8mm Forum: Bell & Howell 644 With HID Lamp

This is topic Bell & Howell 644 With HID Lamp in forum 16mm Forum at 8mm Forum.

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Posted by Maurice Leakey (Member # 916) on November 07, 2013, 10:02 AM:

Members may be interested in a conversion which has been carried out to my Bell & Howell 644 to use the Xenpow 150watt 95volt lamp.
http://www.decks.co.uk/products/Lighting_Bulbs/Xenpow/lamp_hid_150?gclid=CO6a076B07oCFVMRtAodv1IAWQ#.Unu0jpXuPIU
Items required for the conversion were the Lamp, Ballast, Electric Fan, Lamp Switch, Connection Block, Lamp Securing Spring.

Items removed from the projector were the Lamp Holder and Fan Assembly.

The existing condenser assembly was modified to hold the new lamp (secured by a spring), small cut-out made on panel behind drive belt for clearance of side of lamp, on/off lamp switch fitted on amplifier side control panel, gauze safety shutter replaced with solid dowser, main control switch rewired to operate dowser, electric fan wired permanently to mains input.

The new lamp has a life of 1000 hours and with its truly white light gives films a new life on the screen

Posted by Robert Crewdson (Member # 3790) on November 09, 2013, 04:12 AM:

Very expensive lamp, I am sure they could be offered cheaper than that. When my Euro Millions numbers come up I'll think about a conversion.

Posted by Maurice Leakey (Member # 916) on November 09, 2013, 06:19 AM:

A bright white light which costs £0.065 per hour cannot in any way be considered as very expensive.

Posted by Robert Crewdson (Member # 3790) on November 09, 2013, 09:01 AM:

When you see quartz bulbs used in domestic lighting they are as low as £3 for a pack of three, they look identical to projector bulbs. If you are unlucky enough to have a faulty bulb or one that goes prematurely then you have to fork out £65 for another.

Posted by Robert Crewdson (Member # 3790) on November 10, 2013, 04:25 AM:

Let us hope you don't have a repeat of the problem you had with it's brother, the 652 and the exploding lamp.

Posted by Maurice Leakey (Member # 916) on November 11, 2013, 03:08 AM:

quote:
When you see quartz bulbs used in domestic lighting they are as low as £3 for a pack of three, they look identical to projector bulbs

Members may not be aware that the Xenpow HID 150 lamp used in my 644 conversion bears no relationship to other lamps which may look somewhat similar. Look at the picture of the lamp and you will see why.

HID lamps require over 20,000 volts to ignite the lamp and then 95 volts to keep them running. A ballast is a necessary part of the system. Apart from turning it on it also regulates the voltage.

The power-up is in three parts. First comes the ignition when a high voltage pulse is used to produce a spark which ionizes the xenon gas, creating a tunnel of current between the tungsten electrodes. After this comes the initial phase when the temperature in the bulb capsule rises rapidly, the metallic salts vaporise and the resistance between the electrodes fails. The ballast comes into function and automatically switches to continuous operation, when all the metal salts are in vapour phase, the arc of the light has achieved a stable shape and the luminous efficacy has attained its nominal value. Being supplied with stable electrical power by the ballast, the arc will not flutter.

From switch on to normal brilliance takes about two minutes. The lamp remains on during the whole of the show and is only turned off at the end. A dowser is employed to cut off the light when the projector is in stand-by or lacing mode. A lamp must be completely cold when first switched on, never when hot or even warm.

Such a lamp cannot be compared with any conventional projection lamp or similar.

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