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home>>Tech tips>>Tech tip #7
Preparing Marquee LC Tubes for Installation
Identifying VDC Rebuilt Versus New Tubes In a Marquee
Know your hardware! Here (see PIC 1) we have a VDC rebuilt tube in the foreground; the metallized lining, which conducts the anode voltage to the front of the electron gun, is a rust-brown color and identifies a tube as having come from VDC's Shreveport tube facility as recently as May 2003; VDC has just switched over to a black lining. The Matsushita tube in the rear has a dark gray liner. Both now incorporate Matsushita electron guns (see PIC 2); earlier VDC rebuilt tubes had guns with a funnel-shaped piece towards the rear of the gun; that gun design did not match well to the Marquee's Thomson yoke magnetics (see PIC 3) and often gave poor spot size. When moving the yokes from old tubes to new tubes, it is recommended to apply a strip of cloth tape (see PIC 4) to the tube glass to give the yoke clamps a better grip on the glass; the tape is usually found on tubes with factory-installed magnetics.

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Check The Pivot Pins Before Installing LC Tubes
Your Liquid-Coupled Marquee tube assemblies employ interlocking metal castings; the rear casting holds the tube face; the front casting holds the C-element lens, and the space in between tube face and lens holds over 20 ounces of glycol and water mixture; the fluid becomes the lens. The castings are held together by two steel pivot pins, one pin on each side. (see PIC 5) that enable the castings to tilt and scheimpflug top/bottom focus correction is then possible. Some new and some VDC rebuilt tubes were assembled with the pins merely pressed into position; such pins can vibrate loose during shipment of projectors or loose tubes bought as parts. If a pin gets loose or falls out (see PICs 6 & 7) then the tube face sits at an angle and proper optical focus cannot be achieved. If a pin falls out it can be tapped back in with careful use of a hammer. We recommend inspecting all tubes to see if the sides of the casting were crimped by a punch during assembly; if not, we advise doing this now (see PICs 8 & 9) as a simple precaution; the pins are most difficult to access in an assembled projector.

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Tim at E-Tech Systems Phoenix
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