8mm Forum: Bell & Howell LED Lamp Conversion

This is topic Bell & Howell LED Lamp Conversion in forum 16mm Forum at 8mm Forum.

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Posted by Maurice Leakey (Member # 916) on August 03, 2015, 02:45 AM:

Whilst delivering projectors for repair and collecting those having been serviced by Kevin Brown of Nottingham he showed me two Bell and Howell lamp conversions.

A 30 watt LED lamp had been fitted into a model 643 and apparently gives quite an adequate illumination on a 4ft screen.

The basis of the conversion was the outdoor COB 30 watt LED flood-lamp. Only the lamp and its power supply were used.

The 642 and its similar brothers are suitable, these models use the 1000 watt reflector lamp (A1/207) and have a separate condenser lens assembly. The latter is retained in the conversion.

The 30 watt lamp was chosen as it is about the same size as the condenser assembly. It is mounted on a suitable bracket approximately 10mm behind the condenser. No mirror is required.

It was most important that an adequate heat-sink was fabricated, as if insufficient for the job it could hasten an early end of the LED's life.

The other interesting conversion was a Bell & Howell 666 for which lamps are now very difficult to obtain. The complete power supply unit on which the projector stands was dispensed with and a new HID 150 lamp installed. This requires a ballast so space is made available by removing the existing large fan and fitting a much smaller one. (Much less heat now to shift.)

I can vouch for the HID 150 conversion as Kevin has modified my Bell & Howell 644 to use this replacement lamp and I can say it's a great performer.

Posted by Terry Sills (Member # 3309) on August 03, 2015, 12:51 PM:

Great news Maurice. Lets hope that this is the beginning of a much wider conversion program that encompasses other gauges. What I do not understand is the exact purpose of condenser lenses. More modern projectors don't use them so why were they needed on some older machines?

Posted by Paul Mason (Member # 4015) on August 03, 2015, 01:40 PM:

Terry,
Condensers were needed before the arrival of lamps with parabolic mirror reflectors to concentrate the spreading light rays of the lamp filament. Any projector lamp or led without a mirror will need one.
Maurice,
That is very interesting. I think a slightly more powerful led than 30W say enough for 6-7 ft would be ideal for 16mm.

Posted by Brian Fretwell (Member # 4302) on August 03, 2015, 04:00 PM:

The fact that those lamps were also mains voltage and had large filaments is one reason for the condenser lens and separate reflector in some.
I think the area of the folded filament would be a good match for the 30w LED chip. I was considering trying this myself with an old B&H 642 I salvaged when it was being thrown out. I have never got round to fixing the valve amp that died during testing but I had a couple of silent films I ran on it. My attempt will be when I get around to it I'm afraid.

Posted by Maurice Leakey (Member # 916) on August 04, 2015, 02:25 AM:

A higher wattage LED is also physically larger in its overall size, and as such, the larger expanse of light will not all go through the condenser lenses assembly.
There is no advantage in having an LED panel larger than the condenser.

Posted by Paul Mason (Member # 4015) on August 04, 2015, 02:58 AM:

I take the point about the limit to the size of LED. I expect that LED sizes for a given power will reduce in time.

Posted by Steve Carter (Member # 4821) on August 04, 2015, 05:40 AM:

Maurice is this the type of lamp you now have fitted HID 150w...
HID 150w lamp

Posted by Maurice Leakey (Member # 916) on August 04, 2015, 09:26 AM:

Yes, it is.

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