8mm Forum: Apollo 16mm Sound Projector

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Posted by David Evans (Member # 482) on July 22, 2019, 01:20 AM:

I have just acquired one of these - the 1930s type that "broadcasts' its sound to any medium wave radio - the only projector to do that as far as I know. I have rebuilt its valve (tube) electronics and it is broadcasting nicely at about 420 metres on the medium AM waveband. There is , however, no sound picked up from the film. The is a sound drum like a Bell & Howell has - nice free-running drum on ball bearings. There is a screened lead connected from the amplifier input to somewhere in the vicinity of the sound drum, but I CANNOT find an exciter lamp or a photocell! Nowhere to put one, no vacant holes, boxes, cavities or anything. Therefore I'm hardly surprised t5hat it doesn't work...

Does anyone have one of these and can explain where the exciter lamp/photocell are located?

Thanks for any help.

David Evans

Posted by Maurice Leakey (Member # 916) on July 22, 2019, 10:37 AM:

David
I don't know this projector, but having looked at an eBay ad, I would assume the exciter lamp is housed at the bottom of the assembly which extends south-east from the sound drum, the optics being in the long section.
The PEC must be behind the sound drum.
https://www.eb ay.com/itm/VINTAGE-APOLLO-SOUND-16MM-PROJECTOR-WITH-VINTAGE-CASE-MORE-/192766301882?_trksid=p2047675.m43663.l10137&nordt=true&rt=nc&orig_cvip=true

Posted by David Evans (Member # 482) on July 23, 2019, 05:22 PM:

Maurice, thank you for your input. The link you included is to the one we bought on eBay. If you look at the left side of the projector, just below the sound drum is a curved raised part terminating in a screw cap at the bottom. The screw cap removes to allow access to a slide-out flat piece of paxolin with a pair of vertical brass flat strips and flat terminals to connect it inside the housing. I was trying to upload a picture of this, but it appears to be impossible. Clicking on the upload an image link takes one to a page of instructions and warnings, but there is no Submit button on that page!
This slide-out piece has its flat strips 5/8" (17mm) apart and they are joined together by a piece of wire that has been expertly and neatly spot-welded to the tips of the strips (not soft soldered). Withdrawing this turns of the main projection lamp, so I concluded that it must be a fuse. However, the curved portion of the casting above it is hollow and directed toward the sound drum. If this housing is intended for an exciter lamp rather than as just a fuse holder, this might explain things. As this device is directly in series with the main projection lamp (500W, or 5 amps at 100 volts) any such exciter lamp would be carrying the full 5 amps. As the power of exciter lamps in 16mm projectors is typically around 4 - 5 Watts, we need an exciter lamp of festoon shape, 5/8"long, with a connection at each end, and rated at about 1 Volt at 5 Amps. There are no optics in this hollow channel. Can you suggest anything suitable?

The PEC as you say, must be behind the sound drum. Again, I have a picture explaining the problem, but basically there is no access to it without extracting the heavy flywheel from the sound drum spindle - something I am reluctant to try.

Thanks for your help.

David Evans

Posted by Maurice Leakey (Member # 916) on July 24, 2019, 03:59 AM:

David
Delving into the insides of a projector is something I just can't do, so I can't give much advice. But I do think you should dismantle as much as you can to find out how it all works.
You seem to be aware of the technical aspects of a sound projector.
Remember that a PEC needs a working voltage of around 90 volts. As to exciter lamps, many years ago they were fed by AC and to stop the fluctuations and ripple being picked up on the sound track the exciter lamps had very thick filaments and operated at quite a few amps.
In later years they were fed with oscillated DC and the lamps and their filaments became much smaller.
You have an excellent project and I wish you luck with it, but I am not technically able to offer much assistance.

Posted by Kenneth Horan (Member # 3) on July 24, 2019, 03:35 PM:

There was no exciter lamp on these Apollo 16mm sound projectors. To keep costs down the manufacturer, Excel Movie Products of Chicago, used a short length of nickel-chromium wire for sound track excitation.

Posted by David Evans (Member # 482) on July 24, 2019, 07:00 PM:

Kenneth - that sounds like exactly what is there at the moment. I have not noticed it glowing though - how bright should it be? Thanks for your input.

Maurice - thanks for your input too. In an earlier life I was a professional R & D electronics engineer in the field of Military communications and have been repairing valve equipment for 50 or so years.

There is a potentiometer in the amplifier circuit that adjusts the DC on the PEC up to 100 volts.

I hope to get to the bottom of all this eventually!

Posted by Kenneth Horan (Member # 3) on July 25, 2019, 12:31 AM:

It has been a while since I have worked on an Apollo 16mm sound projector. I do not remember the nickel-chromium wire glowing. It emits infrared radiation which is invisible. That is why the Apollo could not reproduce sound from Cinecolor or blue-track Technicolor prints. The Apollo only worked with silver tracks.

Posted by Maurice Leakey (Member # 916) on July 25, 2019, 04:16 AM:

I see that its 1950 price was US $139.50. What a pity they scrimped on its details.
I've got a Debrie 16mm which has no separate exciter lamp. Its projection lamp is upside down and also shines on to the sound optics.
https://www.ebay.ie/itm/1950-small-Print-Ad-of-Apollo-16mm-Sound-Movie-Projector-/173668504710

Posted by David Evans (Member # 482) on July 25, 2019, 01:33 PM:

Gentlemen thank you both - the Debrie was a fine machine - an interesting way to illuminate the PEC! I have that ad - possibly from a mail order cat, not sure. Doesn't seem logical that they would use the IR source as a price cutting exercise - that was quite a lot of money in 1950!

Ken, the wire glows a dull red in operation. Infra red... Does that mean that the PEC is special? Maybe a TEC (thermo-electric cell)? Or do PECs respond to IR? I'm not quite sure what exactly the silver track is. Presumably black & white film, but will any B & W film work? The thing is obviously still not working, as I tried the time-honoured test of inserting a piece of thin card between the light (heat) source and the sound drum, and no change to the output.
I was wondering about putting a LED in the light/heat tube, without compromising the originality of course. It could be fed from the amp HT supply and would be well decoupled, so mains frequency should not affect things.

Thanks again both.

David

Posted by Maurice Leakey (Member # 916) on July 25, 2019, 01:42 PM:

A silver track will give a black and white sound track.
Some colour films do have a black & white track, but not all.
https://www.paulivester.com/films/filmstock/guide.htm

Posted by Kenneth Horan (Member # 3) on July 25, 2019, 10:45 PM:

The 16mm sound Apollo projector uses a special photo cell sensitive to infrared radiation. When this projector was introduced in 1948, the $129.50 selling price was very low for a 16mm sound projector. The Calvin Movie-Mite, the next cheapest 16mm sound projector, was almost 2½ times as much. Any standard 16mm sound print on black and white stock has a silver track. Color prints may have a dye or silver track. The Apollo would not play back a dye track very well, if at all.

The photo shows the parts for the Apollo sound pick-up.

This photo shows the Apollo with the 2000 foot adaptor.

Posted by David Evans (Member # 482) on August 14, 2019, 10:14 PM:

Hi Ken

Thank you for the pictures. What is the small device between the glow unit and the sensor?
I assume there is zero chance of getting an IR photocell, so will have a go fitting an LED sound exciter lamp and see what, if anything, happens.

Sorry not to have been back to you earlier, but the Forum was unavailable from here for a week or so recently. Seems OK again now.

Thanks for your input - all most interesting.

Regards.

Posted by Kenneth Horan (Member # 3) on August 15, 2019, 01:25 PM:

David Evans wrote: "What is the small device between the glow unit and the sensor?"

It is an optical tube to conduct the light. It works like today's fiber optics.

Posted by David Evans (Member # 482) on August 15, 2019, 01:53 PM:

OK - I think we do not have that. There is nothing in the metal tunnel, just the IR wire at the bottom and the heat-sensitive PEC (presumably - I haven't checked that out yet) at the top.

Regards

David

Posted by Kenneth Horan (Member # 3) on August 15, 2019, 02:48 PM:

The photos are representative of the first year of production, 1948. It's possible that later production units were modified and omitted this part.

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