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LAMP CONVERSIONS

Baby Lamp Adapter

Changing the lamp and power supply can be OK if done sympathetically. By this I mean try to do a lamp conversion that retains the same outward appearance and could be restored to original. I think the ideal way is to make a unit that fits in the existing lampholder, eg smash up an old, defunct lamp and fix things to its base to support a new lamp. This way you use the original circuitry, too. I have actually managed to make a unit that fits into a Baby lampholder and takes a tungsten halogen lamp. 6v 10&20W and 12v ditto will all fit. It relies on me having found a small batch of tiny holders for these small lamps, and some fiddly work. OK, OK, I’ll go and do a picture, just talk amongst yourselves for a bit.

The lampholder is a neat push fit into a bit of standard brass tube, which in turn is ditto into a Baby lamp socket. What I do is to cut one wire off completely and shave one side of the lampholder to just expose the outside of the contact. A blob of solder on this, carefully filed to the exact height, makes a good contact with the side of the brass tube. The other lead is cut off short and soldered to a very short length of thin screwed rod (studding). This is just long enough to pass thru the small circular insulating bush shown here, and is held in place by a nut, forming the second contact. I usually solder over this a bit to help stop it undoing. Voila! It works best in later Babies where there is a screw to retain the lamp, but it will work as just a push fit. I am working on the assumption that the small exposed area of plastic is not going to get hot enough to melt! Now, if anyone can find a source of these little lampholders, we’re in business. (Now found a new batch, so if anyone needs one made.... for a fee, of course.)

9.5mm Vox

I have for a long time wanted to make a tungsten halogen lamp converter for the Vox that does not involve changing the projector in any way. Past conversions I have done or seen mount the lamp in the side of the inner lamphouse, burning sideways. I reckon if a halogen lamp can burn sideways, it might just as well burn upside down. This is bound to shorten its life, but the lamps are a bit more readily available than Vox lamps. I have tried in the past to make up a ring with pins like the Vox lamp pins, but have always found this too tricky for my capabilities. I have therefore adopted a slightly modified approach as shown in the pic. An aluminium disc about 41mm diameter and 2 or 3mm thick sits neatly just above where the Vox lamp would sit, where there is a convenient (insulated) "step" in the lamphouse. The lamp is suspended from this by two bolts. These in turn attach to a separate little unit made up from a washer drilled for the lampholder and the support bolts, with spacers to get the lamp down as far as is needed. There is fine adjustment of the lamp position heightwise by moving the nuts on the support bolts (either side of the washer) up or down. Electrical connection is made first by a bit of bent brass strip screwed to the alu disc and bent down thru a slot in the side of the disc. This sits into one of the holes the Vox lamp pins use and the bolt also secures the first lamp lead. The second connection is thru the insulated rod, which is threaded at one end and so bolted to the alu disc. The other end is drilled for a short brass rod, with a threaded hole part way down matching a hole on the side of the insulated rod. A screw connection can then be made to the second lamp lead. The brass rod protrudes thru the top of the insulated rod to connect to the contact in the lamp cap.

It all sounds OK, but this job nearly drove me crazy. The main reason is that whatever idiots designed the lamp base set the lamp pin sockets at a weird angle to the holes I use for screw mounting - you can see this in the separate lamp base I have put in the picture above. My first approach was to use brass rods with a screw thread at each end, directly bolted to the lamp base. This ought to work, but..... The filament in the Vox lamp is suspended from to rods which are bent to move the filament closer to the condenser lens. I found I couldn't get away with straight rods moved further across as they then fouled the bore of the top section of the lamphouse and also the heat shutter mechanism. So I tried using bent rods. However, because the fixing holes and the lamp pin sockets are at that weird angle, one rod has to behind the other where they attach to the disc in order to get the filament square to the condenser. This seems to mean that the rods cannot be identical, 'cos I tried and failed. I could not figure out how to make the second rod the right size. In the end, I came up with the design I have described, which seems to overcome most of the problems, but it took me a lot of trial and far more error to find exactly where the holes for the support rods needed to be in the alu disc. I was homicidal by the time I finished, but at least I now have something I can simply copy.

Here is a new one - it's mostly borrowed from the old one, but you can see the lamp supports are much more offset, and the support ring is now like the ring on a Vox lamp. This means the thing sits lower in the lamphouse so I had to extend the top contact a bit. It does work, too. There is however a strange quirk; sometimes the pilot light operates at reduced output and then the main lamp doesn't work. It seems to be a matter of the top contact, but if so, the implication may be that the wiring provides for pre-heating of the lamp, something I have not come across before and will need to investigate further.

Here are a couple more examples, one for the Super Vox (we don't care about burning QI lamps upside down or sideways, do we?) and another for any medium pre-focus machine. OK, so they're maybe a bit crude, but it would no doubt be possible to make it neater but, hey, it's out of sight and fulfils the main criterion; it doesn't change the projector. Incidentally, does anyone know why the commercially available holders for QI lamps are huge, cumbersome and downright unhelpful, eg by having the fixing holes at a strange angle to the lamp pins? There must be a better way - has anyone anything to offer about DIY bases?

Pathescope H                

Here is a prototype lamp conversion. It uses a lampholder which says on the packet it's for an A1/259, but it seems to accept a 12v 100w. The lampholder has some tiny holes in, which take a 12BA bolt. I drilled and tapped a couple of holes for these. Then the wires have to pass out thru holes drilled below the mirror, or you can't get the base to the right position, and thru again to connect underneath. It should now be possible to fit the original lamp wires over the lampholder wires. As you know, I'm not keen on permanent changes to projectors, but even tho' I've made some new holes, there is nothing here to prevent reverting to the original lamp. Actually, looking from a different angle for these pix, I think I shall have to raise the lampholder a bit to get the filament central.

 I next turned my attention to the lamp. I was not really happy with the one shown above, as it used a base that meant the lamp was  a bit of a force fit  - not ideal. I started out down the same line, but then changed to this pattern. I used the small (10 BA) tapped holes I had already made, but you could go larger, of course. I just used a thin bit of alu that was lying on my bench; it was more hole than metal when I'd finished. I needed spacers to get the lamp filament to the right height. The wires just go straight thru the lamp socket to the terminals beneath.

200B

I felt it was time I got a bit more computerised on the sketching front. I have done two versions of a drawing for a 200B lamp adapter, tho'  the computerised one didn't want to appear on site - I had to scan it in from a print! B************ format incompatibility I expect.

Pathé Lux

I have been getting in touch with my inner Lux, starting with a lamp conversion. You know how I prefer to leave projectors in their original state, or returnable thereto. These pix show how I've tackled this with the Lux.

Removing the spring-loaded lamp retainer (pic 1) leaves two holes (already tapped M6 x 0.6, not the normal M6 thread - I had to make screws) in the bottom of the lamphouse, and there are already slots at the base of both inner and outer lamphouse covers. In pic 2, you can see that a thick piece of Tufnol has been drilled to fit these two screw holes, with a hole to go round the upstanding part of the original lampholder, a cut-out to avoid blocking cooling air from the motor fan and a notch to allow the lamp wires to pass thru the slots in the lamphouse covers. The lamp is mounted on a sheet of aluminium with two M2 screws into tapped holes. A slotted hole provides for fore and aft adjustment of the lamp - height and side-to-side can be set in advance, but not fore and aft so easily. The alu sheet is held down by just a single screw thru the slot and thru the Tufnol (I didn't need to counter-sink the Tufnol hole, but I was making this all up on the fly). It seems adequately secure. I couldn't use the other hole in the same way as there is virtually no space between the hole and the inner lamphouse cover, and anyway it would block ventilation from the motor fan.

In pic 3, the lump of alu which I bored out to take the figure-of-eight socket is deep enough to allow the wires to be fed thru their holes and soldered to the terminals, then covered by some thin Tufnol. This block will then fit onto the outer lamphouse cover, with screws passing thru the alu block, thru the vertical slots in the lamphouse cover, into a metal strip with two tapped holes. This is the same idea as one of the fixings for the ammeter. The entire unit as seen here can be removed just by undoing a few screws. Replace the lamp retainer and the machine is back to original. No need to change the original wiring at all. I plan an  external power supply - one of those modern low-voltage lighting transformers - with a switch in its mains lead, powering a 12v 50w lamp, which will hopefully not damage still frames. With a bit of black paint, the conversion won't be invisible but relatively unobtrusive. Here are more pix showing the original lamp retainer in place and various views of the conversion. In pic 3 below you can just see the threaded strip between the two lamphouse covers.

KOK 28mm

I've been fiddling with a lamp conversion for a Pathé 28mm KOK, using a ceramic lampholder which will take 12v 35 -100w lamps and maybe higher wattage.

Pic 1 shows the KOK lamphouse "cap" which slides onto the front part of the lamphouse, which is fixed to the projector. (This is a "mains" model; no dynamo, smaller crank handle and  smaller pulley wheel at the rear). The lampholder is incorporated into the cap. The bit on the right screws into the tube in the cap and incorporates a spring-loaded lower contact. This part is not used in this conversion.

There is very little room to do anything; getting the lamp at the right height is hard enough. As usual, I was constrained by my desire to avoid any changes to the original. I made the holder unit to fit into the existing tube from the top, just as a lamp would be inserted; this enforced considerable miniaturisation. The unit is a force fit, basically wedged in rather then fixed with screws or whatever.  In pic 3, you can see a short piece of brass rod, about 8mm in diameter. This has two thru holes which take the wires from the ceramic holder. One of these wires is cut off short, with the end stripped and folded over so that it wedges into its hole. This provides a contact thru to the terminal on the side of the lamphouse cap. Because the rod is smaller than the ceramic holder, the wires don't fit neatly and the ceramic holder flops about. This is therefore fixed in place with Araldite, so that the holder and brass rod are permanently joined and not floppy.

A third hole is drilled and tapped into the lower end of the brass rod. A screw (with its head much reduced in diameter) passed thru the teflon rod  (see pic 4) and fixes it it to the brass rod. Another hole allows the second wire from the the ceramic holder to pass thru. As for the brass rod, a third hole is drilled and tapped into the lower end of the teflon rod. The wire connecting to the power supply, and the end of the second wire from the ceramic holder, are soldered into rough loops. A nylon screw then passes thru the two lops, thru a small spacer and into the threaded hole in the teflon rod. This keeps everything insulated. In practise, it's easier to fit the unit into the cap if the nylon screw is first removed, but that's not a major problem. The aluminium sleeve has a grub screw which grips onto the brass rod; this allows a bit of up/down adjustment. Unfortunately, the unit has to be removed to get at the grub screw.