Joinville 2
THE JOINVILLE SERIES
Page 2
Page 1 A Pax Sound Conversion
PATHE PM PROJECTOR - A WARNING
I have only recently (July 2018) gotten around to the point of live testing the PM as a projector (with its amp outside and powered separately). After only a few minutes running, smoke poured out of the motor. It is possible I fed 240v in via the 110v setting, but it is also possible that wires which came loose during the fiddling about process, I replaced wrongly. It new seems that the projector runs only on 24v via the 110v setting or something equally odd, and there a many unpleasant flashes and crackles and spittings if I change the voltage setting while the projector is running. I wonder now if my wiring diagrams, too, are up the spot. Caveat emplor!
I am getting so fed up with this machine that I feel almost inclined to pass it along to someone with greater elctrical/electronic skill who might be able to do something with it. Anyone interested?
This is a heavily-modified Pax bought off ebay. It has a B&H amp, of the type produced to replace valve amps in the old 620/630 series - see the controls at the front and the actual bit of a later B&H at the rear. It uses a 24v tachograph-controlled motor and has had the dreaded chute replaced. Gives vg sound. Compare the set-up for replacing the ghastly chute with the one in Tony Saffrey's machine shown above. A neat little unit has been fabricated to take the place of the infamous chute. I had a lot of trouble in the first instance with aligning the sound optic, because, inevitably, it had been jarred out of alignment in transit. My fingers do not work too well, so I added the knurled ring at the top end of the optic so I could get a better grip. I also improved the "padding" needed for sizing the B&H optic up to Pax hole size. This restored the sound to something like, but I felt it was a tad lacking in oomph. Being an inveterate fiddler, I decided to see what else I could do.
This is probably more pix than you need, but hey! You should imagine the sound drum being where that big cut-out is, which is why I have given you lots of views, keeping the originals because they look a bit odd when rotated to the correct alignment. I noted two things about the design. First, the brass guide roller (adjustable against a compression spring to move the film and therefore sound scanning in and out) was relieved over most of its width, so the film was only held against the roller by the rubber roller for a thin strip at either side. At the same time, the in-out adjuster spring was too strong, and was preventing the roller from turning. This is, of course, a classic recipe for scratching film. So I reduced the strength of the compression spring but immediately got a lot of warbly effect on the sound, so the sticking roller had in fact been providing the necessary smoothing before the sound drum. I strengthened the tension spring on the rubber roller, but not good enuff, so I made a new roller, completely flat across its width. This worked.
The second thing was the paired small smoothing rollers. If you look closely at the picture of the unit in place, you can see that the path of the film from sound drum to sprocket is virtually a straight line, so no smoothing, even if the spring was pulling the right way which in my view it wasn't. So I added a new anchor for the spring to make it pull the right way, and hard enough to make the film do a bit of work to get thru.
In all of this messing around I think I also fine-tuned the position of the exciter lamp and got more poke - it does seem to be extremely sensitive to the precise positioning of the exciter filament, something I have found before with the Pax. The plan now is to copy this for my bog standard Pax, to eliminate the chute. I know I have already shared with you my view as to why the chute is a bad thing, but it may bear repeating. A conventional sound drum set-up creates a fair bit of drag/inertia when starting up, but thereafter, the pull on the film is far less as it is just a matter of offsetting frictional losses, with the inertia working to keep everything moving. With the chute, of course, the drag is the same all the time and I think it is this extra pull that results in films splitting.
I have not carried out detailed comparative tests but it does not seem to me that the relatively un-modified original Pax amp (I mean on the Pax I have just re-fettled, see Page 1) was so inferior as to justify replacing it. I am finding myself increasingly in favour of restoring the original amp on projectors, even to the extent of re-building if necessary. Certainly, I am decidedly not in favour of removing and dumping original amps or making major irreversible changes so that originality cannot be restored.
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This is a very late machine I bought some time ago, with a third sprocket, permitting B&H-type smoothing for the sound. This, too, has been heavily modified. I seem to recall I was told it was a mag-only model to which optical sound has been added. I did wonder why therefore it had the lever thing on left of mag heads in the second pic, but I suspect threading for silent had to follow the sound path 'cos of the third sprocket so there had to be provision for this as well as for threading for mag. Note just above the flywheel the smoothed DC supply for the exciter, which uses a very odd lamp, I think 6v 22w and looking like a car bulb. We shall see. The rear view shows the "modern" switching arrangement using "piano" keys, which must have seemed a good idea at the time but to me seems insanely and unnecessarily complex. (Compare with nice toggle switches in the last 2 pix pinched from ebay or wherever.) It even combines the 110v/220v changeover in the same unit. And it has provision for reverse running, too. What if it goes wrong? There is a great temptation to rip the whole lot out, forget the 110v bit and just have some simple toggle switches in a more sensible location. You can see that the motor, which I had to remove to sort out, seems quite small for its job..... Note also in the penultimate pic above that there is meant to be a cover for asll those knobs on the amp, which in this case I have not got.
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This PM machine has been fighting me. It is a very late machine, with much of the amplifier on pcbs; it is away for fettling by someone who knows. It also has push-button switches rather than sensible toggle switches. As you can see from the above pic, this contributes to an insanely complex set of wiring (see close-ups in last 2 pics), compounded by provision for reverse running and switching the motor between 110 and 220v. When I got the machine, I think the motor was partially unmounted. This enabled me to see just what a Heath Robinson affair it is. The motor is shown in the second pic, which I have repeated from above. It has a long shaft on which are mounted a blower for the lamp and a pulley. The pulley is in two parts, spring-loaded on the shaft in such a way that, if the motor pulls against the shaft the pulley widens and presumably therefore reduces the drive speed. I gather from the instructions that the machine should be able to run at 16, 18 and 24fps, monitored by a stroboscope, which in my case I have not got. I imagine the exact size of belt could be pretty important.
Anyway, the movement of the motor to take advantage of the variable pulley is achieved by the mechanism at the back of the motor. In the first pic above, you can see that the motor is held in place by a spring-loaded screw on the left, and by a triangular link attached to a thumb-wheel on the right. The motor is not held at any other point; the flange simply rubs on the rear of the back plate on which the motor is mounted. The triangular link is rigidly fixed to this flange, but is able to pivot round a screw, the end of which you can see half-way up the link. (It's easier to see in the third pic, also copied from earlier). The thumbwheel has a pin on the back, which engages in a slot in the link. Turning the wheel moves the link in the slot in which its pivot is mounted and so moves the motor approximately towards or away from the drive pulley on the main mechanism shaft and so brings the variable pulley into play. The belt, of course, can only be fitted when the lamphouse is removed from the back of the main mech (pic 4).
As if all this were not enough, there are about 8 very thin wires emerging from the motor, which have to double back and pass thru the hole below and left of the motor, in which there are already 2 other groups of wires. These wires are inevitably fragile, and some had been cut back and re-soldered before I got it, and I've had to do another. The wires then do not emerge as neatly from the motor. This matters because, as ever, clearances are tight and the blower rotates close to where the wires come out and there is a real risk it will rub and sever the wires. I have had to put in spacers to avoid this risk, but it does mean the blower is further forward than it was probably meant to be. Every time the motor is moved, it puts strain on the wires and there is no guarantee they will all remain connected and functional once re-assembly is completed. It's quite possible I shall have to have the damned thing re-wound at huge expense.
The other thing I have been doing is trying to eliminate the ugly red box that had been tacked on to the rear. This carried a Bulgin input plug and a multi-pole connector which sent mains power to an external tranny AND brought the 24v feed back. There was not, apparently, space to do this within the projector envelope. In addition, the tranny was essentially dedicated to this one projector by virtue of the special plug, which was wired directly into the tranny. So I've been trying to develop a better way. More on this when I see if it actually works. It seems that the projector/lamp interlock is achieved by switching the supply to the tranny, rather than to the lamp itself, which is fed direct from the tranny.
In pic 4 above can be seen a little box with two screws, just above the shutter blade. When I opened it up, I found a cavity extending into the top of the mech, packed with some sort of stringy material. Thru this runs the wick taking oil to the cam. Inevitably, the material was quite dry so I gave it a good dose of oil before replacing it.
Returning to the ugly red box. The first job was to alter the tranny so that it had a standard euro plug mains input, and socket output for 24v. This means I can use it with any machine where I need 24v 250w. The projector end is more complex. It seemed to me that there might just be room behind the lamphouse. As you know, I am reluctant to make permanent alterations to projectors - this one has already seen too much of that. If you look at the middle pic above, you can see under the motor
where holes have been drilled to accommodate screws to hold the box and to provide a route - several routes actually - for the wires. In this pic (another repeat), you can see two chromed brackets on the rear of the lamphouse. These were used to wrap the integral mains wire round, just like a domestic vacuum cleaner. This is not something I like, so it won't be used. This gave me the idea of using the holes left by removing the lower bracket as a non-permanent fixing. I got some thickish steel plate, and tapped holes in it to correspond to the two bracket support holes and a third hole, which can be seen in the same pic just referred to, under the end of the motor, which secures the curved cover round part of the back end of the motor. This hole is lower than the other two, so the steel plate is shaped a bit like a squashed, elongated "S". Obviously, all this is much easier to understand wiv pix.
I basically started with the three connectors, which are part of the structure of the little box I have created. It was handy to have the third type of socket at the top, which I bought by accident some time ago. I inserted the little connector board under the motor because there are two separate mains feeds, the other being for the exciter lamp supply, and I didn't want more wires going to my box than I had to. I did the earths this way too. The box is secured to the projector by a screw thru the hole seen in the curved side piece in pic 1, passing thru one of the original bracket holes. You can see also an angle piece fitted to the projector, using the other bracket hole. The side of the box fits behind the angle and is then secured by self-tap screws (pic 3). Finally, a sheet of paxolin is inserted behind the box before it is fixed to the machine and a curved cover piece conceals the first of the fixing screws. The paxolin is there because, in order to shoehorn everything into the limited space, I had to remove quite a bit of the pins on the various sprockets, and I wanted a bit of extra insurance. I think the final result is not too bad in appearance, tho' I could do better if I did it again - as usual, I was just making it up as I went along.
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The question now is, does it work? Well, the answer is no and I don't know. The pilot lights come on, but the motor does not react; I got sparks from the switches and two dead resistors at one point. I haven't bothered yet to check whether the other part of the socketry works, cos I need to make up the leads.
I half-expected the motor not to work, but at the moment I cannot tell whether:-
a) the motor needs rewinding, or at least another go with the soldering iron, or even replacing;
b) there is some other fault in the complex wiring, switching or old solder joints etc;
c) I have done something wrong or failed to understand some part of how it should work.
LATER
I sent the motor away to a rewinding company, who confirm that the motor am indeed cooked. I have a theory as to how this happened. At the back of the switch panel is a micro-switch which , on close investigation, acts as a momentary-only push-to-make for a 30uF cap, which I assume to be the start capacitor for the motor. Only the switch didnae work like that - it was on permanently. This, as you probably know, is not a good thing, rather like the centrifugal capacitor-disconnect system in Debrie motors when it stops working.
The first pic (another repeat!) shows the micro-switch (or is it a reed switch?) in situ - it's a location that is fairly obviously liable to damage if the back is removed. The close-ups show the switch first with the motor switch off, then on. In the latter, you can just see there is still a tiny gap; to close this, the motor switch has to be pushed beyond the on position, against a spring. Some confirmation of this theory came from a guy in Spain who had seen pix on my site and said the motor on his (16mm) PM ran hot. When he adjusted the micro-switch at my suggestion, it no longer did so.
I sent the motor away for repair, but it apparently can't be done in a way that would allow it to fit back into the machine wiring system without a wiring diagram, and can't be done at all for the two voltages - it would have to be 240v only. So I have asked various people who might know of one (diagram, that is), but my hopes are not high. I don't recall Pathé ever going in for repair manuals etc, and I suspect few if any existed outside Pathé themselves. As a precaution, I purchased on ebay a 2-sprocket silent version (thanks to Terry Vacani for the tip) which seems almost identical, to the extent of having a few bits relevant to the sound machine but not the silent. I am now attempting to draw up a wiring diagram myself, based mainly on the silent machine, which has had little if any alteration, unlike my sound one. It's the sort of thing that does my head in. I spose I could just transplant the motor, but I am a tad reluctant without exploring the possibility of keeping both running.
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One project I have been plugging away at is trying to trace the wiring of the PM. It is about as insanely complicated as I thought. Here are the main parts of wot I have found - no guarantees, mind , E&OE etc.
I have also, with huge labour and difficulty, produced as good a version as I can make of a virtually illegible and certainly un-photocopyable "blueprint" (it's mainly pinkish, actually) of the amplifier circuit diagram. I'm sure I haven't got it all right, as it really is hard to decipher, so if there is anyone out there who can correct me, I would be glad to hear. Here are some pix of the amp and the circuit
As you can see, it is a "transitional" amp, presumably made on the cusp of the change from valve to transistor amps, with a number of separate PCBs as well as valves.
The switch wiring diagrams are actually based on the silent version of the PM, labelled simply the P, which I acquired on ebay. It seems to have the socket for the neon strobe light, the amp connection in the base of the lamphouse and a gear on the back of the second sprocket which would mesh with one on the extra sprocket on the sound version. And for all I can see, the wiring is identical. I spose I could transplant the motor to the sound machine, but at present I am not so minded. I don't actually think much of this motor. I don't like the variable pulley, or the dodgy positioning of the start cap microswitch (and I am clearly not the only one to experience the problem) which renders it likely to be knocked into a permanent "on" position. All I am really interested in is optical sound (it's not as tho' there are masses of mag film out there). Also I hate push-button controls - too plastic. It looks to me as tho' the entire motor, switch panel and caps could be removed as a unit and preserved for a possible future purist willing to pay to have the motor re-wound. It should then be possible to use one of those B&H DC motors and run it from the lamp supply (with rectification, of coarse). Has anyone actually done this? A machine with a single external 24v supply would be so much easier.... And I could fit some nice, positive, metal toggle switches. Anyway, back burner for now for mature reflection.
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