Vintage Lighting Radial Leko Lamp Socket Adaptors for Prop Lights

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Been working on adapting 1950's-1960's Radial Lekos, in 8", 6" and 4.1/2" size; to RGBW / LED lately for prop lights. Budget, Minimum as possible...

First prototype was doing it the proper way. A fairly inexpensive RGBW / LED node of medium power (didn’t even need the node lens accessory). Intent is to to glow the fixture lens brightly, not have real throw output on stage. Worked incredibly well!

Bent a steel bracket to mount to the lamp base assembly so the node would be mounted parallel to the lens and at filament center. Mounted the node, one resistor each and a second one in-line for the white (help from the electronics dpt.). Wired to a LED decoder and 12VDC power supply - both which fit inside the fixture body between reflector & shell. Amazing perfect output once bench focused, almost too much output in some light projecting on the wall. Had we mounted the more powerful node.... this fixture might have had some real punch in a servicable Leko type of way for under $200.00 in parts.

Four problems:
1) The step lens on the 8" Leko glowed with color, but was still projecting light. I’m also short on lenses at the moment & a lot of the fixtures I’m working on have broken or wrong lenses installed. No a 6" Fresnel lens is not a 6" step lens for instance... I replaced the lens with one side sand blasted polycarbonate.... Perfect but does not look as decorative. Later fixtures with lens trains won’t have step lenses, so its kind of a moot point.
2) The node got hot. It was properly mounted with thermal grease, but other than the bracket there was no real heat sink at the node. Sustained temperature at the node was 200F. This was close to the maximum temperature of the node & probably above the wiring maximum temperature. A 12v micro fan was added to the fixture, but the problem with a fan is it’s either going to be always on even if the LED is off (short of linking on the light board that 120v circuit), or tapped off the decoder which could be bad for the fan and cooling. Short of a thermal in-line switch also mounted to the fixture, if the fan were to stop working, the node could burn out. These fixtures will be installed in not very accessible areas & will probably never get serviced. A thermal switch would also allow the fixture to blink off and on which could get annoying.... not like anyone on-site would be available to repair the fixture should this start to happen & could be a long time before such a thing is reported.
3) Man/hours to do this was decent but too much for budget. LED node was cheap, but once you added in a power supply & decoder, resisters etc... Was probably in the range of $200.00 in parts.
4) My boss wants to keep the fixtures complete / historically accurate. Just wants to drop in a RGBW Marquee lamp on a pendant cord & leave the rest of the fixture alone. The theater is already getting their own museum of restored and accurate fixtures... why line use prop lights need to be accurate? (Remove the asbestos only). He is wavering on the polycarbonate lenses though.

Second prototype had me spend a few hours over a weekend grinding and sanding some ½" threaded rod so as to mount them into the G-38 fixture lamp socket, this to tape a pendant light lamp socket at the bench focus height of a incandescent 1500T24/6 lamp. I used the TMB RGBW G-16 medium based marquee light system in use all over the theater house already. Challenge is it’s only like 25 watts in luminous output. At least if bench focused, it might have a chance to compete with the above. With the step lens, the fixture had a slight glow of something, but unless directly looking down the fixture beam of light... almost no punch. Add the polycarbonate sand blasted lens, ok.. This could work, but was pre-production hack & not a solution for doing the 4.1/2" and 6" Leko’s... Boss also wanted to just stick in a pendant lamp socket with the lamp into the fixture.

Third Prototype removed the tape from the lamp socket - Knew he would want to see his idea done thus just taping the last one on. Stuck the lamp socket in just free hanging, spent some time attempting to at least center it on the reflector... Output as expected crap and almost zero with the step lens.

Fourth Prototype... If I’m removing the asbestos, I’m into the lamp socket anyway, why not re-store & re-wire the lamp base to work with the 24v marquee lights chosen? In the past I have made G-38 to E-26 lamp socket adaptors.... Even grabbed one, a Tri-tap 2x NEMA 1-15 to E-26 medium screw adaptor, and a lamp socket extender with the G-16 marquee lamp. Yep that bench focuses.

Made the CYX to A-19 lamp adaptor in the past.... why not make a 1500T24/6 to G-16 golf ball lamp adaptor? Out of lamp base parts, I had bad CYX lamp bases and bad shells to P-28s lamp sockets. Turns out a E-26 medium screw lamp socket will fit inside the porcelain shell of a P-28s lamp socket - so you can adjust the seat height up or down.

I made the lamp socket adaptors which will bench focus the G-16 lamp to a G-38 lamp base. I can now wire up the lamp socket properly & have a properly done fixture.

 

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For years now I have been thorizing doing something with the P-28s lamp socket. Primary was adapting from P-28s to G-9.5 for Radial Leko's, but also after many more years of adapting radial Leko’s to A-19 lamps, an adaptor for this which would just fit without modifications.

Got a step further in the first problem tonight, and mastered the second problem - this will work!

Theory.... A P-28s lamp base is 28mm in Dia. A E-26 lamp is 26mm in Dia. If I were able to remove the lamp base of a P-28s based lamp from the lamp, would a E-26 lamp screw fit into it?

It does!!! Specifically, if you use a 2-piece lamp socket extender (It’s E-26 screw threads are slightly longer than single piece extenders - very important.) You can screw the lamp socket extender into the P-28s base shell sufficiently that the center bean (hot) contact will stick out of the shell of the P-28s sufficient it will contact the center plate of a P-28s lamp base. Have to leave a slight gap between lamp socket adaptor porcelain and the shell of the P-28s lamp base or it will not 1/4 turn in.

The “How to” on either project, upon request.

So a single lamp socket extender, should work with doing a A-19 lamp in suitable height to bench focus on any radial Leko. (Philips Hue for the home with old Leko’s?) Have not tested this yet - but should be enough take up on the fixture bench focus to make this work if not close enough or dead on. Did line up adding a second lamp socket extender stacked atop the first lamp soecket extender and the G-16 TMB Marquee lamp will bench focus to a EGE lamp seat height.

This was also just like an hour of work - quick / easy. This will work. Got enough older bad GE lamps to make three of them. Just need to pull the lamps from the theater to hopefully get three more. The unfortunate key to doing this is the GE lamps (not sure if still done) have basically a dual lamp base - the P-28s shell, and a cup soldered inside it. Most other brands only directly cement the porcelain of the lamp directly to the P-28s base. This would be hard to remove in heating up and it pulling right off.

Shell of the P-28s now removable... potential for the eventual adaptor to G-9.5... a step closer.

More photo's coming as pictures download. Oh' Crap!!! one rolled off the table and broke. Luckily it was the outer removable part of the 2-piece lamp socket extender - easily replaced.

Of lamp socket extender's and lamp sockets in general, you want the non-glazed ones if you are using ceramic high temperature epoxy in glueing them together. The glazed two part lamp socket extender with it's longer threads was the only workable solution for the P-28s lamp socket in center contact. In photo's with this adaptor, the A-19 LED lamp was a bit longer, but should be able to be taken up with fixture bench focus. The G-16 lamp, almost spot on for bench focus seat height.

 

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P-28s to E-26 lamp socket adaptors part 2, Next round of them

The E-26 to E-26 lamp socket extender you want to use on this is a Leviton #78477 - it’s center hot contact sticks out a bit more than Westinghouse and other brands. Your center contact must stick out about 1/16" below the bottom of the P-28s shell installed. Other brands of lamp socket extender are fine for other types of adaptor such as a E-39 to E-26 adaptor with a lamp socket adaptor so as for vintage lights, convert from 1Kw globe lamp to 400wG/SP, or making a A-21 cyc into a A-19 cyc.

Only P-28s lamps with a inner metal shell soldered to the outer metal shell are at this point removable. It is possible with the same steps to remove the lamp socket shell from other types as a theory not tried. You will find older GE and Wiko lamps having this shell, not sure if they currently do this. Save your bad P-28s Leko & Fresnel lamps with the double metal shell, as with all bad CYX type G-38 base lamps & bad P-28s lamp socket bases if the porcelain is still good for future adaptors.

1- Remove the globe of the EGE etc. P-28s lamp or it might explode while heating the lamp base. Safety gear and a carpenter’s framing hammer inside a trash can. Or better yet, a 10gal. Drop can or metal paint bucket once sealed & dropped will implode the even bad lamp glass capsule safely. Even a bad lamp can still be pressurized & send sharp glass flying, do it safely. Don’t throw the lamp at a brick wall - could damage the base. Cut off flush to base any monofoil or lead in wires from base to filament.

2- Remove the center contact bean/plate or solder blob from the bottom of the lamp. Easier if done before the globe is removed in holding.... but possible the lamp could break while sanding. Corse paper belt sander or grinder with sanding flap wheel will make quick work of the plate. Can also reverse it to sand flat anything left from the lead in wires.

3- Scratch Awl/Cold Chisel/Screw Driver... break free the epoxy at the bottom of the lamp’s socket. This is the insulator between the center contact and the outer shell to remove. Unless you break this up, the other shell won’t easily free up from the center lead in wire also glued to it by way of the epoxy. Should break away almost like glass or soft rock in not being dangerous to just pound out in breaking. There is usually an air gap between the epoxy at the bottom and any upper shaft part of the lamp making it easy to break apart.

4- Turn on the MAP Gas torch, adjust to hot setting. Heat the outer shell evenly - might have to get it hot - but normally not so hot it glows if you can find the solder between the sockets. That neutral lead in wire or shell to shell should be soldered at only one point, once heated up enough... you should be able to pull the outer shell free. Only one out of ten so far would not pull free. Be careful not to over heat, might seem some light fire inside the shell (don’t worry), might be a trial and try again thing to do. Many styles out there, some outer shells pull off easily, others take some twisting off especially if they have a peened connection to the inner shell making it more difficult. Patience and not over heating but looking at what the problems are wins the day... Than there is those that just come right off. Let cool all removed parts. (Some elder EGE style lamp porcelain standoffs could make interesting and decorative X-Mass Tree ornaments once the center cement is chipped out.)

5- Once the P-28s shells are cool enough, don’t worry about what the outside of the shell looks like, worry about the inside surface. This will both have to seat with very close tolerances into a E-26 screw base neutral shell and conduct. Especially if the lamp base P-28s was peened in connecting better to the inner metal shell, you will need to grind from the inside this flat again or it will be really hard to mount on the E-26 base level. Dremmel grind away in making the peen flush. Grind off any left over solder also.
Once you have the inside shell basically flush from any solder sticking out, or peens... switch to the brass wire wheel and clean - it needs to conduct and accept new solder. Let cool.

6- Dry fit P-28s shell onto the E-26 lamp socket adaptor. Should easily screw in most of the way without tools. If it doesn’t you have found a slightly smaller than P-28s in ID shell. Switch the Dremmel to a sanding wheel and start removing some of the top of the E-26 lamp socket adaptor screw threads in making smaller OD to them, but before this make sure the P-28s lamp shell is round and removed of stuff sticking out. Sanding and testing, than sanding more best method as with sanding equally deep all about all the threads.

7- Roll on a 3/4" silicone O-Ring of 1/8" wall or better yet 5/32" silicone O-Ring with the same ID. This O-Ring will become a spacer in seat height between the flare of the ceramic of the E-26s lamp base adaptor, and the P-28s shell. Remember, your P-28s medium pre-focus lamp socket must still seat in a P-28s lamp base socket - so there needs to be a bit of a gap so as to 1/4 turn the adaptor into it’s base.
This O-Ring will also come in handy as a seal later during the epoxy step.

8- Seat the P-28s shell all the way down on the E-26 lamp extender screw. Ensure that the hot’ tip of the center mount extends about 1/16" past the bottom of the shell. Might take some screwing down, or just pushing. Might be some difficult screwing down all the way seated. Klien conduit pliers work well for this as with above processes. Center pin must stick out by about 1/16" or remove and review steps. If only slightly off, you can peen in a little bit the top of the shell - the above pliers are about the correct weight in not doing too much. Base might seat better, could with hammering on the pliers it seats better etc. Just don’t roll over the base of the P-28s shell too much.

9- Ensure this fitting will fit in a P-28s lamp socket. Don’t put it in all the way in locking down, just check your round insertion fitting. Adjust the brass shell of the P-28s shell as needed (conduit pliers). This will be the last time you can test this, so do so before going forward.

10- Heat up that MAP gas torch again. This time instead of heating up the outer shell, you need to heat up the inside part of the shell and lamp socket adaptor. Need to solder the screw threads in at least a few points to the outer P-28s shell for electrical and mechanical needs. This is the hardest part of the process to do correctly. Even with practice, might be cold solders - the need for more than one contact point as opposed to over-heating an area... Experience in sweating water piping, good, but screw shell to P-28s shell more difficult given dissimlar materials. (Leviton base is different than that of the P-28s shell.) The solder needs to suck in and sometimes waiting a moment with heat will do it, but don’t wait long before trying again.

I use 0.093" Lead free rosin core. Could be many ways to do this better, but you need to see the solder suck in & bulk size of solder will help I think as long as hot enough. I chase that hot enough to suck in for this.

11- Once you have good connection of P-28s lamp socket to screw shell, the rest is easy. Let cool. Perhaps swipe some of the child’s Play Dooh in further sealing up the silicone O-Ring, because the epoxy is coming and will probably seep thru any gaps in that O-Ring in needing more epoxy before it cures.

12- Epoxy for more support and seal up the shell base. Lord #310A/B Structral Epoxy Adhesive, High Temp. 1.69oz. McMaster Carr #66195a13 is the best of medium/high temperature epoxies I found. Need the 74695a12 mixing straw. Seal up flush to the rim of the P-28s your work.

 

[DELO72]

That's impressive. Well done sir!