I had a Durst L1000 with a Pavelle color head. The fan was external
with a flexible duct that connected to the head. I made a little
circuit using a Triac and capacitor that:
When the lamp was on, the fan was off but the capacitor charged
through a resistor (hand picked for the job).
When the lamp turned off, the capacitor turned on the (through a
resistor also picked for the job) Triac, which turned on the fan, and
kept it on while the cap discharged.
I picked the resistor values so that the fan ran for twice the time
that the lamp was on. So, no vibration during exposure and the lamp
cooled as soon as the exposure was over.
I ran this enlarger this way for about ten years with no bulb
burnouts from heat or hot/cold cycling. Everything was happy, including me.
Now my ZBE Starlite 55 head has a built-in fan that turns on only
when the lamphouse reaches a certain temp. It usually turns on during
an exposure but even using the most powerful grain focuser, I cannot
detect any fan vibration. My largest prints are dead sharp, assuming
a sharp neg.
Jim
At 06:20 PM 1/28/2006, Peter De Smidt wrote:
I used to have a De Vere 504 with a similar setup. There was a large power supply/fan connected to the head with a flexible hose. Mine had a squirell cage blower that really moved a lot of air. Too much air, really. You might consider changing to a more flexible duct that doesn't transmit very much vibration. I considered using a flexible dryer vent, but I never got around to it. You might also consider getting a control that allows you to run the blower at a lower speed.
Don't use a light dimmer, as these are bad for the motor. Perhaps a ceiling fan speed regulator would work. Turn on the enlarger lamps and feel how hot the head gets. Now run the fan at a lower speed and check the head temperature. As long as it doesn't get too hot, you should be ok.
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