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PATHÉ VOX & SUPER VOX

So much of my projector life has been about these machines, so it's time they had their own page.

I have a number of Vox's and Super Vox's, partial and complete. The V/SV has always been one of my favourites, partly for nostalgia - an SV was my first introduction to 9.5 and I still have the one I got on my 21st birthday - and partly because I think they are particularly kind to film. One of my many projects is sorting them all out. On a parallel track, I have long been looking for a replacement for the old MS4B/BPY10 etc photo-diodes/solar cells I used to fit to Vox's and which gave such good sound. I have just acquired a number of possible things from the USA, which might do the job, so I needed a test bed, and a Vox would be ideal.

The one I turned to I had never examined before. It turned out to be a standard Vox which had been converted to 12v 100w lighting, using a lampholder attached to an old Vox lamp base. Why 12v I cannot imagine, as the 15v 150w provides a direct replacement for the 15v 200w original without going to all the trouble of removing the tranny and installing a new one. Here are before and after diagrams I drew up, mostly because I find it hard to get my head around this sort of stuff without them. As so often happens, the conversion was half-hearted and unfinished, so I had a fair bit to do. I replaced the motor condenser on general principles, as they are readily available from Maplin. I will try to find an original Vox lamp switch in due course, but for now I have made do with a DPDT that allows the pilot light to operate when the machine is not running and provides a motor/lamp interlock. I also replaced the power inlet with a standard Euro mains socket mounted in an aluminium plate which replaces the old socket arrangement. I couldn't see a way to make safe the old plug which originally carried the projector supply (at 110v, not 240v!) through from the amplifier. The old plug with its three evenly-spaced pins could be inserted the wrong way round, rendering the whole machine live.

The sound reader was not much use either - I couldn't get it to adjust to scan the track properly. I fitted some extra strips on the back which, although not perfect, does get the scanning beam in the right place. I also found I was getting a lot of stray light onto the film, apparently from the sound telescope itself, which I thought could well interfere with the sound so, experimentally, I have fitted a doover to block this.

You might observe, with some justification, that I allow myself to get distracted into all sorts of byways. However, it is precisely what I like doing. I have now moved forward on the original sound cell test bed idea by making an initial mock-up of a bracket to fit in place of the sound mirror bracket, onto which I can mount various cells. As you will see from the pic of the real thing, it is not as neat and clear-cut as the diagram would have you believe, but should you ever want to make one yourself. this would at least give you a start. I have made it in wood (hardwood, oak in this case, as ordinary pine splits too readily) to avoid any possible problem with shorting. Actually, I now think I shall cover the flat area with insulation tape anyway, to facilitate removal, as I plan to stick the cell to be tested to the bracket with insulating rubber solution (have I told you about this? Ask if not).

OK, so the wooden one didn't work, it just split. If anyone is minded to say I could have told you so, just remember, nobody likes a smartass. Anyway, it lasted long enough to provide proof of concept and encourage me to invest the time in making one out of steel. I say one, but in fact I mean more than that. Left shows the profile, right that I made in a strip about 6" long. When I need one, I just have to cut a bit off and make a hole for the fixing screw. The measurements have crept a bit, too, and I chopped a corner off; I'll add the changes to the original drawing in brackets and re-insert it. Note also that the hole will need slight re-location. I think the part where the hole goes is going to be too short and the hole will be a slot - it will still work, but a hole would be better.

The rest of my time was taken up with trying to figure out how to make a new motor end cap for a Super Vox, having found one suffering from the dreaded Mazac disease. This is a lot more difficult than the Rural one I did previously, as the bracket for the cross-gear and the motor mounting lugs are part of the same casting/moulding. So far, my thought is that I make a round jobbie first, exactly as per the Rural, then seek to add the sticky-out bits (technical term for bracket or lug) afterwards. (NB While making the cap, I found an error in my first drawing (left), so what you now see is an amended version). So far, it's all been measuring and drawing, tho' I have been able to use my new-found electronic repair skills to clean up the drawings a bit from the hideous mess of rubbings-out etc. Got more drawings to do yet. Have also acquired a mini drawing board so I can finally draw lines with some hope they will be parallel and square to each other.

These are taken from one in good condition. Same "floating" bearing design as Rural, but a "notch" in the bearing itself and rings and oiler material shaped to fit.

Here are the additional drawings. I may now have to make a start on actually making one unless, of course, I allow myself to be distracted off down another part of the labyrinth that is Chateau Nerdistan....

Back to my little bracket. I've decided after all that a slot is better than a hole anyway - I can leave the retaining screw just loosened but in place and still remove the bracket.

Here are some pics of back and front of the diodes I want to test. For scale, the long thin one is about 9 x 3mm; the bigger square one about 7mm square, so pretty close to the old MS4B. Sorry the pix aren't to clear, as it's hard to see the smaller ones; these are going to need wires soldering on, not my strong suit at this sort of mini-scale. The one on the far left may even still be in its packet. No it isn't; I've wired it up - the backing plate may be ceramic.

What I have done is to give a bracket a couple of coats of rubber solution and allow to dry. Then a bit of rubber on the back of the diode, and place carefully on the bracket, (basically, this is just gluing it in place), checking where it needs to be in relation to where the light comes down from the film. This is not extremely critical, as I believe that once the light has passed thru the film, properly focussed etc, the picking up of the light is a much more tolerant matter. So far I have tested the long thin one, which seems to work fine, so I expect the big square one to be good. There may be a problem with these and ambient light, however; they may be big enough and stick out enough to pick up a lot of hum if there's much light about.

Later. The big one is good, so is the ceramic one. Both work well. I am playing, incidentally, thru the little pre-amp from Maplin I made up years ago and which, of course, they no longer supply. I've added one of those ready-made regulated power supplies, which I think gives better results as the voltage is well up and stays there. Even No.3 works! I can't really detect a lot of difference between them all, even tho' some have enhanced red sensitivity and some blue. Left you can see the entire test-bed set-up. I've run a screened wire through to the rear of the sound unit and out the back to the pre-amp. At the front, it comes to a little terminal block fixed to the machine - I don't normally like to do this, but we are talking about 1.5 very small holes I can easily re-fill if I ever get around to a full re-paint. (Incidentally, the hole for the little brass retaining strip was already there). I have some thin wire which, stiffened by a light touch of solder, serves as pins for the sockets in the terminal block. Right is a closer view of a bracket with a diode. I can now interchange my four different types of diode at will, especially useful when it comes to the next phase which is, of course, to experiment with using LED's to provide the light, instead of the main lamp as in the Vox or a standard exciter. I'll let you know how that goes.

I got these things from Digi-Key in the USA. It does have a UK presence tho' at UK.digi-key.com. There is a search-by part-number function; Catalogue numbers (page 1615 in my paper copy) from left to right are:-

PDB-C165-ND; PDB-C171SMCT-ND; PDB-C607-2ND; PDB-C609-2-ND.

You have to be very precise searching by these part numbers - it insists on every dash. When you get to the page, scroll down a few inches to a table with Technical Catalog Information and the part number as the first line. Click on the part number, then on Datasheet on the following screen to get a pdf. file with pix and spec. Prices range from under £2 to about £6, ex-vat and shipping of course, but are substantially reduced for 5 (25 for some) or more.

Been working on a Super Vox. The internal wiring's a bit manky in places, but the main concern is the usual lack of any earth connection. I tend therefore to re-wire them a bit, using the third pin, which is shorted with its neighbour usually, as earth. The effect of this is, of course, that if you were to attach a standard Vox transformer, the entire casing would be live, so the tranny needs re-wiring, too. See pic for the new wiring. I find I need to draw it out to get it straight in my head and even then I'm not sure. The motor/condenser wiring always fools me - there are four wires, but instead of 2 to condenser and two to motor supply, two of the four are connected to the same place. I think there is also an element of the tranny being used as an auto-transformer to feed the motor (and the pilot light) when one uses a 130v feed, not that one ever does in practice. So I'm not entirely sure the diagram reflects reality, so don't rely on it absolutely. Once I found that whatever I had actually done made the projector work, I sort of let it pass.

Ben reading some of the quite detailed (standard)  Vox operating instructions in Le Cinéma Chez Soi, and picked up one or two points of interest I either didn't know or hadn't thought much about. I didn't realise that the speaker plug was so wired that it acted as an amplifier switch - no speaker, no power to the amp. Given that valve amps don't like running without a speaker, this is good sense. Incidentally, here for those interested in such things is a circuit diagram for a Vox amplifier.

Far more emphasis than I had realised was given to the fact that, more often than not, the Vox needed a manual assist to start, although this is not really my experience - maybe they were stiffer when new! What was obviously happening was that the usual idiots were switching the machine off with the motor switch and leaving the lamp switch on. When starting up again, the lamp would come on at once and, if the motor failed to start, the film got burnt. No doubt some of them also managed to cook the motor to boot.

There is also reference to the effect of variations in voltage. Being an induction/synchronous type, the motor had tolerance for some variation without the speed being affected, but too high or too low a voltage and the speed and therefore the sound would be affected. I wonder if this was ever the cause of some of the famous "wow" you could get from a Vox. Not only that, the UK electricity board used to control load not just by voltage but also by varying the cycle rate. I wonder if a regulated 110v input might actually make a difference? Anyone any idea?

Here is a blueprint for a Vox (actually "S") projector claw. This is the nearest I've ever seen to a spec showing just how a Vox claw (and its chariot) should look.  I have also enlarged the most important areas. I have tried to get it as clean as possible without losing detail - the original comes out all dark on scan. There are some interesting features, notably the apparent intention to fit a pin to the top of the claw as an anchor point for a spring. I have a machine I believe to be an original "S", which doesn't have this arrangement; indeed it has no spring at all, something I had not previously noticed. There is an anchor point below the claw, however, so it has presumably just gone AWOL at some point. My Vox has the usual hairpin-like spring and the Super Vox, of course, has a different arrangement again, with a coiled spring attached to a "leg" added to the rear of the claw. The effect of these springs in action seems to be to resist the downward throw of the claw and, in the case of the Super Vox at least, to resist also the withdrawing stage. The springs then give the claw a boost on it's upward shift.

There is presumably a good reason for this but I don't understand at the moment. Prima facie, one would expect the claw to get spring assistance for the down stroke, where there is most work and speed is of the essence, but in fact we have the complete opposite. Can anyone enlighten me?

The spring seems to have been one from the "B" projector, presumably the 200B. I can't get the chronology straight in my head here - when was the "H" introduced, with the Super Vox style of claw?

I did make some progress with my Super Vox end cap. I have completed the round part, which seems to fit OK, tho' I have not fitted the bearing and run the motor. I have also had a go at fitting the lugs which fix it to the base of the projector. These are fixed with a 2.5mm screw thru the narrow triangular bit, and a 3mm thru the full length to the side. The top end of each lug is curved to be an exact fit to the round part. I haven't got it quite right - I don't think the legs are in quite the right place, but I think it's close enough to be workable. I've made one leg too short - may have to fix an extra bit on here as for the Rural qv. I now have to make a bracket to carry the cross gear - getting this lined up right is going to be very tricky.

Since I've been using my trusty old Super Vox to test run films, I have noticed one or two problems, viz a) seemed to be running a bit stiff; b) lot of light spill round sound telescope (more a problem of getting in my eyes when watching films than of effect on sound); c) lamphouse getting rather hot and possibly motor, too. So decided to do a quick 50,000 mile service.

It is, of course, never simple. The stiff running was easy - there was no end play at all on the motor so I just took off the fan cover and eased the fan back to give a bit of play.

Light spill was more difficult. The problem is that the hole in the bottom of the lamphouse is oversize, to allow for alignment problems and of course for movement of the telescope. The little round light guard that sits over the telescope is not quite big enough, but it can't really be made bigger without the risk of fouling some part of the lamphouse and restricting movement of the telescope. I decided a flat plate to sit on the floor of the lamphouse could cover more of the hole, leaving the telescope light guard free to move on top of the plate. Here is a not very good pic, but it shows what I mean. The hole needs to be about 16 x 20mm (mine's a bit oversize in places). This is a view looking as from the back of the machine - the distance between (top as viewed here) edge and the hole is about 15mm. On the left, it's about 1/4 of an inch (sorry). Overall size of the plate is about 37.5 x 45mm.

 The other mistake I made was to use material that is far too thick - the round thingy sits rather precariously on top, but it does actually do a very good job. Something very thin, possibly glued down to avoid bending? The other thing to watch out for is the inner lamphouse cover - the edge fits well inside the lamphouse and the plate needs to be truncated to avoid it. All this was a bit laborious and trial-and-error; so much for quick. While I was in the lamphouse, I decided to replace the cracked condenser and clean the sound optic. All this fiddling made the wire from the tranny look a bit manky, so I replaced that too. The lamp also chose this moment to give up the ghost. Sadly, it was only after I had reassembled everything and seen the result on the screen that I dimly recalled that the lamp pins (we're talking 24v 250w peanut mounted on its side with holder on the inner lamphouse) needed cutting short to get the filament in the right place.

I also replaced the motor condenser. I have a vague idea that condensers can lose the plot with time and that this can cause the motor to work harder and get hot - anyone know if this is true? As new ones are readily available from Maplin, might as well replace. The original was 10uF and I only had 8uF to hand, but it seems to work fine.

The other part of the heating problem was lack of cooling. When converted to 24v 250w (done by unwinding some of the tranny coils), the mirror was detached from the rear of the inner lamphouse and re-fitted closer to the lamp. This left a lot of gap where air could escape without doing much cooling, so I covered the hole left by moving the mirror with a sheet of aluminium cut to size. I have heard that these QI lamps may not be keen on overmuch cooling, so I may have to reverse this at some point, or fit some kind of internal baffle. Incidentally, I have experimented with the dichroic mirror version - it seemed to deliver a lot of heat but little extra light.

Longer experience with these alterations to the Super Vox suggest I shall have to unpick most of them. Contrary to my expectation, the lamphouse is much hotter. This makes me wonder if maybe there wasn't always a fault here? S. Voxes always ran very hot with the original lamps. Also, there seems no doubt the motor is a tad more sluggish starting, so I've now got a 10mF capacitor.

Oh dear. I feel such a fool. Having unpicked some of my Super Vox changes 'cos it was running too hot, it still ran hot. I finally figured out why; when I eased the motor by shifting the fan back a fraction, I must have failed to do it up tight enough. No fan rotation = no cooling. Doh! Now I shall have to re-do the lamphouse bit as the light spill from it is actually quite irritating. Let this be a lesson to me not to go at things like a bull at a gate.