Once more into the breach

I have struggled endlessly with the L516 curved gate and the exciter lamp holder that I have showed you in previous episodes of this saga. In recent months (Autumn 2020) I have made yet another attempt, turning the gate thru 180 degrees as it had become apparent that at least one part of the problem was that the sound gate did not line up with the film as it emerged from the gate, which I could only correct by reversing the thing. Here are a couple of pix of what may be its last incarnation. 

I have also made inumerable attempts to use a flywheel, using a set-up I inherited with a machine I acquired. I remade most of the parts but still failed utterly to get the flywheel to rotate cleanly - there was always a wobble I simply could not correct.

So in the end, I decided to go back to basics and look at my most recently acquired machine which had come complete with its original sound gate/smoothing thingy. The idea is to copy it for other machines such as the one where I have been failing for so long.

 The basic concept is of a thin metal strip held by a spring onto the sprocket edge of the film, which is riding on the curved block(pix 4-6). This is best seen in pic 5. The actual execution, however, is far from simple. A long screw passes thru from the front of the block to a small shouldered  thingy (not at all sure what to call it), which provides a lug for the spring, tension of which can be varied by turning the thingy. This in trun seems to require rather precise work to provide an axis on which the arm can pivot, while being loose enough to allow the arm actually to pivot, so that the length of thread on the long screw seems to be critical. One end of the steel strip fits into an amazingly narrow slit in the spigot at the very rear of the arm (pic 7 extreme right), and a tiny screw passes thru the strip. The other end of the thin strip has a similar arrangement. The slit in this case is in the shaft that carries the film guide roller, which isn't a roller at all but is fixed and forms the outer guide for the film at the beginning; after that, the film is left to sort itself out. I must say I was very sceptical about this arrangement but, reasoning that it must have worked at least tolerably in the early days decided to give it a go and see. All the 16mm conversions I have seen, incidentally, have a completely different set-up.

I have managed to fabricate a couple of blocks but haven't gotten any further yet, partly because I wanted actually to test the original before doing any more and partly because it looked very difficult. Was there a correct type of steel needed for the thin strip? How on earth was I to cut one with smooth enuff edges? Could I match the spring arrangement? And, most of all, how could I reproduce the tiny slits?

I was forced to address some of these questions quite early on; close examination revealed that there was a tear in one edge of the strip in the only original I had. I was not prepared to risk the horrendous damage that would occur if it got worse. So I was forced to make a new strip before I could go any further. In the end I made one by sandwiching the strip between straight edges for cutting and drilling. I then had to make a second because the first was slightly too short and did not allow the film guide at the front end to fit into its recess. Yet another critical dimension. I am pondering using two separate pices to simulate the slit for the strip, but I am not looking forward to the manipulation of tiny parts that will be involved.

This was only one part of the problem. I was never fully satisfied with the exciter lamp arrangement I had devised - there didn't seem to be enough light getting thru to the screen.  So I decided to have a go at something I have frequently pondered, ie whether an LED could do the job. With my lamentable lack of electronic knowledge, I then had to try to learn what I would need to do. This was not helped by the problem of getting info about the LEDs so as to figure out what resistance would be needed. They arrived with no info at all; it was on a website apparently but even this varied between suppliers and terminology was inexact, inconsistent and variable. One is supposed to just know this stuff, it seems. In the end I proceeded by the tried and trusted method of trial and error. The one consistent piece of info was the working current an LED needed - fortunately, peak current is much higher than working current so there is some leeway. So I tested various resistors, starting high and working down. I think I ended up with 150 ohms for a 5mm LED with a light output of 30,000 millicandles. I can write these things but it don't mean I understand them. I mounted this thru a block of aluminium which in turn sits on top of a Vox sound telescope mounted in a sleeve in the holder for the original telescope. On testing, the new metal strip in the old block worked well and gave no problems with the film and sound was encouraging; however, the sound seemed very sensitive to focus and position, neither of which are easily adjustable with this set-up. I am now pondering using a full Vox-style st-up with its integral focus and postion adjustment, probably by reproducing the relevant part of the Vox sound head/drum assembly and stealing a telescope and its holder from an unsuspecting Vox. (I once tried to make a replacement holder - they often get cracked/busted). I didn't completely succed but got far enuff to see how it could be done if I nneded to. Must dig it out again - I did see it around quite recently. And I have several unused telescopes I acquired in France as spares.) Remember, there is limited space between the top of the original sound telescope and the bottom of the lamphouse so I could not fit an LED on top of that. My alterations to fit the HID lamp ruled out fitting the LED inside the lamphouse, so I have not yet considered in detail what may be possible on that front.

 I have spent much of the last two days doing exactly what I was suggesting, ie building a mounting plate for a standard Vox sound telescope unit. Both it and the LED exciter work well. As indeed does my fingers-crossed repair of the sound smoothing unit. Must copy both asap. Will do you some pix. And here they are.

The first two pix m show the bracket, made from a chunk of 6.25mm/0.25" aluminium bracket I had lying around. The part with the through slots in sits at the top level of the sound unit, which originally had 3 screws (two of them in line) holding down a curved bracket for the original sound telescope. The back corner is cut away because the picture head unit is at the same level and its base gets in the way. The slots were to allow for easier fitting and easy adjustment. The first thing you will notice is that there is a blob added at one side. This is because the intrusion of the picture head that required the corner to be cut off led me to assume that the vertical and horizontal parts needed to be cut to the same width. When I came to try to fit the Vox sound reader shown in pic 3, one of the screws fell just beyond the edge so I had to add a bit to make room for the screw hole, which in fact falls right on the join between plate and blob.  The second thing you will notice is the grooves to fit the back of the Vox sound reader into, one being a deep rectangular section, the other a rather shollower V groove. Pix 3-6 show the alu block I set up as a test bed to try various different values of resistor without undoing the rest of the wiring. The hole in the bottom fits over the top of the Vox sound telescope tube and is held on by a screw (front of pic 4). In a thru hole sits the 5mm LED. I have some 10mm I must try some time. I used the same power supply as I had fitted for the earlier version of the sound reader which I assume delivers about 4v into load but which registers 9.5 without load.

Update January 2021

I have continued working on the sound unit. I have made a new block to take a 10mm LED and I seem to be getting somwhere with the sound. It has been too high-pitches, sharp and distrorted and I suspect the problem now may be too much light. I have fitted a red filter in the sound telescope which seems to help a bit; I am now considering a diffuse LED rather than the water-clear I am presently using. Then there is the photodiode to consider - maybe that might help. I know results can be better because I also have the unaltered (apart from replacing PEC with diode) machine upstairs, which gives markedly better sound. Maybe the Vox sound slit is just too small. All of this messing about with the sound is to accommodate an HID lamp rather than the orignal 15v 200w or a modern 15v 150w dichroic. I am also getting a lot of hum - there are plentiful possible sources for this eg switched mode power supplies for the fan and exciter, or it could be a characteristic of LEDs or the various 110 volt trannies (one each for projector and amp). So some way to go yet before I can declare this over.

I have bottled out re the sound unit and have not attempted to emulate the spring strip of the original, though the other machine retains it. Instead, I have adapted the design slightly to include a runner roller to do the smoothing. Here are some pix, including one of the complete set-up. Mechanically, it all seems to work OK.

You will see on earlier pages some stuff about guide rollers for the lower sprocket - here is a repeat of one of the pix.

The sprocket turrets and these guide rollers seem to take a bit of a battering on the Rural. The turrets suffer from Mazac disease and the rollers seem to have been replaced in many cases. The approach shown in this first pic looks terribly Heath Robinson, but it does have a couple of useful points - it has a "wrap-round" so it is difficult for the film to leave the sprocket (just like the Vox) but in this case with the lower roller sprung to smooth things out a bit  between take-up and sprocketand back thru to the sound head. But it don't look right. 

This more recent attempt (pic 2) is based on half of a roller frame I discovered among my bits and pieces. That gave me the shape of the curved sides and the location of some of the guide rollers. I then had to fix axles for the rollers that also served to hold the frame together and make sure the rollers rode in the correct position, and make rollers to an exact size. A long and fiddly job but it does seem to work. It does however need a fairly complete turret to work. As you can see, it still does a wrap-round, albeit in a different way, though I would still in principle like a sprung roller before the take-up.

The above is just a string of pix of turrets on some of my machines that I took for a friend. The one in pix 7 and 8 looks good but is not very successful. The best one appears to the one in Pic 2

January 2021

Here's a bit of detailed restoration sort of stuff - it's about the 17.5 Rural. 
The original silent Rural was introduced in 1927, too long after 16mm to have much chance in markets outside France. In 1933, a piece of clever engineering added an extra layer to the existing two tiers to create the Rural Sonore. Then in 1941 the Germans demanded that all 17.5 machines be converted to 16mm. Some did survive as 17.5, but most were converted. The original Rural silent had only 500' capacity - a single reel. The sound machines had longer arms, to suit the 1000'  (2 Reel) spools that became the norm for features and the like. This was not good enough for 16mm of course, so yet more adaptation increased capacity to 1600', which I think will be just enough to take a 2000' spool, to make life a bit easier for projectionists showing 8 and 10 reel features.
I am gradually getting to the point. I wanted the bigger (1000') spools for my 2 silent Rurals, so when I acquired some 16mm versions of the Rural Sonore it was party with an eye to stealing their spool arms as well as various other common parts. Given that some of the 16mm machines came without arms, the net result has been a shortage of said arms, so I am having to re-condition those I have got as best I can - and not all of them are complete. The one I have just been dealing with has the take-up assembly missing from the lower arm. I have therefore stolen one from the now-unused 500' arms and in the process discovered a style of friction brake I had not previously seen. Yer tiz.



 The friction is provided by the four little "brushes" bottom left. The springs fit in the transverse holes thru the adjacent disc, which holes are partly exposed as seen. The brushes fit one either end of the springs, and the disc, spring and brush unit fits into thehole provided in the pulley wheel bottom right. The rest is obvious.
Experience in recent weeks testing a Rural Sonore makes me feel that this friction mech is necessary for correct functioning of the machine. The drive to the take-up is a standard wire spring belt but it needs to be thick and fairly stiff to work. This in turn means that the springing is too stiff to rely on the flexibility of the spring to avoid ecxess stress as the film comes over the bottom sprocket, as many small projectors do.
I very much doubt that the assembly has ever been taken apart since 1927 as it was so filthy and it took a bit of work to remove the accumulated gunge of the years.

26th January 2021

Although it's a bit esoteric, this is after all just a blog about what I have been doing, so...........

                         

This is the sound unit for a 16mm Rural Sonore. I am looking at the possibilities of conversion to 17.5 by running the film thru the "wrong" (for 17.5) way, not so much because of the sound unit but because of the problems with the claw and cam. My previous attempts to dismantle one of this design failed because of the difficulty of getting the sound drum out, which is held in 2 ball bearings and did not want to shift. In the end, I 'it it wiv a 'ammer (cushioned by a piece of wood). Note the clever design which provides a big space for the motor capacitor and the sound drum, exciter (from the projector main lamp) and photocell, all in a single layer which could mount directly between the silent Rural's base and mech sections. This 16mm version obviously followed on from an original design for 17.5. Below is a pic of my 16mm (working) Rural Sonore with a similar soundhead, which may make the above easier to understand. 

As usual, the paint was coming away in large areas, with some aluminium rust (you know, that white stuff that so often appears on elderly alu etc  castings), so I decided to strip it back. This reveals how rouigh and ready the casting is in places. The fettling (this is, I believe. the correct technical term for machining the rough bits from raw castings) is precise only where it needs to be, eg in the tube that contains the bearings - Pic one far left. Elsewhere, it was a lower standard - see pics 2-3. In fact, pix 3 and 4 make me wonder if the square section and the twiddly bits were made separately (which would be a lot easier to cast) and welded together after. The problem is that one cannot realistically re-paint over the old - it just looks scruffy, but duplicating the very thick paint finish that hides the multitude of underlying sins is a problem. Hand painting never looks right, but spray is pretty thin and shows all the dodgy bits. There is also the question of adhesion - one of the reasons so many old machines tend to lose their paint finish is that alu etc needs a special etch primer for the paint to stick, and the correct procedure was not always followed. I have a Vox that is almost bald because I was able to flake the paint off with little effort.

Pic 5 shows the bits that survived to now. The sound drum - necessarily very small because of the design - is basically a single unit comprising the shaft with drum, 2 ball bearing and a spacer to go between them. The ball bearings had seized up, but improved with soaking in white spirit and oiling. I spose they would work, but I would ideally like to replace them. I have however discovered that while bearings with a 10mm centre, 26mm outside diameter and 8mm thick are ten a penny. Unfortunately, these ones are 25mm diameter and a preliminary search has completely failed to find any. Usually in the past I have easily been able to source replacements on various French machines as they have been standard metric sizes.
The tube for the photcell is obvious in the pix, but the little cone thing, which has a curved mirror placed across its axis, puzzles me as I have seen only direct reading versions before. It must have worked tho'. The pressure roller for the sound drum is really crude - mounted on an arm that is just a piece of steel twisted to the required shape.

 BB1 BB2C Home Talkie Super Rural