For definitions of c-element, liquid coupling (LC), or air coupling (AC),
Many liquid coupled (LC) projectors were originally manufactured with clear
red and green c-elements in order to increase the overall light output of the
projector as the original use for many of these projectors was not for home
theater. Light output was more important than colour accuracy. Home theater enthusiasts choose to replace clear
c-elements with tinted ones in order to achieve more accurate colours (i.e. more
accurate SMPTE-C primaries). This is referred to as colour filtering.
Without colour filtering it is not impossible to achieve correct primary
colours on a CRT projector: Reds tend to look orange and greens
tend to look yellow. As explained in our
Color Calibration for Dummies guide, ensuring that the raw or "primary"
colours used to create all colours are correct is critical to both greyscale and
Think of painting with a brush: Greyscale calibration ensures that the proper
amounts of paint are mixed together to get the colours we need, while colour
calibration ensures that we have the right base colours to mix in the first
place. Using tinted c-element ensures that we start with the right base colours.
For example: If your bucket of red paint isn't perfectly "pure" red, no matter
how you mix in the other primary colours you'll never you'll never be able to
get that red any more correct.
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 and looks orange while the right side shows the effect of tinting
and has a deeper red hue.
Red tube output: No colour filtering on the left, colour
filtering on the right
(Thanks to cmjohnson [CJ] for the example photo)
Every manufacturer is different.
In the case of the Marquee 9500LC the c-element on the green tube of is already
tinted green. Only the red needs replacing. In the case of the Barco
1209s, both the red and green c-elements are clear so both need replacing.
Some LC coupled projectors already have both c-elements tinted. The Sony
G70 and the Zenith 1200 are two examples.
Note: Colour filtering of LC
projectors can only be achieved by replacing the clear red and green c-elements
with tinted ones. 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 an NEC PG or XG). Many AC projectors do not use
colour filtering at all.
Sony 1272 air-coupled projector with tinted glycol
Barco 808 air-coupled projector with clear glycol
however, deals only with changing of c-elements for Marquee LC projectors.
Tinting of air-coupled projectors will be dealt with a future article.
Below is the procedure that
you can use if you want to do the c-element change yourself. This is considered a
very advanced procedure as it requires you to completely remove the tube(s) from
While this procedure was originally written for the Electrohome
Marquee 9500LC, it can be adopted for other projectors with clear
c-elements if needed.
Tinted c-elements are available from both
VDC and 3M.
The following procedure and pictures were graciously provided by
forum member HK-Steve.
• Allen or Hex drivers Keys
• Flat Blade Screwdriver
• Towels or Paper Towel
• Container for the Glycol
• 60ml or larger Syringe
• Small diameter tubing or heatshrink tubing
• RTV Silicon
1. Well you already know how to remove the tubes from your Marquee Chassis, so I
won’t go through the procedure, so with your tube removed you are ready to go.
2. Remove the Hex Screw in the top of the LC assembly; be careful when you take
the screw out, there could be some pressure and glycol with spurt out. Put some
paper towel over the top to absorb any glycol.
A hint from forum member
erikjohn: In order to prevent glycol from squirting out remove the top and
bottom pivot pieces and flapping adjustment screw. This allows you to release
any pressure that was squeezing the bellows and ensures that you will not get a
big squirt which can make a mess and get to the magnetics and raise hell.
3. Remove the 2nd Hex Screw; it will let air in as you take the glycol out.