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Old 9th Jun 2022, 2:52 pm   #1
EF80TVVALVE
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Default GB Equipments Gebescope L516 16mm Sound Projector

Hi all,

I've just picked up one of these models of projector, Im hoping some forum members have had experience with them and may be able to help. This particular example is missing the resistive dropper and speaker, the dropper isn't much of an issue as I'll be using a 110v transformer instead, in fact I'd much prefer this over the dropper anyhow.

The main issue I'm facing is the missing speaker unit. From the little information and photos I have found it seems as though part of the amplifier circuit is built within the speaker unit itself to save on space inside the projector.

I wondered if any forum members can help with identifying exactly what parts of the circuit lay within the speaker cabinet, it certainly looks like the output TX and a choke are sitting in there, so possibly part of the DC power supply and output stage.

With the above in consideration, I may see what modifications can be made in order to fit a modern transistor amplifier so that it is all contained within the projector unit. I not too comfortable with the idea of HT running through cables to the speaker unit which looks like a possibility with the current set up (until I know exactly what the circuit looks like).

Can anybody shed any light onto these projectors?
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Old 9th Jun 2022, 3:14 pm   #2
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Default Re: GB Equipments Gebescope L516 16mm Sound Projector

Originally an energised speaker and a brute force hum filter, later on PM speaker + choke.
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Old 9th Jun 2022, 3:21 pm   #3
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Default Re: GB Equipments Gebescope L516 16mm Sound Projector

Thanks for the clarification wd40addict, can I ask where the schematic is from? A full version would be a great help in returning it to working order and I can probably convince myself to keep the original amp too
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Old 9th Jun 2022, 3:32 pm   #4
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Default Re: GB Equipments Gebescope L516 16mm Sound Projector

As far as I can gather, the Gebescope was the standard projector used by the MoD. It's interesting in having no exciter lamp for the sound track, but 'borrowing' some light from the main projection lamp.

I came across this snippet of information https://www.villagehallcinemas.co.uk...m_9_gbl516.htm

Nice that the dropper resistor was known affectionately as 'The Toaster', particularly by army projectionists appreciative of its warmth.

I'd be intrigued to know more about the relationship between GB Equipments and GB Bell & Howell, the maker of my own vintage 16mm projectors.

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Old 9th Jun 2022, 3:45 pm   #5
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Default Re: GB Equipments Gebescope L516 16mm Sound Projector

Very complicated history of the companies associated with GB (Gaumont British).

I think they were only distributors for Bell Howell equipment but before that they took over Kalee who probably were the producers of the L516 proejctor, they made superb cine,a projectors , also mag film recorders and optical sound recorders using the Western Electric system.

BAF (British Acoustic Films) were apparently the parent company and my Gaumont Kalee model 564 Fluttermeter has a BAF label inside.

A fascinating topic, perhaps someone will research the subject and produce a tome someday.
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Old 9th Jun 2022, 6:47 pm   #6
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Default Re: GB Equipments Gebescope L516 16mm Sound Projector

Quote:
Originally Posted by Hartley118 View Post
As far as I can gather, the Gebescope was the standard projector used by the MoD. It's interesting in having no exciter lamp for the sound track, but 'borrowing' some light from the main projection lamp.

Quote:
Originally Posted by wd40addict View Post
Originally an energised speaker and a brute force hum filter, later on PM speaker + choke.
Yes. The two are connected! Running the projector on AC, the light from the projector lamp has optical ripple on it, which gives rise to hum. This is allowed to go right through the amplifier, and a series LC network shunts it out in the loudspeaker cabinet.
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Old 9th Jun 2022, 7:05 pm   #7
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Default Re: GB Equipments Gebescope L516 16mm Sound Projector

Thanks for the replies so far, I believe this one came from the Air Ministry by the AM stamp on it. Researching more online I found an example where somebody has made a box with a transformer for the lamp and the speaker supply parts in with a jack socket to plug a conventional speaker into, I think this would be the most suitable route to follow. I'm interested to see how this one performs, I've had a bell and Howell 601, I have an Ampro New-Educational currently and it seems this one sits somewhere between the two.
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Old 9th Jun 2022, 9:26 pm   #8
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Default Re: GB Equipments Gebescope L516 16mm Sound Projector

The company history is very complicated: GB, Rank, BAF, TTH, Kalee, BOPE...

GB brought out a new range of 16mm projectors in 1938, the top model used a B&H picture head, the others were home grown designs. The L16 model morphed into the L516 when a 500W lamp replaced the original 200W and became the mainstay of the UK services in WW2.

After the war there was a big demand for projectors and this time GB built entire B&H machines under licence hence 'GB-Bell & Howell'. They were joined by Ampro and Victor all building US designs in England. The top 100% British machine was the BTH. It's tempting to wonder if the designer of the L516 was also behind the short-lived Burville with its curved gate.

As yours is a military unit it probably doesn't have the still picture clutch. My money's on the Ampro being the better machine, but I'm biased as I have a New Educational, but have never finished the rebuild of my L516.

Amplifier circuit attached.
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Old 9th Jun 2022, 11:12 pm   #9
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Default Re: GB Equipments Gebescope L516 16mm Sound Projector

I seem to recall that the (weekly) magazine Amateur Cine World or its (monthly) relaunch as Movie Maker, published several articles on this projector in the 1960's. I don't think I still have the relevant issues.
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Old 9th Jun 2022, 11:19 pm   #10
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Default Re: GB Equipments Gebescope L516 16mm Sound Projector

Yes, in the 50s it was a very popular surplus buy. Mine was probably one of these as extra, more modern, suppression caps had been fitted.
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Old 10th Jun 2022, 2:32 pm   #11
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Default Re: GB Equipments Gebescope L516 16mm Sound Projector

Thanks for the attached schematic wd40addict. I think the Ampro NE is a good all-rounder, for a 16mm sound projector it is very compact, plus 240v operation does away with a bulky mains transformer. I picked this L516 up more to serve my own curiosities as its a model I've never encountered.

Can anyone supply any information for the specs of the chokes? Seeing as these form a hum filter then I suppose I'd better find some replacements for them.
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Old 10th Jun 2022, 4:00 pm   #12
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Default Re: GB Equipments Gebescope L516 16mm Sound Projector

ISTR there were several capacitors on a tag board, one end floating, so that shorting links could be soldered on to tune the filter - to cater for slight inductance variations and supply frequency.

If you could find the capacitor values and take the mid-range, then calculating the inductance is a simple matter (bear in mind of course, that you want to tune for 100Hz for 50Hz mains, because that's the optical ripple frequency).
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Old 10th Jun 2022, 4:39 pm   #13
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Default Re: GB Equipments Gebescope L516 16mm Sound Projector

Both 30H according to the speaker snippet I posted up thread.
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Old 11th Jun 2022, 2:13 pm   #14
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Default Re: GB Equipments Gebescope L516 16mm Sound Projector

how I missed that the first time around I don't know! I even remembered the capacitor values next to it. I'll wait to complete some work on the projector first and then I'll sort out the chokes, a quick search online throws a few up so hopefully they can be easily sourced.
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Old 17th Sep 2022, 3:12 pm   #15
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Default Re: GB Equipments Gebescope L516 16mm Sound Projector

Hi all
Well after a few months of not doing very much at all to this projector, I thought I'd start looking into solving the problems discussed prior. I've decided some modifications may be best in order to simplify the projector a bit. The first thought is to fit a new 240v halogen as the projection bulb, this will do away with the need for a resistance unit and still provide a nice bright picture. Secondly I'm planning on fitting a seperate exciter lamp, either a low voltage halogen or LED which will be fed from a DC supply. Doing this will simplify the amplifier circuit somewhat so I can hopefully do away with the filtering circuit that is needed to remove the 50hz hum from audio. It's likely that I will still need to fit an output transformer into the speaker unit when I make one up but it still solves a lot of my problems.

Any thoughts are welcome, I don't want to be removing the original amplifier and replacing it with something modern (which would make things even simpler) but I feel like the above would be an improvement and offer more convenient operation of the projector.
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Old 17th Sep 2022, 7:03 pm   #16
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Default Re: GB Equipments Gebescope L516 16mm Sound Projector

Should be ok as long as you keep the lamp <= 500W and its filament is of similar dimensions to the original so as much of its illumination as possible can be condensed through the gate.
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Old 17th Sep 2022, 7:30 pm   #17
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Default Re: GB Equipments Gebescope L516 16mm Sound Projector

Re the circuit in post #8.
What plugged into the "Transverter socket"

Presumably not one of these(!)Click image for larger version

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Old 17th Sep 2022, 8:47 pm   #18
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Default Re: GB Equipments Gebescope L516 16mm Sound Projector

The machine had to be able to run from all possible supplies: AC or DC, 200/250V, 100/110V. See attached.
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