Timer/Stabilizer for Cold Light Head?????

I have had for a while (10 years) an Aristo D2 series 70 watt cold light head that has never been used. I had to pack up and move before I got the old Omega D2 rebuilt enough to use it.

I am confused about what I might need to use this instrument and I'm not finding a definitive answer on the Aristo web site.

Do I need a voltage stabilizer to use this unit?

Will any timer work with this head or does it require a special unit?

Thanks in advance for any info you folks might have.

I have used the Stop Clock Vario from our sponsor R H Designs
http://www.rhdesigns.co.uk/darkroom/html/stopclock_vario.html
for 3-4 years and like it very much. I use it in conjunction with a 12 x 12” Aristo cold light head for 8x10 negatives on a converted Durst 138S enlarger. There are front and ¼ view pictures of the enlarger in my gallery.

John Powers

You don't state the vintage or model of the head, so I am supposing it is an older unit.

There should be two lamp cords coming from the head: one is for the heater and one is for the lamp. You plug the heater in about 1/2 hour before you start printing to get the lamp up to temperature. The cord for the lamp goes to the timer.

You can use any timer you want.

A voltage stabilizer is not needed.

Cold light heads have some trouble with repeatability because the light output increases after the lamp is turned on and heats up. The heater used by Aristo doesn't really keep the lamp at operating temperature, and it doesn't turn off when the lamp turns on so the lamp temperature is always rising over the course of an exposure.

If your printing cycles are repeatable - you expose for about the same time, with about the same time between prints - there shouldn't be much problem with lamp variability. Some people keep the lamp on all the time and use the red filter to time exposures. Many cold light enlargers control the exposure with an electric shutter that plugs into a timer and again leave the lamp on at all times.

There are some specialized 'compensating timers' that monitor the lamp and change the count rate as the lamp warms up. The use of a compensating timer complicates the use of an enlarging meter - both the meter and the timer will try to adjust for lamp warm up and the result is a mess unless the lamp is fully warmed up and stable when you take measurements.

Depending on the lamp installed in the head you may need to use a CC40Y (?) filter when printing with variable contrast paper. Without the filter the prints will come out at very high contrast.

I've just started working with a Aristo D2 on a Beseler 45. The instructions on Aristo's site last I read them says leave the thing plugged in (make sure to use both plugs) for at least 30 minutes or run the lamp on for 5 minutes or so. I haven't noticed problems with repeatability and I'm using a standard darkroom timer. The old owner had a CC40Y filter installed but I tried it and haven't found it really necessary. Contrast seems to change just fine using the regular Ilford VC filters. Haven't tried any extreme grades yet though. (4+, 0 etc..)

I have used Aristo cold lights for many (40+) years; my recollection is that there is a thermostat built in , so temperature is maintained pretty much at the set level. Beginning some years ago with Fred Picker and his Zone VI business, a compensating timer, designed to vary the time of exposure as the lamp varied in brightness came on the market. Still available from various sources.

I have run many tests, exposing paper to about zone VIII about 2 minutes apart to replicate making a print. I have never been able to detect a difference between exposures. Maybe I've been lucky with my electricity supply or maybe my eyesight is just not good enough, but decided long ago a compensating timer was for me a waste of money. Try using the light after letting it warm up for 15 to 30 minutes and see what happens. The worst is you might waste a sheet of paper!

I thought the things had thermostats, but the two I have seen opened up - an Omega 'D' and an 8x10 - only had heaters.