For definitions of air coupling (AC),
liquid coupling (LC), or c-element, see this
page. Many air coupled (AC) projectors were originally manufactured with clear
glycol in the red and green tubes in order to increase the overall light output of the
projector. Some home theater enthusiasts choose to replace the clear
glycol with tinted glycol in order to achieve more accurate colours (i.e. more
accurate SMPTE-C primaries). This is referred to as colour filtering.
How
much of a difference this actually makes to the projected image is hotly
disputed on many online forums with some saying the difference is huge and
others indicating that it's not worth the hassle. Proponents of colour filtering
will tell you that without colour filtering reds tend to look orange and greens
tend to look yellow. Regardless of the projector in question, only the red
and green are ever colour filtered. Blue is never colour filtered. Below is a
screenshot with the red tube displaying an image. The left half of the
image is un-tinted while the right side shows the effect of tinting.
Red tube output: No colour filtering on the left, colour
filtering on the right
(Thanks to cmjohnson [CJ] for the example photo) Air-coupled (AC) projectors achieve colour filtering by using
tinted glycol in the coolant chamber in front of the CRT face (ex: Sony
125x/127x, Barco 800) or by using a tinted element with the lenses themselves
(ex: the HD-144 lenses on a NEC PG or XG). Many AC projectors do not use
colour filtering at all.
Every manufacturer is different.
Some, such as Barco, tinted their earlier models such as the 800 and 801, but
then stopped tinting in later models such as the 808 and 1208 in order to
increase light output.
Colour filtering of liquid coupled (LC)
projectors can only be achieved by replacing the clear red and green c-elements
with tinted ones.
Sony 1272 air-coupled projector with tinted glycol
Barco 808 air-coupled projector with clear glycol This article
deals only with the changing of clear glycol for tinted glycol in the red and
blue tubes. Changing of clear c-elements to tinted c-elements is dealt with in
other articles on this website. Below is the procedure that
you can use if you want to tint your own glycol. This is considered a
very advanced procedure as it requires you to completely remove the tube(s) from
the projector. While this procedure was originally written for using a Barco
808 as an example, it can be easily adopted for other projectors with clear
glycol if needed.
The following procedure and pictures were graciously provided by
Bjørn Hegelstad of Norway. His web site can be found at:
http://www.crtht.com. Bjørn offers home
theater installations, CRT sales, CRT modifications, and gray scale calibrations.
Warning!
I can’t guarantee any of this, this
is only for other HT-enthusiasts that like to test and try new things.
I have only tried this on the
BarcoGraphics 808s tubes, and other tubes can be different in construction so
this procedure may not work on them.
You do this entirely at your own
risk.
Background information and testing: This whole project got started because of
Rosco color filters (essentially coloured see-through plastic sheets) and what
they did for the colors on CRT projectors without color filtered lenses/glycol.
Rosco filters got the colours right but at a cost: The colors were beautiful but
the filters produced reflections and ruined the black level.
That was when I started on tinting glycol. Because I have a BG808s that is
color filtered with the glycol from a BG801s, I thought there had to be a way to
get coloured glycol.
But after a lot of mailing around, I still had not found out where to get
hold of the red and green glycol.
I then got some interesting suggestions from other enthusiasts: First I tried
with ink and it looked great but it was entirely water based so I didn't think
that would be clean enough for the glycol in a CRT projector.
Then candy dye was suggested and I found out that it was glycol based, so I
thought that would be better than the water based ink. So I started testing and
finding out how to mix it and get the right color density. After a lot of
testing I found out that the candy dye color density didn't last very long.
Then I got back to inks and I found out that it was more correct; with
magenta for the red tube and cyan for the green tube. That's where I am now and
the only thing left is to test if the ink/glycol combination lasts as long as
the original coloured glycol.
Fast forward a few days...
The colors are holding their density so far. This is a much better way to do
the color filtering than the Rosco filters, because there are no reflections and
there is less light loss.
I am going to take a measuring every 50 hours of the color density of the
coloured glycol to see if it is keeping the right color for long term use. I have
supplied this to a few BG808s users for testing as well.
The coloured glycol I have mixed gives the same coloring as the BG801s
original coloured glycol. I can't give any guaranties how long it will last, but
it gives the most beautiful colors I have ever seen on the BG808s.
Fast forward a few months...
I measured the BG808s projectors with ink coloured glycol and they are all
stable. They have been used from 100 to 220 hours since they where color
filtered with ink in the glycol. That means that the project has been a success
this far, and this is the cheapest way to get beautiful colors on air coupled Barco
projectors.
I am also warning people about the early tests with the candy dye, as it did
not work at all as the green candy dye changed color after a short while and the
measurements where much worse than with out the dye.
If anyone has used candy dye you should change it to ink based or clear
glycol.
For results of the tests, see the CIE chart and measuring on the very last
page of this procedure.
Update: One user of this tinted ink (Nicholas) has indicated that for him
the ink-tinted glycol had faded over a period of a couple of months just sitting
in a container in his closet (unused). Caveat Emptor. Others have
had absolutely no problems over 7+ months (forum member 'secstate').
Another option that some users are adopting: Instead of
tinting clear glycol, some users are using the tinted glycol from worn tubes
in older projectors that had tinted such as the Barco 800 or the Sony 125x/127x.
Older projectors such as these with worn tubes can be had for next to nothing,
so it's a viable option assuming that the glycol's still usable (not cloudy).
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