[Shodan]

Hello,

i currently own a Sharp 9000 with a Stewart Firehawk and I want to move on to a CRT. Since I have no experience at all with CRTs I need some very basic information and advice:


- Which companys produce new CRTs (like Barco) and which companys are only modifying them (like Runco)?

- Would a Barco Cine 6 produce a better picture than my Sharp?

- I would need some sort of "CRT technical guide for dummies" to understand how exactly a CRT produces the picture and what are the most important technical details to look at when comparing two PJs.

- What kind of PJ (7", 8" or 9") would I need for a 110" diagonal 16:9 picture (Stewart Studiotek 1.3)


I would be very happy about answers, or some useful links that could help. Sorry for misspellings, but english is not my first language.


Thank you all,

George

 

[Tim in Phoenix]

Sir


Welcome to AVS Forum!


CRT is short for "cathode ray tube"; the technology is similar for direct view tubes as well as projection types. Most CRTs employ a funnel-shaped glass envelope containing an electron-emitting mechanism or "gun", and a glass plate coated with light-emitting phosphor compounds. After assembly, the tube's air is pumped out until a vacuum results. The cathode of the gun is heated by its' filament, or heater, to enable electrons to easily boil off. The tube face is charged from a power supply with 30-40,000 volts, and some other bias voltages cause a stream of electrons (the beam) to fire from the gun end and strike the phosphor. The incoming video signal is amplified from 0.7 volts at the displays' input to 140 volts or more to drive the cathode. Less cathode voltage allows for more beam current, a higher voltage shuts it off, so the cathode drive signal waveform is inverse relative to the input source signal waveform. A tube with a blown drive circuit but other voltages intact runs wide open with retrace lines visible and would soon shatter from overheating the tube face if allowed to. The modulated cathode signal represents pixels of the source image; this beam can be steered about the tube face by magnetism; the pixels are distributed across the tube face by signals fed to magnetic windings of the sweep yoke; a vertical sweep signal of 50 or 60hz for typical PAL or NTSC video, up to 180hz for some computer signals. The horizontal yoke windings are driven much faster; a scan line may be drawn 15,750 times per second (15.7khz) for normal NTSC video, 31.5khz for a line-doubled or de-interlaced NTSC feed, 33khz for HDTV at 1080i, 48khz for line-tripled, 63khz for line-quadrupled, and even higher horizontal rates for computer graphics and some HTPC outputs. Other magnets or magnetic windings mounted on the tube neck assist in controlling focus, also known as spot size; stigmation correction, or dot shape; dot flare; and convergence correction. In a projector, the three images from each tube are fired at the screen from angles but need to be square at the screen and matched to each other; the convergence circuitry distorts the image (raster) shape on the tube face so as to be square and linear and matching the other colors at the screen. Some geometry functions such as linearity, bow and pincushion are executed through the convergence circuits. The image drawn on each tube face is delivered to the screen surface through a lens assembly, and there you have your typical three-tube video projector. CRTs may lack the big lumen output of lamp-driven systems, but excel in pixel-free reproduction and accurate black and deep grays. Better CRT systems have eight or nine inch tubes, liquid-coupled optics for superior contrast ratio, and can deliver a truly involving filmic experience on your living room wall.

 

[JoyMan]

Hi Shodan,


I would suggest the 9" for a better feature and brightness, and check out www.vdcdisplaysystems.com as the handle and develop the well-known Marquee (from Electrohome). They are available in 2-pieces now! It is a good idea if you do not want to 'see' something big on the ceiling.

And they've just increased the bandwidth of the Marquee !

FYI, the Madrigal MP-9 and Vidikron Vision One are using the Marquee 9500LC Ultra engine. Runco also has now, with the GT-17 lens.


Ciao.

 

[Shodan]

Thank you guys for the answers!

About the screen size: Whats the maximum diagonal you would do with a 7" (Barco Cine 7 or Runco 940)


George

 

[cpurvis]

You can calculate exactly how big you can go with a given projector by using the formula discussed here:

http://www.avsforum.com/avs-vb/showt...ht=footlambert


correct me if I'm wrong but you ideally want something like 12 or 13 footlamberts / sq foot right? (help me here, experts).


If you don't want to do the math most people seem to say a screen width of 80 inches is about the biggest you want to go with any single CRT. That would be a 91 inch diagonal 16:9 screen or a 100 inch diagonal 4:3 screen.

 

[Art Sonneborn]

George,

Unfortunately it appears that we are getting near the end of the road for CRT. I think on AVS forums it is common knowledge that CRTs provide superior picture quality overall, including blacks to the floor and a nearly liquid image. The down side is maintenance and the limited screen size possible due to the lower light output compared to bulb type projectors. If you can find the true ANSI lumen light output on the projector in question then use the formula: ANSI lumens x screen gain/ screen area in square feet = foot lamberts. You should shoot for at least 10 foot lamberts to get a picture that will have punch or not look flat. Therefore the screen gain and PJ ANSI lumens will determine the maximum screen size.

Art

 

[OzRoscoe]

Quote:

Originally posted by Art Sonneborn If you can find the true ANSI lumen light output on the projector in question then use the formula: ANSI lumens x screen gain/ screen area in square feet = foot lamberts. You should shoot for at least 10 foot lamberts to get a picture that will have punch or not look flat. Therefore the screen gain and PJ ANSI lumens will determine the maximum screen size. Art

Thanks Art! I am considering the Sony 1272q. Just wondering if anyone can tell me what the ANSI Lumens would be (Projectorspecs tells me 700 Peak Lumens). Also, using a standard painted wall (say flat white/grey) what gain value could be used?


Thanks in advance,


Roscoe

 

[Shodan]

Right now I use a 100" with my Sharp, and I thought a bigger picture like 110" couldn't hurt. But since I now so little about CRT I did not consider the lesser light output :-(

If 90" is perfect, would 100" with a Cine6 in a completely dark room with a good source (Proceed PMDT with PVP) still do it? Or should I under no circumstances go bigger than 90" (16:9)


I am pretty sure now, that I will take a Barco Cine 6. Just to experiment a little and see if I like it. And in 6-8 months or so when I now a little more about it when I tried some things like different scalers and resolutions, I would probably sell it and go for a Cine 7 or Runco 940 (still not sure if the Runco is worth the extra money).


Once again, I must thank you all for the great help, I did not expect so much response!

 

[CH Yeow]

Shodan,


The Cine 6 can only take line doubling. The Cine 7 is only good with up to tripling but on a computer resolution at 1024X768 is best. beyond that the 7" guns cannot give a very sharp image.


Marquees 8" guns produces very sharp and beautiful colours and an old set with new tubes will outperform a new 7" CRT.


Tim as a huge knowledge on Marquees inside out.


As for brightness, go for 8" and beyond. After fully set up by an expert, you will not go back to the digital projectors as long as they are still "very close to CRT picture quality". IMHO.


CH Yeow

 

[Shodan]

Thank you guys for the help! I have decide to buy a Cine 7 because of the limited availability of other projectors in my country (Austria). Now I need a video processor, but I will move my questions to that forum.


George