to read your findings as it is so black and white with you. Maybe you can add value to all my new style neckboards. You could start by posting smpte patterns on your progress. And screenshots of images of your success. It will be easy to see how far you come. Since the screenshot thread has improved over the years and the bar has been raised over and over again by MP. Since you swear by different yokes show us all some results so we can buy into this claim they are needed. I hope wolfman gets it all sorted out to support your claims. Maybe he can help you test your neckboards and verify your findings. I am on your side wanting to see progress for the Lug and Marquee but sometimes you should stop preaching and start producing instead of justifying your view on the forum. Us end users are watching good luck.

[cmjohnson]

The smell of sarcasm is very strong all of a sudden.

Well, that's fine. Even though you are implying that I am suggesting things I have never suggested.

The nice thing about this is that we are ultimately dealing with technical matters that can be measured objectively, and when
those measurements are made, using logically acceptable procedures and measurement conditions, then the results will not
be subject to argument or opinion.

I think Wolfman's experiments are interesting but my approach to that issue is to emulate the most successful application of
magnetics to the CRT that any of us has seen, that of the 909/Cine 9, to the Marquee chassis. With those delivering rated resolutions beyond any other projector, with the same CRTs, then I believe that there is something to be gained by adapting
the same magnetics system to be driven by a Marquee. Which will require modifications not just to the magnetics, but also
to the deflection and focus systems to recalibrate them to complement the different inductance values in those magnetics, with the ultimate goal being to bring the electronics and the magnetics back into the resonant state that the Marquee was designed to use.


Frankly I have done enough research, both individually and with the help of some very accomplished EE's who are friends of mine,
to have little interest in the "new" VDC designed neck cards. There is simply no chance that they will be able to equal the bandwidth performance of any "classic" neck card equipped with the MRF 548 and 549 power transistors. So they are of no interest to me, although I suspect they can be improved beyond their stock state.

And there is no currently available, reasonably priced RF PA device which has the voltage rating, output rating, and bandwidth rating that would be required in order to make ANY bandwidth improvements beyond what Mike can get out of a 2038 or 2039 series neck card. While such devices DO exist, they're about 600 dollars EACH and it'll take a minimum of two of them for one neck card. Do the math. I'm not going to buy 3600 dollars worth of RF parts (not counting ANYTHING else as part of a proposed new neck card) for a single projector.


Modding neck cards aside from the simplest changes is not my thing anyway. I totally defer to MP for that. It's his field, not mine. Other people can identify what needs to be done, and I can follow those discoveries and do what they suggest, but I am no innovator when it comes to neck card circuitry and not once have I ever indicated that I am.

When it comes to the LUG tubes issue, I am seeking a better understanding of how that extra grid interacts and affects tube performance. I want to know WHY a change in the value of the resistor grounding that extra grid alters the picture qualities, and HOW they are altered. Which I freely admit, I do NOT know right now.

Far from being an expert, I'm always trying to learn something. Part of learning is to discuss the matter, and that includes discussion of planned and proposed experiments to see what happens.

[cmjohnson]

I'm starting to understand the function of the extra grid in a LUG tube now.

It's the last component of the electron gun that has a connection to the outside world. The beam passes thru it, and it has a certain amount of capacitance between it and other electrodes in the tube.

That capacitance is important, because capacitance affects frequency response. If you have any training in electronics theory, then you know that you can reduce the effect of capacitance on frequency response by adding a resistor in series with the capacitance. (C circuit vs RC circuit.) The higher the value of the resistor, the less the frequency response is affected.

That is why the value of the resistor that takes this element to ground should be large. The larger you go, the smaller the effective capacitance of the extra grid will be.

But there is more to understand. Every component in the electron gun assembly picks up an electrical charge due to the simple fact that the electron beam is passing by every part, and some electrons contact every part. Given time (and, not much) then the components build up a charge. That charge can be several hundred volts, and this is why even unused pins in a CRT need to be grounded, either directly or thru a resistor, both for safety and to avoid unwanted interactions caused by a component in the electron gun assembly that has picked up a static charge and by doing so is now able to affect the performance of the electron beam due to electrostatic forces.

If you ran with NO ground resistor at all, the extra grid would soon reach the full charge potential that is possible in that location in the neck of the tube. Not sure exactly how much that would be, but it would probably be several hundred volts, and may be enough to arc over to nearby components and damage the neck cards.

If you have ever run a Marquee with the G2 pin disconnected, you are seeing an analog of what happens, but to a more dramatic and potentially tube damaging effect. Disconnecting G2 allows the G2 grid to float up to the electrostatic potential of the electron beam in the tube, and in this state you have no control over the G2 level and thus no control over brightness. Which, now being equipotential with beam voltage at that point, will be several hundreds of volts.

Without having a similar method of controlling the extra grid (G3) on the LUG tube, it, too, will float high and although I'm not inclined to actually test it, I believe that if you were to remove the grounding resistor from pin 7 then you would probably get a dim and/or poorly focused picture.

With a high electrostatic potential on the grid, it would also affect beam shape and current flow, and apparently, not for the better.

So we do want to ground that grid. But not straight to ground with a zero ohm resistor. Actually, the value of the resistor will directly affect the voltage that the grid operates at. The higher the resistor value, the higher the grid operating voltage and the greater the electrostatic charge and effect on beam shape, and, presumably, beam current as well, as it does function as a valve.

The lower the resistor value, the lower the operating voltage of the grid, and the lower the electrostatic charge on the grid,
causing presumably less effect on the beam. BUT....at an increase in current thru the grounding resistor. If you went too low on resistor value then you would need to upgrade to a resistor with a higher wattage rating. Bleeding off this much energy from the electron gun assembly would probably have other detrimental effects on the qualities of the electron beam as well.

I still don't fully understand it, but the light's getting a little bit brighter. Electron gun assembly is a speciality science unto itself and so far I am barely even scratching the surface.

But at least I can begin to understand how that extra grid can have an effect on beam spot size even though it isn't connected to an external voltage source, and is in fact grounded.

It's because it's connected to an INTERNAL voltage source, the electron beam itself, and by controlling the rate at which it bleeds off extra electrons thru the grounding resistor, we can control its electrostatic potential and current flow to ground.

[cmjohnson]

FINALLY I've started full projector testing on my first rebuilt Marquee using LUG tubes.

I'm using Mike's suggested 4.7 megohm reistor mod on R38, along with a few other basic mods to the cards, and
I'm seeing some impressive sharpness but I haven't done more than rough in the magnetics yet.

Since the tubes can be considered to be new for all intents and purposes, I started out with brightness and contrast backed way off,
and still had to readjust the color temp settings to drop G2 and drive lower.

One thing that I saw, which I've seen before and never bothered to comment on, was that with G2 up too high, and turning brightness and contrast down, I saw the internal grid pattern appear as a negative image. Darker lines on a lighter background.

I find that to be an interesting phenomenon. I need to think about it to try to understand how that can happen.

[cmjohnson]

I had a conversation via email with Tim recently and it has turned the light on.

As I believe things to be now, the Marquee was originally designed to use Thomson CRTs and magnetics.

The Thomson CRTs, as you MIGHT remember or know, ran at 40 KV anode voltage and the Marquees had 40KV HVPS units in those days as a result.

Thomson provided the focus and deflection yokes to work with those tubes.


At some point, Electrohome switched to using Panasonic (MEC) tubes but they did NOT re-engineer the projector more than they had to in order to make the MEC tubes work, which was to lower the HVPS to 34KV (later, 34.9 KV) and build new neck cards as well.

What they also did not do, which set them apart from EVERY other CRT projector manufacturer using MEC tubes, was to follow suit and switch over to the Kanto-Denshi deflection and focus yokes, which would have required redesign or modification of the HDM, VDM, and focus/FGM boards.

So they stuck with the Thomson magnetics, which were apparently optimized for use only with the decidedly "different" Thomson CRTs, and NOT optimized for the MEC tubes.

To all appearances, since EVERY other CRT manufacturer using MEC tubes also used K-D focus and deflection yokes, it would seem that in fact the K-D yokes have always been the optimal choice for MEC tubes IF your drive circuits are engineered to work with them.

So, the Marquee has been using poorly matched magnetics for something like 20 years now. And we KNOW that the Thomson focus yokes are a major weakness.


But you can't just put in the K-D focus yoke and use the original Thomson deflection yoke and expect it all to work perfectly.

The reason is physical: The Thomson focus and deflection yokes are engineered to work as a system, on a Thomson CRT,
and conversely, the K-D focus and deflection yokes are ALSO designed to work as a SYSTEM, on an MEC CRT.

Simply swapping around the focus yokes forces the K-D focus yoke to be almost an inch farther back on the tube neck than it was designed to be, because the K-D deflection yoke is close to an inch shorter, and thus, when you pair up a K-D deflection yoke with a K-D focus yoke, the magnetics are where they should be on the tube neck.

But they're not going to be driven correctly by stock Marquee drive circuits. The inductance values are way off target, relative to what the Marquee electronics are expecting.


So, to optimize not only performance with LUG tubes, but with ANY MEC/Panasonic/Lexel/Clinton/Mikado CRT, certain things need to be changed.

We want to change over the projector to run with K-D focus AND DEFLECTION yokes.

This will require a significant rewiring effort on the deflection yoke as while it has all the same corresponding coils as the Thomson
deflection yoke, the connections between them are different. And you have to change out the wiring harnesses, too.

Once that is done, you have to dig out the Marquee service manual, a calculator, and possibly an AC electronics textbook, and
figure out what component values (capacitors) need to be changed on the HDM, VDM, and FGM in order to restore the series resonance of each circuit.

And you have to alter the capacitor values in EACH H-scan band range, not just one, unless you neve want the yokes to work right except in a single scan frequency range.

I wish I'd explored this in more detail years ago, when it would have been easier to come up with more candidate focus and deflection yokes.


But I will give one word of advice: If you encounter a projector with MEC tubes in it, regardless of manufacture, and if it is being
scrapped, you might want to grab ALL of the magnetics off the tubes. That is, if you want your Marquee to focus better,
particularly with LUG tubes.

[cmjohnson]

I'm more convinced than ever that the Thomson focus yokes were designed to be cheap to make, and CHEAP they ARE.

Their design incorporates six low cost cylindrical magnets and I have found from experience that you can occasionally run across
one which has imbalanced strength between the six internal magnets, which skews the alignment of the static magnetic field and if that's too far out of spec, you're never, ever going to get the raster position to be stable with changes in focus.


I've come to the conclusion that I'm probably going to have to see if the guys at VDC will agree to recalibrate a bunch of my
stock of focus yokes on their calibration fixture. Obviously some of these have been knocked around and it's a time consuming pain in the butt to swap them out and figure out which ones are good and which ones need remagnetization and recalibration.


But then again, I'm getting really good at making the flare, astig, and triangularity adjustments now, too. I'm getting lots of practice.