HX601 Contact Post Carbon Build Up

Chris Chapman

Active Member
May 25, 2006
Greenville, Michigan, United States
Frustration!!! I'm using HX601 (long life) lamps in my Altman Shakespeares. What I am seeing is carbon build up on the contact posts that prevent the lamp from getting a good contact in the base. Is there ANYWAY to prevent this carbon build up. I have posts that are cooking off before filaments do. I end up taking the file on my gerber and shaving the carbon build up off of the posts to ensure good contact. But every time I do that I make the contact post narrower too, so eventually I'm back in the same place where the posts are not making good contact in the bases.

Any thoughts?

(Yes, I've stopped using them and am back to the standard lamps, but I have, I kid you not, 30+ of these lamsp with good filaments and flaky contact posts. Kind of a waste to just dump them.)

Technical Director
Greenville Performing Arts Center


Senior Team
Senior Team
Premium Member
Nov 24, 2005
Saratoga Springs, NY
When was the last time you changed out the sockets in those fixtures? What usually happens is the contacts on the base start splaying and therefore the arching begins which causes the build up. Bases go bad a lot more then people think, and usually you can save a lot of money by changing out the bases periodically.


CB Mods
Premium Member
Jul 27, 2006
Portland, Or.
How old are the fixtures ? Typically, in the past, when I have had fixtures start with this behaviour, I simply replace the socket. Once the socket connectors loosen up there really isn't a fix accept replacing it. As you said to can take a needle file and get most of the carbon and oxidation off but without a tight hold on the lamp-posts it's just going to start the process all over again. Pretty soon your socket contacts are so thin they start melting, then it's "Katy bar the door", Dog and cats living together, We're talking Biblical destuction.
What's the price of socket replacement, compared to that ?


Well-Known Member
Apr 9, 2004
Franklin, TN
Yeah put some new bases in, and try to only put lamps with clean contacts in them. Any lamp you put in that arcs not only carbonizes the lamp, but the base as well. Also, some electro-sol on the lamp contacts may help a little, too.


Senior Team Emeritus
Premium Member
Mar 29, 2003
To sum it up,

It shouldn’t matter what lamp you are using, they will all go bad fast if your socket is bad. As a concept, a 120v/500w EHD lamp potentially could be running a bit cooler than a 115v HX-601 lamp but not by much. (Scrap the HX-601 lamps, go with GLA lamps not due to heat or quality, more for a refined smaller and more shock resistant filament.)

The nickel plating on the pins no matter what lamp it is will be the same and have problems do to poor contact no matter the type.

This poor contact to the lamp socket is potentially from two things. First as said, they stretch out with time. A socket that doesn’t hold to the pins tightly will form a higher resistance to the current passing thru it into the lamp. That resistance turns to heat and superheats not just the lamp but the lamp base and it’s wiring. If you open up the fixture lamp cap, the first ½" of wiring coming out of the lamp base has also melted down.

Second cause of heat can be from the above, or it could be from a bad lamp by way of pitting, welding or carbon build up inserted into a perfectly fine or even stretched out lamp base. Carbon doesn’t conduct well, nor does areas of pitting or mis-shapen blobs from welding to lamp bases. This all reduces the surface area of a pin that can conduct sufficiently. Lack of surface area in contact with the lamp or base is the key to heat above and here. That much current thru a small area than gets hot enough to weld the nickel plated copper of the lamp pin to the gold plated copper of the lamp base. Such a place that it’s been arching and or welding than further reduces the surface area that can conduct on the next lamp - it also often will cause similar welds on the next lamp installed. This or installation of a already welded lamp into a good lamp base will cause that perfectly fine lamp base to melt down in a similar way to the lamp.

On this size of lamp, there is little to nothing that you can do to save either lamp or lamp base. You can file them down some, could scrape the stuff off and provide a coating, but it’s still all about the surface area question, and now heat treating question added to it. Scrape a little coating off and it both won’t be as round in conducting in that area any longer nor be at the proper thickness for the heat dissipation. That mirror like finish or at least clean finish is what it needs to conduct, a scratch from scraping doesn’t touch and it won’t conduct even if it seems clean. This given a bit of carbon buildup is different than oxidation due to welding etc.

Commercial electrical contact cleaners can clean such things as long as they are non-residue leaving, than at that point some form of de-oxident would be a good idea for the pin or socket’s surface in re-heat treating it. This only for absolutely minor amounts of damage, after that, it’s probably only going to extend the life of the lamp/fixture a while and if one misses the damaged lamp base a second time around, you get back into the circle of constantly bad lamps.

On larger lamp pins & bases, yes, it’s feasible to service them especially with silicone abrasive Dremmel wheels that will leave behind a mirror finish - but only to an extent also. Larger pins also have a larger surface area overall so a bit of pitting and or areas that don’t contact will have less a role on reducing the surface area for high heat.

Key to all of this is to examine every lamp as you pull them from a lamp base. If the lamp looks bad at it’s contacts - you will find that the fixture lamp base is also bad. Don’t look, you often spend lots of money on lamps overheating and not reaching their expected life - if not filckering until the fixture stops working.

Curious today on the subject: our moving light repair department had a fixture come in for service out of a club in Kentucky. Tech people brought me a KSD 250/2 lamp from Devine lighting. Never heard of that company before, did some investigating and asked one of my distributers about them. He had seen some adds for them but was yet to hear much about their dependability. I was going to look into this lamp a little further and give both of us some info about the dependability of the lamps. Nothing on the website about the company history, all that’s known abot them is that first Amglo was making their lamps, now they come from China. In this case, who ever installed the lamp didn’t re-set the lamp counter so all that was known about the lamp was that the fixture now with a $250.00 service bill had just under a thousand hours of overall life on it, and this lamp had been installed somewhere before the 780 hours the last time the lamp counter was re-set at. Lamp I examined while it had a silvering of the globe problem, such a problem was probably caused by the heat and not lamp life. Electrode bubbling and or melting on the other hand showed a lamp that had been used for less than ten hours. Potentially with the below, this was not the first lamp installed backwards in the fixture.

Owner of the fixture sent it in presumably for warranty service on a still new fixture... sorry end results are that the customer installed the lamp backwards in the fixture and voided the warranty. This or they sent it in for professional service to change the lamp base as they probably should be given their ability to shove large pegs into small holes. One thing was for sure, this customer wouldn’t have much info about this new lamp type that would be dependable and informative beyond “dude...”

Normally I don't get involved with the moving light repair department stuff unless they need stuff like me and my SuperSawzall to rescue a HOG from a stripped bolt preventing it from opening up... (Ok, I spend a bit of time in that department once in a while in having a look at stuff.) Only thing that peeked my interst this time was the odd brand of lamp the rest followed having a look at the lamp than lamp base it fit into.

I matched up burnt pin with burnt socket and found that the small pin on the lamp was melted down, and the large hole in the socket was also all that was melted down.

Seems that the lighting technician who ever installed that lamp installed the lamp backwards. Even though the pins on the lamp are two different sizes so as to prevent installation backwards, this tech person no doubt forced the lamp into a “tight socket.” It’s presumed that the fixture and lamp were perfectly fine before the new lamp was installed backwards. Afterwards that lamp worked, the large pin in the small socket stretched it’s way into it’s base fine and will have had decent contact. The small pin in the large socket had just enough touching to work, but not enough that the small amount of surface area in contact didn’t overheat due to the current flow. Worked until it melted down sufficiently that it would no longer conduct.

Simple mistake, lamp forced in backwards cost between lamp, lamp base and service call around $250.00 plus shipping. Cause of the failure was a high resistance contact between the larger socket and smaller pin. This high resistance contact trashed the lamp and lamp base. Yep there was an expensive mistake.

On the part of our service department, they also learned a lesson, might be a simple and basic repair, but one still should look into the cause of the problem before just swapping out the obvious end result. Matching up burned pin on lamp to socket told of total operator error to which there would be no warranty, much less the tech person could be given a warning about installing lamps backwards. I on the other hand passed on the knowledge to one of our own moving light tech people so she could be aware that it's possible to install a MSD 250/2 type lamp backwards in the socket thus to be really careful as she is already in such things.
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