CurtPalme.com Home Theater Forum

[Lee2023]

Hi !!

So this is my problem !! I'm a bit out of ideas about this blue tube assembly focus problem


So I have managed to pickup a 9500LC projector with a not to badly burn phosphor blue tube, I know the projector have been dropped on the rear, deformed BNCs and plate, so I have installed this blue tube assembly in my projector and... focus was just bad, moving the focus coil forward a little improved a bit things but it's really not sharp

I swapped all the magnetics from my sharp but burned phosphor tube with not too much improvement...I have put all the magnetics back in my sharp tube, everything still sharp, now I have tried an other blue tube assy I have with an other kind of burned pattern with the ''good'' magnetics, and everything sharp !

So even with a nice phosphor the tube is not sharp because of it's age and the emitting zone on the cathode is bigger ? Or maybe the dropping of the projector have shifted something in the tube and the electronic focussing is kind of out of range ? Internals are really low mass so I'm not sure about this, or something I don't understand.. it's sad because the phosphor is really nice for it's number of hours, i'm really trying to save this tube assy !

I know the electronic focussing is working because i'm finding an optimum spot around 45 for the center, maybe the focussing is not ''strong'' enough ?

The ''new'' tube that is not focussing correctly is a revision C, LUG tube,

All the neck boards and tubes are revision A in my current projector, the other blue tube assy I have tested with some burns are also a Rev A coming from a ''rev A'' projector,


Also this Rev C tube is becoming more blurry as I push the contrast higher,


Any help will be appreciated, feel free to ask any question you want !!

Thanks !

Lee

[barclay66]

Hi,
Has the neck board been modified in order to work with a LUG tube? This is required as the LUG has the G2 voltage at a different pin and an additional grid.

[Lee2023]

Hi !

All of my 3 blue tubes have the same part number P19LUG03BMB,

So my rev A neck boards are configured for this kind of tubes

Lee

[barclay66]

Check out this thread: https://www.curtpalme.com/forum_archived/viewtopic.php@t=40132.html

[Lee2023]

Mmm, good thread,

Ok so I think the operation point of the non focussing tube is not good, since my magnetic and optical foccusing is supposed to be ok

I will put this tube assy in my test chassis and will do some measurements and tests with G2 / brightness like in the thread, I'm reading on pictures tubes in a good reference book I have kept for years, electrostatic, magnetic focussing, number of grids, etc, so, I think something seems to be wrong with the crossover point !! This point is the convergence of electrons after the control grid G1 and before the accelerating grid G2, so changing the operation point via G2 and Brightness on G1 should do something, the out of range EM focussing could be explained by this crossover point also the fact that moving the focussing assembly have improved a bit focus, since the electron beam is wider, the time to converge them is also longer if you keep the same magnetic field, so they doesn't have time to converge since the expanding beam after this point arrive wider at G2 and at the input of the focussing coil.... maybe, anyway

I will try to find a diagram of this LUG tube, internal structure, datasheet

Now, I need time to work on this, I will post my results, thanks for the link !

Lee

[Lee2023]

Ok !

So with some motivation I have manage to put the ''non focussable'' tube in my test chassis, and to my surprise it was sharp ! And I was able to see scan lines, so I have compared my living room projector with some blue tube in it and he have very not that clear scan lines,

So I have decided to swap the focus board and the back heatsink with all the board between my test projector and my living room projector, putted back the non focussable tube in my living room projector and ,,,, now I have a very usable blue tube assembly !! Now everything is screwed a bit I need to realign everything, but the important thing now I have a not too bad projector !!

Also the resistance to the KH electrode pin 7 on the neck board is one meg so this is good, I don't know if the 4.7 meg ohms mod produce a sharper image, I have seen a thread about that, anyway i'm happy with what I have now vs the time I have to put in this

Thanks again, still I have learned more things on this system, need to practice pole magnet adjustment now and the focus coil adjustment, and realign everything,

Lee