DeVere 507 dichromat bulb question

[Tjibbe veeloo]

I just bought a 507 dichromat MK 2 enlarger in pristine condition.
However I blew a lamp right away and the other stopped working at the same time,
is this normal ? I mean the other one stopping at the same time this bulb is still good . The bulbs that are in right now are the Osrams HLX 24V 250 W Xenophot.
Is this the right bulb or any other replacements ?
Thank you in advance.
Tjibbe Veeloo

 

[ic-racer]

Do you have a regulated power supply?

My experience with some regulated supplies is that if there is high resistance at the bulb contacts, the regulator ramps up the voltage which can produce arcing and subsequent bulb failure from the high current when the energy transfers across the ark. When this happens you can actually see 'burn' marks on the bulb contacts of the 'failed' bulb.

If this is your problem then the cure is to replace the bulb and socket. Sockets don't last forever.

 

[snallan]

The other lamp will not light as they are wired in series. As ic-racer says, if there is oxide build up on the socket contacts it can cause problems and lamp failures.

In my experience, I would replace both lamps, rather than just the one that has failed. The voltage/current stress that the 'good' bulb has been subjected to could cause it to fail early, which becomes a repeating pattern with each new lamp replacement. I have the 507 multigrade head, and after my first lamp failure only replaced the failed lamp. I then had three failures within a couple of weeks. However, when I bit the bullet and replaced both lamps at the same time they lasted for well over a year.

The voltage and wattage of the Osram bulb is correct, though I use the GEC ELC lamps.

 

[Tjibbe veeloo]

Thank you both Steve and IC-racer.
Steve you set my mind at ease about the lamps being wired in series.
I will keep the pointers from both of you in mind and start a search for the right
bulbs on the internet.
Thanks again,
Tjibbe