And more fascinating. While they are all G-9.5 lamps for
Leko's, for a
Fresnel, that is a lot of work so as to do such a change. Interested in what/how you did. Obviously the BTH lamp might have been a more simple solution for the 6" but very much curious in this work especially on the 8". That must have taken some work especially and above how the
socket holder for a
HPL was converted to
Fresnel slider plate use. Very curious in an admiring way - voided UL listing in a don't try it at home way, but very interested.
First let me say that my reasons for doing it were several. One of the strongest was that the
prefocus lamps tend to get stuck in in the
socket and make for a very difficult change of lamps when they are in the air, and just before a performance. Next, all of my
prefocus sockets were in really bad shape, and as long as I was going to replace them any way, I might just as well reduce the number of lamps that I have to keep in inventory, also we really like the color temp match to our source 4s.
The thing that made it less difficult than I might have supposed, is the use of the old discarded portions of the source 4 lamp burners that were pre 1998. You know the ones with out the lamp retaining spring. I have a milling machine and
lathe in my garage, and love to develop things using those machines. I did one
instrument first just to see if the
pattern was as bright and as symetrical as the original lamp. While the results were not perfect, they were so good that of the 10 or so people at our
theatre that I asked to compare the modified
unit with the original, only I could see the difference.
The first thing I did was to mill away all of the outer ring and it's supports of a early source 4
socket assembly. I had 32 of these pieces as I had modified all of our early (pre fall of 1997) source 4s with the upgrade kits, and had these parts sitting around. By machining away everything that was not part of the place where the
socket fits in and the two parts that run vertical to support the large
flat spring, that holds the
socket in and aligns the lamp, there wasn't a very large piece left. I did leave the hole where the
bolt is resessed into the
socket holder. I then fabricated a standoff from aluminum that had the correct height for placing the center of the
filament in the center of the
reflector. This standoff is sort of "C" shaped when viewed from the side. On the top where the
socket mounts, I machined it with a little notch so it would
line up with the
edge of the
socket holder and then monted it using the original hole for the
bolt, that was used to adjust the height position in the original source 4 mounting. This
bolt is set into the resess, through the top of my "c" bracket and fastened with a lock washer and
nut. The bottom of the bracket is drilled with several holes so that the original threaded holes that held the
prefocus socket could be used to mount the whole assembly. Again small machine bolts of the appropriate thread along with lock washers were used for mounting. Holes of a much larger size were drilled through the top of the bracket to allow a screwdriver to go through to mount the bolts. I used
TP22 sockets from
production advantage that are meant for the Source 4 PARs and PARNels. They will fit the older
socket holders, but are robust enough for a 750 lamp.
The fact that the newer Source fours with the retaining clips are so much better for keeping the pins of the lamps from loosening and arcing, I felt that I had to find a way of securing the lamps. On the two veritcal lamps supports of the
socket housing, there is a round portion on each. I drilled down into one of those posts and tapped it for 8-32 screws. I then got short stainless screws and washers that when screwed into those holes overlap enough to lock the top of the lamp
heat sink. After using them for a while, I went back and modified the washers using a dremel, so that the screw did not have to be removed all of the way. Just loosen a
bit and turn the washer so that it didn't
cover the lamp
heat sink. This made for a much more convenient lamp change.
As for voiding the UL listing, yes it does. In my case, the
theatre I volunteer at, had so many wiring issues that I corrected over the last few years, that when we approached the
AHJ, we demonstrated the mods and the advantages of less chance of a fire than with the
prefocus lamp sockets, where they can touch the mounting through a broken fiber
insulator, and the fact that we were removing all of the
asbestos wiring, that he was pleased as can be to support our use of the modified lighting instuments.
A
point of interest is that when I got around to doing the 6" Frenels, the steel spacer removed from the 8" fresnels was exactly the correct height for
filament placement on the 6" units, and saving me from fabricating spacers for the 6" Fresnels.
I considered taking pictures of all of the steps, but then realized that very few theatres could get the AHJs approval, and so decided that it was probably better that I not promote the idea. I just had a bunch of old Fresnels that were in really bad shape, and kept going out and were a pain in the --- to change lamps. It was a fun challenge, and they have been fantastic for the year and a half since I did them. I will say that the Electro-Control Fresnels, both 8" and 6", have a much better
reflector, and easier parts to work on than any of the Altmans.
Ship, if you are interested I will try and do some photos after the fact.
Tom Johnson