P28S and BTR, Out of the Box Thinking

[Ken Johnson]

Ladies and Gentlemen,

As you may tell, I am new to this forum. In my searches of the last two weeks, I believe that you may be the only ones able to help me.

First of all, I am a retired telecommunications engineer. In college, I minored in technical theater and was trained in lighting, lighting design, set design and construction. Much of my early career was spent in
television engineering with much of that in maintenance and maintenance supervision. Working with studio lighting and repairing instruments was all part of the job.

This leads me to today. I have volunteered in the theater of the local community college for the last several years. About three years ago, they underwent a major renovation. As part of the contract, new instruments were provided. One particular instrument is giving them problems. It is an Altman 1KAF-MPF 6” fresnel. The instrument itself appears to be fine, it is the P28S socket for the 1KW BTR lamp that is giving them no end of trouble.

This is what brings me to you. Yours is the only site I have found that addresses the burning and arcing problems they are experiencing.

Last week, as we were hanging instruments for a show, two more failed. The lamps exhibited bad burns and signs of extensive arcing around the center terminal. The socket center contact was very badly burned, pitted and discolored to the point that it looks rusty. The rest of the interior was heavily blued from heat and the 250 degrees C rated insulation to the center terminal was melted and pealed back a good inch or more.

Many of you have seen this and it is nothing new. I know that at least one of your members has had good luck cleaning and resurfacing the P28S sockets, but that is not why I am writing.

I am going to go outside of the box with an observation of the socket and the base of the BTR. Please be patient with me.

A new P28S has a conical depression machined into the center of the center contact. It's purpose appears to center the small ball (I have heard people call it a 'BB') in the center terminal of the BTR base and provide a sound contact between the two. With a brand new socket and a brand new lamp, the 'BB' will seat in the cone and make a contact all the way around the 'BB' where it completely touches the cone.

This sounds like a good idea, but I am beginning to wonder how well it holds up in service.

A 1KW lamp will draw about 8.3 amps in a 120v system. This arrangement pushes all this current through the ring shaped contact point between the socket and the lamp. The elements of this ring are hard metal. I am guessing that the socket is nickel and the lamp contact is brass. This ring shaped contact patch is very narrow.

My concern is that this appears to be a very fragile arrangement. Any corrosion at this junction will reduce the contact area and rapidly increase the heat generated at the junction as current is forced to flow through a smaller contact area. If the two surfaces are not perfectly round and perfectly mated, you will have a reduced contact area and more heat again.

Alright, here is where I climb out of the box. Many years ago, I remember the 1KW lamps we used in the scoops in the TV studio. These lamps had substantial contacts in their bases and we had few problems with them. I just looked at a 60W lamp in a light in my house and it has a much larger contact area than a BTR.

I am thinking of a way to greatly increase the contact area between the BTR base and the P28S socket. Looking at the base of the lamp, it actually looks like it is designed with my idea in mind. The 'BB' sits in the middle of a flat ceramic plateau about 9mm in diameter. I just got back from the hardware store with a package of brass #8 flat washers. This washer fits snugly around the 'BB' terminal and still rests flat on top of the ceramic plateau. I am thinking of carefully soldering the washer to the 'BB'. Not a lot of solder and none in the contact area of the socket center terminal. A dry fit with the P28S shows that it sits there perfectly and gives a much larger contact area.

Alright, that is the thought. The college is really short of funds and I have already purchased two new sockets and the necessary hardware and tools to install them. (Thank you to one of your members for the materials list.) So this is coming out of my pocket. Members of this forum are going to forget more about stage lighting that I will ever know, but sometimes out of the box thinking can solve a problem. I would like to hear from you, I need your thoughts. You may think of something I completely missed. If I do not hear anything, I will try one instrument and one lamp and put it into service. If it fails, no problem, I payed for it. If it works, we may all benefit. Either way, I will report back here.

Respectfully,
Ken

 

[Les]

@ship is really the guy you want to hear from regarding lamps (I believe it was him you were referring to in having good results with resurfacing). One thing I wonder is if all med. prefocus lamps have this BB. Seems like I always saw them with more of a rounded solder blob on the lamp contacts -- of course that could've been ten years ago. We also have a lamp supplier rep here (Osram Sylvania) by the name of @DELO72. I'll bet he could advise on this as well.

It would be worthwhile to call Altman and probably also your lamp supplier. Surely if it is a widespread case they will either have a solution or want to come up with a solution. Those sockets should last quite a long time under most conditions.

As for modifying the sockets, I think it would work electrically, but there is a bit of liability and the fact that lamp replacement would take a lot longer than it really should. Aside from treating the symptom rather than the disease, it might also compromise the UL certification of whichever fixtures you use them in. I don't recommend it.

I feel your pain though -- I am currently helping out an elementary school by upgrading their lighting system from 4 units to 20. Some of it is coming out of my own pocket, but I have been shown an unusual amount of generosity lately so this is my way of paying it forward.

Edit: While you're investigating, take a close look at the BTH lamp for your fresnels. This website had a lot to do with its development!

 

[ship]

A new P28S has a conical depression machined into the center of the center contact. It's purpose appears to center the small ball (I have heard people
it a 'BB') in the center terminal of the BTR base and provide a sound contact between the two. With a brand new socket and a brand new lamp, the 'BB' will seat in the cone and make a contact all the way around the 'BB' where it completely touches the cone.

This sounds like a good idea, but I am beginning to wonder how well it holds up in service.

My concern is that this appears to be a very fragile arrangement. Any corrosion at this junction will reduce the contact area and rapidly increase the heat generated at the junction as
is forced to flow through a smaller contact area. If the two surfaces are not perfectly round and perfectly mated, you will have a reduced contact area and more heat again.
I am thinking of a way to greatly increase the contact area between the BTR
and the P28S socket. Looking at the base of the lamp, it actually looks like it is designed with my idea in mind. The 'BB' sits in the middle of a flat ceramic plateau about 9mm in diameter. I just got back from the hardware store with a package of brass #8 flat washers. This washer fits snugly around the 'BB' terminal and still rests flat on top of the ceramic plateau. I am thinking of carefully soldering the washer to the 'BB'. Not a lot of solder and none in the contact area of the socket center terminal. A dry fit with the P28S shows that it sits there perfectly and gives a much larger contact area.

Welcome to the forum, I have one of those Fresnels called "Old Rover" in other problems with it you will find answers to with a search.
Never suck up to anyone - that makes us suspicious as it would you in being so complemented. The forum is filled with people just as curious and tech wear the jump jeans as similar to you. Your questions are just as valid as any we also have asked over the years and perhaps your asking this time such a question might be answered or discussed. Never give up the questions - any questions. I also wondered about these questions about pin verses plate at one time or another but never asked. I would suspect the pin or ball connection sticks down a bit lower for tension on the base spring, but a really good question overall. Mark from Osram/Sylvania will on this question chime in soon. He would really know the answer in presenting it not persay in a company why we do it this way way. Instead I would hope he knows the answer to bean verses plate contact.
HPR Controllbooth, Mark and I are linked to and are all intrested in problems about also.
The lamp probably isn’t the problem it would seem, any time you put a perfectly good lamp into a perfectly bad socket, it will fal sooner. Replace or resurface the socket? You already know about corrosion and as an electrical engineer in the study of, what problems. You now see more to learn about.

 

[ship]

I also feel the pain of paying it forward. Les let me know off line what you need, I might have surplus parts to send you.

Lamp sockets wear out and isn't a UL thing if listed for it. Modifying sockets that is a great question of liability of re-surfacing a lamp socket verses having to just replace it with a new one. So much over the years centered on having a bad socket and how to fix it I don't believe any discussion about necessity to just toss out the old lamp sockets and replace them with new. Very valid point.

 

[derekleffew]

One thing I wonder is if all med. prefocus lamps have this BB. Seems like I always saw them with more of a rounded solder blob on the lamp contacts -- of course that could've been ten years ago.

New ones do, old ones didn't.

Seems we've had this talk before, http://www.controlbooth.com/threads/radial-altman-porcelains.30471/#post-270126 and the following post.

 

[Ken Johnson]

I did contact Altman and they are not aware of the problem. One of their technical reps contacted me the next day, but was unable to provide any suggestions that might help. I realize that Altman does not manufacture either the sockets or the lamps.

Thank you ship, we are aware that putting a good lamp in a bad socket will lead to increased lamp failure. Also, bad lamps go right into the trash. Unfortunately, there may be a number of questionable sockets still in service. We are working on identifying them. We have 24 of these instruments.

I am not blaming the lamps, I know we have bad sockets. New sockets and new lamps work fine. My concern is that the design of the lamp contact (BB) and the socket cone depends on both contacts being clean and perfect. Any less and the current is forced to travel through a smaller contact area creating additional heat and eventually leading to failure.

There seems to be some confusion about what I propose. I propose modifying the lamp NOT the socket. I think my idea will greatly increase the contact area for the center terminal. Our lamps are made by Osram. Their bases are slightly different from the Phillips EGG shown in the above post. If you look at the base of an Osram BTR, you can see that a flat washer would comfortably sit on the ceramic ring around the center terminal. This washer would then contact the flat surface of the socket center terminal. However, these mating surfaces may still contain come irregularities hampering a good connection. I have thought of applying a thin layer of solder to the face of the brass washer. Installing the lamp will rub that against the socket terminal much the same way the solder blobs on bases did on the lamps I used many years ago.

The engineer in me has found what I consider to be a potential weakness and I am looking for a solution. I may be wasting my time, but I think I will try this on one instrument. I am just trying to help some really nice people who are short on resources. If this can reduce a problem for them, it is worth it.

 

[Les]

There seems to be some confusion about what I propose. I propose modifying the lamp NOT the socket. .......If this can reduce a problem for them, it is worth it.

Sorry - I misspoke in my first reply. I do understand that you plan on modifying the lamps. My original intent still stands as related to liability as the lamp/socket combo is part of a UL Listed assembly and modifying such will compromise that listing. I do think your intentions are in the right place, but know that this modification would have to be done for every lamp change. How long do you plan on being available and do you really think the modifications would continue to be done correctly, safely, or at all after you leave?

I really hope Mark from Osram chimes in. I think he would be a great resource for you.

 

[gafftapegreenia]

I have been making noise about this for years, and it is reassuring to know that I am not the only one who has identified the problem. The old medium pre focus sockets had a flat contact, and the old medium pre focus lamps had a nice huge blob of solder on the bottom. This was great! Now, that stupid BB and the cup contacts almost guarantee failure. I love Fresnels, and many instruments that use medium pre focus sockets, but with the current sockets its just not worth spending the money.

Now, I have successfully converted a crop of 65Q fresnels to medium bi post lamps, but that process was tedious, and likely voided the UL warranty. The 1KAF DOES have a medium bi post option from Altman, so you may have more luck with that.

I will admit that I have ground down the cup shape contacts to a flat surface, and that helped tremendously, but it still probably voids the UL listing.

So, in short, either live with voiding the original UL listing to make fixtures work as they should, convert them to a non medium pre focus socket, or lay them to rest. It angers me that this is so but no one with the power to do something about this problem really seems to care.

 

[ship]

Mark from Osram will be my captive audience in a visit on Tuesday. I will bring this up. Good points in I'm not sure where I sit on bean pressure verses blob concact surface area. Good debate I have thought about in the past but don't much use such lamps these days in a problem.

One notes brass corrodes so that's a non-seller thing for needing a coating but also the solder blob isn't really anything respectable for contact either.

My daughter - a princess of course could attest to the problems or a beam in the bead.

 

[derekleffew]

but also the solder blob isn't really anything respectable for contact either.

We're probably mis-charaterizing it as a "solder blob"--it may be molten metal (perhap nickel?, or an alloy?) but was a process of the manufacture of these types of lamps from the 1930s until early this century.

But I agree that a user adding his own lead-free, rosin-core electronic solder to a contact (in either the socket or the lamp base) is a bad, bad idea.
-----

My daughter - a princess of course could attest to the problems of a bead in the bed.

Indeed, I've heard the legend that little Renette can detect a beebee under a stack of mattresses thirty feet tall. Pity the poor fool who attempts to woo her, given her father.

 

[ship]

We're probably mis-charaterizing it as a "solder blob"--it may be molten metal (perhap nickel?, or an alloy?) but was a process of the manufacture of these types of lamps from the 1930s until early this century.

But I agree that a user adding his own lead-free, rosin-core electronic solder to a contact (in either the socket or the lamp base) is a bad, bad idea.
-----
Indeed, I've heard the legend that little Renette can detect a beebee under a stack of mattresses thirty feet tall. Pity the poor fool who attempts to woo her, given her father.

got the joke

On the contact point of a P-28s lamp, what specifically are people looking for? A combination of the convex plate below the lamp with say a nickel plating to it or a ever so slightly longer plated ferrule / bean so it has a little more pressure on the base in exchange for some slightly less surface area? Or other thoughts? Can't really be a flat plate at the base of the lamp for contact I think.

Sent most of my old lamps to work last week for a new old lamp display but found others to phot tonight.

In the photos are old Westinghouse and Radiant solder plates that sort of melted to contact best but were never really a good design on T-20 incandescent lamps. Literally the contact was a blob of solder and it often glued itself to the socket. Next a Sylvania EGE lamp with a solid ?copper plate and a lot of corrosion and arching from a bad base. After that one Philips BTL with the bean but it seems like it's a little more flattened on the bottom - this before I silicone fiber wheeled it's arching off. Interesting corrosion on it - probably from a water logged fixture. Last a Philips EGE, almost looks new, round base, center of it is blacknd because it's only a little bit of surface area contacting this base plate but the same distance to the locking fins.

While surface areas on medium pre-focus lamps are totally resurfacable in about a 90% saved way, the springs wear out, and if any pitting is in around where that center bean has been located or a concave area starts to develop with pitting, it means less surface area of contact no matter the tension. (Beyond screw terminal problems at times at the underside - brand specific in fixable or not.) For my tastes, I would prefer a slightly flattened dish plate which is heat treated. Or perhaps a flattened bean/ferrule center contact that gives a concave but basically flat impression. That and the contact area to locking fin distance just slightly longer.

Notes for Mark/Osram.. Bryant, GE and others used to make P-28s lamp sockets that were interchangeable. Same OD of the porcelain and same mounting holes. Most Leviton and other brands still making the socket these days are larger in not being the same. A bit of a challenge to re-mount a modern lamp socket onto an old fixture and on a radial Leko the larger OD is a problem. This much less aligning mounting holes for someone that isn't experienced with doing so by way of making new holes. A bring back and upgrade of the "classic" P-28s lamp socket specs would be best for the industry. I know I stockpile my old design lamp sockets and replace modern where I can at this point. Bryant screws on the wire connection side are not removable which makes it hard to clean up and replace contacts. Many styles of the classic socket over the years. Even found some brands where the center contact to the lamp base was removable and I could replace the center spring.

But as above, smaller dimishing market for old Fresnels and lamp sockets. A few months ago I had a demo from Ushio on a LED Fresnel that was totally cool. Not something bought but completely in mind for the future. LED will probably be the way the future and will be coming down in prices lowering and technology advancing. In phone call today from Mark from Osram he is looking into these questions of the bean lamps, will chat with the factory. Also a side note... look into the BTH if you want your Fresnels to match the Leko's in color temp.

But overall, I don't much use such lamps where I work these days, I just resurface and museum put them. In a re-design of a BTL or BTH, what do others think on a re-design of it? It's not a classic design for how the contact was done as I have presented at least three or four versions in the photos. I would think somewhere like a more flattened dish, though a flattened bean is also good. Extend the length of that center contact ever so slightly to compensate for weaker springs or damaged bases? My thoughts at least on discussion. Anyone else have problems with modern lamp sockets as replacement?

 

[Ken Johnson]

Here is an update.

Using an old lamp for practice, I soldered a brass washer to the base and appear to have made a good contact. However, looking at it, I do not think this is a viable solution. Les pointed out in an earlier posting asking what happens when I leave the college. Can they be expected to carry on? The answer has to be no.

Alright, so what is the next plan?

I was at the college today and opened a new case of Osram BTR lamps. I wanted to see what a new contact looked like. When I opened the first box, I decided to open a second box just to be sure of what I found. The center contact 'BB' was not nice and smooth so that it could make a full circular contact with the P28S base. It was rough textured to the point that I have to question how good an electrical contact it can make. Especially a contact that will conduct over 8 amps without overheating or arcing.

So, what do I do now? Getting in there with fine grit sandpaper trying to smooth out the contact will be a lot of work with no guarantee of success. If I do not keep the surface nice and round to mate up with the socket, I may not have gained much of anything. If I remember correctly, I saw a posting where ship talked about cleaning up bad contacts on lamps. Maybe I need to re-read that.

Any experience here would be greatly appreciated.

Ken

 

[Les]

My advice is to keep bugging the lamp manufacturer. One should not be expected to perform remedial action on their lamps prior to even the first use.

 

[gafftapegreenia]

My advice is to keep bugging the lamp manufacturer. One should not be expected to perform remedial action on their lamps prior to even the first use.

I need to start a letter writing campaign. Complaining for years on CB clearly hasn't worked. I've even mentioned this to @DELO72 a few times at USITT.

The lamp is part of the problem, but the new BB design works alright with the older flat center contact. Its that new !@#%*$%$% cup shape contact that is eating lamps. I wish Bryant was still making that socket.

 

[Ken Johnson]

In a recent post, I talked about problems our community college theater is having with their BTR lamps in the P28S socket. In a nutshell, short life and arcing in sockets and lamp bases. I was attempting to improve the contact between the center terminal of the lamp, sometimes called a "BB" and the socket to reduce contact problems which I assume is causing much of their problem.

I am only a volunteer here. My background includes college training in technical theater including lighting, but I worked for many years in broadcast television engineering. Most of that in maintenance which included studio lighting instruments.

I had seen many of the failed lamps, but had not looked closely at a new one. Yesterday, I opened a new case of Osram BTR lamps. I wanted to look at the center terminal "BB". What I found caused me to open a second box. The "BB" was not bright and smooth as I would expect for a good electrical contact. It was rough to the touch with considerable texture to the surface. In my long years of experience working in electronics, this is NOT how you make a good connection.

Okay, here is what I am asking from the community. If you use lamps like the BTR, BTN, BTH, BTL or any that use the P28S Medium Pre-Focus Base, would you please look at the base of a new lamp and inspect that center contact "BB". Is it smooth and bright or is it dull and rough. If you find smooth and bright, please let me know what model lamp and the manufacturer and whether is was recently purchased.

My research has found BTRs marketed by Osram, Ushio, GE and Eiko. There may be others.

Your experience with these lamps would be appreciated. I hope we can find a better source for our lamps.

Thank You,

Ken

 

[Ken Johnson]

Another update.

After yesterdays discovery of rough contacts on a brand new lamp, I have opened another thread seeking information from the community about this family of lamps. Specifically concerning the center terminal. The thread is titled "Need Info on Lamps using P28S Socket."
[Note from Mod.: First post of cited thread is directly above. As we already have too many disparate threads on the MPF socket and lamp base, threads merged into one.]
I hope to find a vendor with a lamp with a smooth and bright terminal.

Let's see where this takes me. Right now, I have a big problem with the contact. As I state, in all my years of experience working in electronics, this is NOT how you make a good electrical contact

 

[ship]

Another update.

After yesterdays discovery of rough contacts on a brand new lamp, I have opened another thread seeking information from the community about this family of lamps. Specifically concerning the center terminal. The thread is titled "Need Info on Lamps using P28S Socket."
[Note from Mod.: First post of cited thread is directly above. As we already have too many disparate threads on the MPF socket and lamp base, threads merged into one.]
I hope to find a vendor with a lamp with a smooth and bright terminal.

Let's see where this takes me. Right now, I have a big problem with the contact. As I state, in all my years of experience working in electronics, this is NOT how you make a good electrical contact

Switching to it.

 

[ship]

Another update.

After yesterdays discovery of rough contacts on a brand new lamp, I have opened another thread seeking information from the community about this family of lamps. Specifically concerning the center terminal. The thread is titled "Need Info on Lamps using P28S Socket."
[Note from Mod.: First post of cited thread is directly above. As we already have too many disparate threads on the MPF socket and lamp base, threads merged into one.]
I hope to find a vendor with a lamp with a smooth and bright terminal.

Let's see where this takes me. Right now, I have a big problem with the contact. As I state, in all my years of experience working in electronics, this is NOT how you make a good electrical contact

Met with Mark last week and amongst other topics we did discuss this topic. No Osram won't be making lamp sockets in the future, but yes given the interest perhaps as opposed to a ball contact, a larger nickel plated contact plate is in the furure.

Rough contacts I didn't ever note before on any brand of type of this hot center point bean of the lamp, I am sure photos would be of interest to me as a retailer and Mark as a maker of would be interested in your notes about.

First question of the rough cotact though is if on a new lamp or one - just to confirm.

 

[Ken Johnson]

ship

Thank you for contacting Mark.

I went to the college this morning to ask about their last shipment. The PO shows an August 2014 purchase. This is a new purchase and I assume this is the current product. They have three cases of Osram lamps on the shelf. I opened one of them last week. That is when I found the very rough center contact. I am sorry, but there is no way this will make a good contact with a socket.

Looking through their collection of bad lamps, I found Osram, Ushio and Eiko. The Eiko 'appears' to have a smooth contact, but I can not confirm this due to burning where the contact arced in the socket. This could be an example of a good lamp into a bad socket. The Ushio was so badly burned, I could not tell what it originally looked like. I did find something disturbing on two Osram lamps. The other terminal showed distinct signs of arcing where it connected to the shell. This appears to be a welded connection and I would not expect a problem here.

We are in a real quandary right now. There are 24 of these instruments in the house and we need them. We know we need to replace sockets, but I feel that if we put these lamps in them, with the rough contact surfaces, we will just start the cycle again and damage the new sockets. My original plan to add a brass washer to the lamps to improve the contact area is NOT long term viable even IF it works. Les has pointed this out and I agree. Polishing the contact is another possibility, but difficult to do well and provide a sufficient contact area. Then there is plan 'C', using lead free solder that melts at just over 200 C, coat the contact as evenly as I can, stick it in a socket and see what type of contact area I get. Then hope the solder does not melt and solder the lamp to the socket.

Ship, I have read several comments about sockets only lasting two to three years. The college has some instruments over thirty years old and they work just fine. The 1KW scoops are real work horses and they have been running for years. If sockets are failing after two or three years, someone needs to look into it.

I will take some pictures Wednesday and then figure out how to post them.

Ken

 

[derekleffew]

The 1KW scoops are real work horses and they have been running for years.

This brings up another point: there's lots of airspace for heat dissipation in a (14" or larger) scoop fixture. In the Altman 1KAF, especially with a 1000W lamp, lots of heat trapped inside. Perhaps consider using the 575W BTH lamp; due to its higher color temperature, it seems brighter than it actually is. Since the Altman 360 and other radial ERS use the same socket, one would think it would have a worse issue as the lamps are BBU, but that's not the case. Perhaps because the 1K EGJ was never approved, or the ERS somehow has better cooling than the 6" Fresnel. @Ken Johnson good luck, and do let us know the outcome.

No Osram won't be making lamp sockets in the future,

So much for holding ONE manufacturer responsible for the problem. Back to finger-pointing.