Ilford 500 Bulb Blowing Blues

[AgX]

Fingerprints will not make a bulb burn through prematurely.

 

[Leigh B]

Fingerprints will not make a bulb burn through prematurely.

Fingerprints can cause cracks to form in the glass, allowing air to enter.

- Leigh

 

[AgX]

Microcracks... Maybe... did not think of that. But I rather assume the involved tensions will make the bulb disintegrate instead.

But if there were fingerprint causing harm there should be charring marks on the bulb.

 

[Vaughn]

Just thought I'd throw this out there. We had a line of 8 Beseler 23CIIs along one wall (8 Omega D5-XLs on the opposite wall).

We started to blow bulbs at an a alarming rate (considering the cost!) on the Beselers. Brand-new bulbs lasting only a couple days. And not on any one enlargers, but seemingly random enlargers. I got the Plant Operation engineers up to check on the curcuit, they even put a monitor on the line for a while and found nothing. I eventually (better late then never, I suppose) hooked my volt meter to the output of each timer (mostly Time-O-Lites). I found one that shot high voltage into the electrical curcuit when it shut off. If someone else in the line of enlargers happened to be focusing or making an exposure when the bad timer shut off, the surge in voltage would blow the bulb.

Tested them regularly after that and found a couple more over the years -- I sent them back to the factory for repair...tough little timers and well worth fixing for a high-use darkroom!

 

[Leigh B]

Charring ? ? ?

The problem is uneven temperature distribution across the surface, causing localized tension/compression of the glass.

- Leigh

 

[AgX]

Residues from fingerprints and such will char, thus causing locally excessive heating up. That is the explanation I got from industry sources.
BUT in general explanations on this issue are so scarce that one wonders.

One day I shall make a test and see what happens...

 

[AgX]

Anyway, if there is no mark of any kind at those respective bulbs, we still are not further in explaining this Ilford 500 case (aside of some mysterious mis-setting of the command unit).

 

[Leigh B]

The operating manual does mention one potential problem that's installation-dependent.

IF you use an external voltage stabilizer on the AC mains, the internal stabilizer MUST be turned OFF.

The internal stabilizer is in the control unit, enabled/disabled by a little switch on the back panel.
The switch must be moved to the 0 position using a small screwdriver or similar.

If both regulators are active simultaneously, they can cause wild voltage swings.

- Leigh