CurtPalme.com Home Theater Forum

[tschaeikaei]

Hey, I left the BG400 standing in my cellar an bought a wonderful Graphics 801s from barclay66.
Yes, it was definitely worth traveling 460km one way to Munich. Thanks again barclay66 for that nice weekend.
The 801s is not in original state, but with Liquid coupled tubes and the belonging HD18 lenses.
Works just fine. Sure, I've done everything. I adjusted everything, mechanical and electrical, yes astig too.
And it is now good enough to read 10p font on 1280*720p on a 113" diameter screen.
The only wish I have now, is improving the focusing. It already is good for an ES model,
but could be better.

So I searched the Internet for modding techniques. I also talked to barclay66.
My idea is to simply add a focusing coil on the neck of the tube. Barclay told me that EM tubes
are longer the Es tubes, to place the focus coil on them.
I hardly found pictures, but the focus coil usually seems about 2 or 3" long.
I understand that a shorter coil must be difficult to tweak, because the electron beam could be focussed to much,
that it crosses itself and defocusses more than without the additional coil.

I would like to test it tough. As I understand it, the focus coil is driven with DC voltage.
That emits an negative field in the center of the tube, so that the electron beam is pressed together,
wich results in a finer beam. Shure it must be difficult, and I don't think it would produce a picture like
a bought EM tube, but is it worth trying? Is any improvement expectable?



Has anyone tried this before? Does anyone have literature on this?

Please don't think I am meaning to reinvent EM focusing or something. I'd just like to know if an ES tube is improvable.

Thanks for any idea,
regards
Julian

[gjaky]

I think the Sony 1292 had a dual focus system (ES and EM). In theory it could work. There are two major problems with the ES technology:
1.) the focus setting affects the whole tubeface at the same time, which means you most likely get good focus only in the center.
2.) the tubes loosing focus with usage.
Your idea could cure only the second problem if it works. A real EM system however can eliminate the first problem too, and that is the big thing!

Before you dig yourself in this project I suggest you to check how is the tube focus related to electronic bandwidth. The specification of the barco 801 saying 75MHz bandwidth, which is barely enough for even 720P.

Put up a resolution test pattern, where 1 line on : 1 line off vertical and horizontal patterns are easily comparable. Horizontal lines are not affected by electronic bandwidth, only by spot size (ie. focus) and dot shape, while vertical line thickness is limited by the spot size and with the electronic bandwidth too. If your horizontal line pattern looking better than the vertical line pattern, you don't need to improve the focus further, if both patterns looking equally you may get an overall sharper picture.

[km987654]

[RaWsHaRk]

with the tubes it has it wont get better no matter what you do. if its not enough for you, get a 808,1208 or a marquee,...

[tschaeikaei]

Sorry for not replying for such a long time.
I had some other things to do and could not concentrate on the projector.
What I discovered is that if you adjust electrical focus with high contrast and brightness settings,
it gives (even in dark scenes) a much better picture than if I adjust focus using low contrast/brightness
settings while adjusting.
That "trick" results in an about 60% better picture. It's nearly perfect for me now.
The only thing is, when I adjust those settings and watch a movie, it drifts.
I have to readjust from time to time. Sure, the convergence settings are drifting too,
that be be a result of my input signal: 1280*720p from my PC.
Picture wide @99% and picture height at 12% or so.
I heard it drifts the fewest if you set everything to around 50%. Should I try a 1280*1024p setting?
Regards,
Julian

[Curt Palme]

Your convergence drift is most likely due to aging capacitors. Kal recapped his power supply years ago, and said that the set ended up much more stable. If you know how to solder, you might try changing the capacitors on the power supply and whatever ones you can find on the convergence board.

[Curt Palme]

Your convergence drift is most likely due to aging capacitors. Kal recapped his power supply years ago, and said that the set ended up much more stable. If you know how to solder, you might try changing the capacitors on the power supply and whatever ones you can find on the convergence board.

[tschaeikaei]

"Recapping" seems a good idea to me too.
Yes I am able to hold a soldering iron, but there's a heck of caps in that machine.
If I buy every single cap, thats a real investment.
Ok, it is a hobby and maybe worth it.

The other idea is to somehow "stable" the electrical focus board.
The are only resistors in that unit, and they get warm when the machine is running.
Cool down if I use the pause- button, get warm again. Always depending on the picture.
The more white in the picture, the more they warm up.

Simple test: I took a 56kOhm resistor out and a Ohmmeter. 56,0kOhm at room temperature.
I heated it up (sure much more than in the projector) and the Ohmmeter said 49kOhm at about 200°C
wich is 390°F. That was a cole film resistor.

Metal film resistor: room temperature: 91,6kOhm, 200°C/390°F 90,9KOhm .
That is much better.

Looking in the manual, I found nothing on wich type of resistors are in the "focus black box",
the mold thing with the focus pots.

Did anyone here ever open such a box?

I could even try an additional cooling fan, but the box is made of plastic, a material that does not
conduct heat well.


Regards, Julian