Bulb burnout on Beseler DGA head

[Kloppervok]

When i got the head, the lamp it came with was non-functional, so i ordered two more. Unfortunately tonight, one of the new EJL lamps went out. Since i had a spare, I replaced it.

To my surprise, about 30 minutes later, the second bulb also burned out. My enlarger is connected into my timer, which is correctly into the power regulator, so that's not the issue. I did about 200 sheets of b/w last week with no problems.

After examining the dead bulbs, I saw that the first one had a crack in the ceramic support, and the second bulb was engorged (see image below). There are also some cracks in the metal color backing. In both of these, the filament is mysteriously intact.

What could be happening here? I only started doing color printing today, though i don't see how that could be related.

Though it looks like heat damage, that would imply a voltage spike, which shouldn't be possible, because of the regulator.

 

[Bob-D659]

Does that head have a cooling fan and is it working? No cooling is a good way for the bulb to have a very short life. I'd replace the bulb socket as well, they have a very short service life when used with high wattage bulbs.

 

[Kloppervok]

It has a fan with a working motor. It didn't generate any problems when printing black and white.

I called Atlanta Light Bulbs, and one of their representatives told me the item i wanted was a mr16 socket.

Could you walk me through how to set up the socket in the enlarger? There also seems to be a much bigger variety of EJL bulbs than I thought. Is there a 'more' correct one to get?

 

[ricksplace]

It has a fan with a working motor. It didn't generate any problems when printing black and white.

I called Atlanta Light Bulbs, and one of their representatives told me the item i wanted was a mr16 socket.

Could you walk me through how to set up the socket in the enlarger? There also seems to be a much bigger variety of EJL bulbs than I thought. Is there a 'more' correct one to get?

I'm not at home right now, or I would check what kind of bulb is in my enlarger. I'm not sure of the method of replacing the socket. Might be a good idea to ask an electrician friend to change it for you. I bought a bunch of bulbs from www.replacementlightbulbs.com for $5 each (new old stock). They seem to work fine. They are only good for about 50 hours, which is actually quite a bit for use in an enlarger. I just changed the bulb about a month ago. Everything is fine so far.

Note that you should not touch any part of the bulb with bare fingers. Wear gloves when you handle the bulb. Skin oils cause hot spots on the bulb, and contribute to premature bulb failure.

 

[John Koehrer]

When you get the new socket, it only has two wire. There's no polarity to deal with so it's very straightforward to swap it out.
The one in the head is most likely crimped in place so you need to cut the wires & either crimp or solder the new socket in place. Put heat shrink over any exposed metal.

 

[fotch]

Nice photo.

 

[Kloppervok]

I was told to be careful and only cut in a cooler area of the head, as opposed to close to the bulb. Can I literally, just yank out the wires going into the socket, and just use a new socket, ignoring the wires?

The best thing i've heard so far is to splice it and use heat shrink wrap.

 

[ic-racer]

Are there signs of arcing (sparking) on the bulb contacts? I had a case where a bad socket caused a poor contact. The pulse-width-modulated power supply ups the voltage until it sparks across the bulb contacts and can't ramp the voltage down fast enough and the bulb blows.

 

[Dan Williams]

The MR-16 is a low voltage lamp so your system also has a transformer. It is possible that there is a problem with the transformer. Over-voltage will cause shortened lamp life. The transformer output should be 12 volts AC

Dan

 

[Kloppervok]

Is there any way to check the voltage output without killing myself with life current?

 

[fotch]

Yes, find someone who has and knows how to use a volt meter.

 

[ic-racer]

Though it looks like heat damage, that would imply a voltage spike, which shouldn't be possible, because of the regulator.

Are you sure you have a regulator? Without a picture I'm just guessing. But options would be:
1) Standard Transformer (in which case voltage spike could blow the bulb)
2) Ferroresonant Transformer (has reasonable voltage stability without additional electronics)
3) Pulse-width-modulated power supply, or 'switching' supply that electronically chops up the 120 to give a regulated x bulb voltage.

EJL is a 200W 24v bulb. If you have just a transformer, its going to be quite a heavy box to power that size bulb.

 

[ricksplace]

You can buy a small multimeter at your local hardware store for less than $20. Handy thing to have around the house too. Go ahead and test the voltage to your bulb, it should be 12 volts, so you won't get a shock even if you touch the bare live wires.

 

[bdial]

it should be 12 volts, so you won't get a shock even if you touch the bare live wires

It should be 12 volts (24 actually), but it might not be, especially considering the symptoms. Best not to touch any bare wires until you know for sure.

 

[ricksplace]

It should be 12 volts (24 actually), but it might not be, especially considering the symptoms. Best not to touch any bare wires until you know for sure.

You are right. Good advice.

 

[Karl K]

another possibility

It is possible that the first bulb burned out normally (although only 200 prints seems like a rather short lifespan) and the second bulb was defective.

A "leaky" bulb will turn milky white when it dies. The silvery swollen bulb in your photo also could be defective, but I agree with the previous posters to first check the voltage coming out of the bulb socket.

Where did you buy the EJL lamps? Were they old stock? If they were in a red and white GE box they could be over twenty five years old.

 

[craigclu]

I went through a similar experience and was advised about the problems with poor contacts and surface oxidation in the bulb socket (especially with this style power supply). Some emery cloth and a few minutes invested and it solved the issue for me. Hopefully, it is this easy for you, too!

 

[Bob-D659]

Yes, burnt, corroded, poor contacts cause a halogen bulb to run at a lower than required voltage, current and temperature. At a lower temp the "halogen cycle" doesn't kick in and the bulb envelope gets a nice plating of tungsten. This coating absorbs lots of infrared and overheats the glass causing that nice bulge around the middle. Halogen bulbs and dimmer switches are not a good mix either, causing early bulb failure with a blackened envelope. The same thing happens in autos with DRL modules that run the high beam filament at reduced power.

 

[Kloppervok]

Thanks for all the advice.

I used aligator clips and a cheap multimeter, but I couldn't detect a voltage spike, so I went ahead and spliced the old contacts, and replaced then with new contacts. There haven't been any problems since then.