Using Self-Ballasting MV bulbs in contact printer

[maxmaestro]

I've just acquired an old time-o-lite contact printer. It's a substantial metal beast, with four horizontal sockets with 60 watt incandescent bulbs, and a single red bulb in a vertical orientation. Above the bulbs is a height adjustable sheet of opaque plexiglass that acts as a diffuser, and above that the glass itself. The bulbs are wired through a rheostat that offers some adjustment of intensity.

I've read that self-ballasting mercury vapor bulbs can be used in standard sockets to provide UV light for alternative processes. Does anyone have a view as to whether I could put 4 bulbs of this type in the Time-o-Lite, and if so, what type and/or wattage I should try? Oh - I should mention that the contact printer allows a maximum print size of 8x10 (with masking blades to allow cropping).

Thanks

 

[Gerald Koch]

Mercury vapor lamps cannot be used with a rheostat as they will cut off when the voltage is reduced.

 

[maxmaestro]

Gerald - thanks for your comment. I'm not particularly well-versed in electrical theory - does that mean the bulbs wouldn't function at all, or that the rheostat would have to be left at full-intensity? I assume that when a rheostat is "full up" that it is essentially bypassed from the circuit - is that right?

 

[Donald Qualls]

Some rheostats (usually the better ones) have a bypass position; others still have turn or two of resistance wire in circuit even when all the way up. Easy to check, with an ohmmeter or by just opening the thing up and physically looking. Also easy to correct; a bypass switch and wire to connect it ought to cost about $2.75 at Radio Shack...

That done, if you can get mercury vapor lamps that aren't filtered or phosphor coated, they ought to work pretty well for contact printing with this kind of printer -- as a bonus, you can button it up tightly and not have to wear goggles while you print. The downside is the extremely slow startup time for most of the mercury lamps I've seen -- don't know specifically on the self-ballasting ones, but street and yard lighting used to be pretty heavily mercury vapor, before sodium lamps came along, and I recall that when turned off, they had to be allowed to cool for a prolonged period and then took 2-3 minutes to come up to full intensity after restarting (which itself sometimes took most of a minute).

An alternative that's likely to be cheaper, if slower, would be compact fluorescent (aka spiral) BLB lamps. They come in 13, 20, and 27 W ratings, start up in a few seconds and if broadly temperature controlled (say, kept between 70F and 100F) give pretty steady light after that first startup flicker. I've been using *one* 13W in a floodlamp reflector, about 8-10 inches from the print, and can make a VDB print in under 10 minutes with most of my negatives. No idea if platinum is faster or slower, but it should be easy to find out.