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Changing a C-Element (Barco)

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For definitions of c-element, liquid coupling (LC), or air coupling (AC),  see this page.

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 Grayscale & 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 colour calibration.

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

This article however, deals only with changing of c-elements for Barco 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 the projector.

While this procedure was originally written for the Barco 1209s, 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 Bjørn Hegelstad of Norway.  His web site can be found at: Bjørn offers home theater installations, CRT sales, CRT modifications, and gray scale calibrations. 


Here is a little explanation of how I did the C-Element change.  

I have only done this is on a BarcoGraphics 1209s - other projectors maybe require other procedures.

The new tinted Red and Green C-Elements

1. First I removed the tubes from the projector.

The tube removed from the chassis

The chassis with all tubes removed

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