This is the report I wrote to the projector owner on the alternative solution of fitting a tungsten halogen lamp in place of a disappointing attempt to fit an HID-150 mirror lamp to a post-37 DA. This was, of course, done before the idea of the HID-type route had really taken hold in my slow brain.

"Have done the  QI conversion on the other DA. As usual, there was a long string of things actually to do that are not apparent at first sight. Even before I really started, I had to lever off the double pulley on the back that drives the take-up and rewind belts, which had seized itself solid to the shaft. I sanded the shaft down a bit to re-fit. I discovered on final testing that there was not a lot of point, as it appears that you do not have a working reverse setting. I had a quick look at the switch, but there was nothing obviously wrong, which meant the fault was probably inside the switch or even perhaps in the motor wiring. I felt discretion was the better part of valour here as you don’t use it anyway.

Now on to the meat of what I needed to do.

1.   Strip out internals of lamphouse cover. So the condenser lens housing, held in by those tiny screws on the side (one always sticks), has to go, and then nuts have to be fitted to the tiny screws to avoid light leakage. Ditto mirror mounting at the back, only a bigger screw, and similar for the inner lamp sleeve, which attaches to the lamphouse top.

2.   Once inside, there’s the actual lamp holder. To disconnect the wires, you have to remove the plastic insert holding the actual lamp socket from the steel cylinder it is mounted in. Only it does a sort of plastic Mazac thing and won’t budge without much brute force (hammer and large wooden dowel), so the socket got well bashed. I didn’t want to cut the wires, which I have left in place in the base, terminated in a connecting strip to keep them out of the way.

3.   Then we have to measure out and make up a bracket that can hold the lamp at the right height with a bit of fore and aft adjustment to get best light without burning the film and fix metal strips to hold the lamp, plus make a fairly round hole for the light to go through. This lamp is a “force” fit into the slot that takes the raised bit on the front edge of the mirror. You may need to do a bit of re-bending of strips if you ever have to fit a new lamp. Looking thru from the front without the lens in place gives a good view of the lamp for centralising. When it comes to fixing the holder in place, note it does matter which way up you put the metal strip under the hexagons.

4.   The base plate had to come off to sort the wires. One of the screws was rusted solid and had to be drilled out, which buggered the socket, so I had to apply some of that hard-setting putty and make a new thread. Do not tighten screws too tight! I sanded the base plate to get rid of the worst of the rust and gave it a couple of coats of acrylic. Not perfect but better. The rubber feet had almost vanished above “surface” level so I tried an experiment. In the past, I have used the full height of replacement feet, and then found it stopped the machine fitting in the wooden box – lid wouldn’t close (not that you have a box in this case). This time I cropped the feet to give a racy low profile.

5.   Then the wires from the lamp were just too short to reach direct to the input connector strip below the floor of the lamphouse, so I had to fit a second connector strip inside and fit linking wires. Nothing can ever be simple.

6.   All you need now is a 15v 150w power supply. These are available on the internet, and usually will take either 110v or 240v input without adjustment. Unfortunately, these are “switched mode”, not normal trannies, and will not power a lamp from cold without a kick-start. This takes the form of a thermistor in circuit for cold start, to be switched out almost instantly to avoid overheating, leaving the lamp in direct circuit as soon as it starts up. I do this by way of a centre-off switch (“on-off-on”), with the thermistor in circuit for the “up” position, then a quick shove across the centre “off” to the lower “on”, which is direct feed (although I wonder, thinking about it, if an “(on)-off-on” wouldn’t be better, with the spring-loaded momentary (on) preventing any risk of melting the thermistors. See final comment in (5) above.

You may be lucky enough to find a tranny instead, but they are rare. The 24v type of tranny is slightly more common but such a lamp would have little or no chance of avoiding burning the film. More details about using a switched mode power supply are at page 3 above. Or you could go with a 12v 100w lamp, power supplies for which are much easier to find. You could even use the defective reverse as a motor on-off switch, with the 12v supply separately switched, as a full interlock is not really needed here. What a pity that the need to accurately place the HID lamp at 32mm from the plane of the film meant we couldn’t use one to any great effect, tho’ I have yet to pursue using one of the peanut type with the existing condenser etc set-up. Have heard no more about LED’s either.

Final testing showed a full 30 seconds of still frame without any sign of heat damage to the film, tho’ you will obviously wish to do your own testing as well."

You may well understand that by the time I had finished writing this, I was seriously beginning to wonder if the best way to convert a Bolex DA/PA might lie in the peanut equivalent of the HID lamp, an NSD-150. So I promptly tried this, using as a test bed a pre-37 machine (a PA, in fact) simply by putting a metal bar with a snug fit into the original lamp socket and mounting the HID lamp socket to that. Height is not too critical as there is plenty of adjustment up and down with the original holder, and centring takes care of itself. There is also some fore and aft movement from the mounting plate for the original.

I made quite an elaborate douser arrangement when I converted the DA above, but decided to go simpler this time. Here is a pic.



Working from left to right we have the douser plate, with folded sides that wrap round the condenser lens housing and help keep the plate in place. A brass rod serves to make the step across from the position of the condenser lens to the centre line of the lamphouse. The centre of the lamphouse cap is drilled out, starting from the hole where the inner lamp sleeve was fitted. I tapped the hole in the lamphouse cap to M3, then made a brass sleeve piece with a 1.5mm bore for the activating rod and an M3 thread to screw it into place. The plastic knob is a late addition when I found the original metal knob I fitted got too hot. It seems to work ok, tho' I am wondering if the metal plate of the douser is not a bit flimsy. Time will tell. What I can tell you is the new lamp gives a good, white light, significantly brighter than a tunsten halogen lamp. There are no visible signs on the screen of over-heating of the film after a full 30 seconds. I am putting the difference from the reflector lamp discussed above down to factors such as the intervening condenser lens obviating the need for additional  heat filtering.

A big advantage of the HID type of lamp is the small size of the necessary power pack, which would fit easily inside the kind of base box described on page 3 above. This bulb could provide a solution for other projectors where it is not possible to achieve that 32mm film to lamp distance that is essential for the HID-150 mirror lamp. And it looks to be a much simpler conversion.....

The bad news is that both the HID mirror lamp and the equivalent peanut bulb may disappear from the market because of new rules - they seem to contain mercury or summat, and neither manufacture nor disposal is environmentally friendly.

------------------------------------------------------------------------------------------------------------------------------------------------------

Discovered the other day an odd little quirk of the Bolex whixh I had not encountered before. As machines get older, I thought it might be sensible to record it here.

This is a rather badly-drawn exploded picture of the double pulley on the rear of a Bolex DA that drives the take-up and the rewind belts. The actual pulley as seen is also shown.



The turquoise section is held firmly to the central shaft providing the drive by a grubscrew in the hole marked. Each of the side pieces has a central bore that is able to pass over the lip on its respective side to rest up against the side of the centre section of the turquoise bit when properly assembled – see photo.

This is where it gets complicated. The “trough” between the side lips and the central section of the turquoise bit is grooved around its perimeter to a gradually increasing extent until it reaches a maximum depth, at which point there is a step.  This is basically a form of ratchet. The slider goes into the grubscrew hole in the pulley, followed by a spring, then finally the grubscrew itself. When the turquoise bit rotates, the slider goes round the perimeter of the “trough” until it stops because the spring has driven it into the deepest part of the groove and the turquoise section then drives the pulley. If rotation is in the opposite direction, the slider enters the groove from the deep end, pushed in by the spring and gradually emerging from the groove against the pressure of the spring as rotation continues. There is then no drive to the pulley. This action of the slider is also what stops the pulley part just falling off.

However, the really difficult part of all this is that none of the slider, spring or grubscrew, shown enlarged under the drawing of the pulley, is more than about one eighth of an inch in length and even less in diameter.

I got into this digression because when I was attempting to show a notched film to a friend a while ago, the film embarrassingly would not take up. I suspect that over time, the spring has lost its springiness and was no longer doing its job. I ended up making a non-springy thing to replace the actual spring, which served to lock the take-up pulley so there was no ratchet action. The only purpose this serves anyway is rewinding, which I tend not to do on projectors that are already worn enough as it is. I don’t have any springs that tiny anyway.