Variable Vivitar 283
David is in the process of setting up a light kit using ever reliable vivitar 283 flashes. I think I've mentioned before that a 285 was my main strobe for several years. I've always used these flashes with their Auto setting where the flash figures out how much light it thinks the scene needs the provides that amount and cuts itself off.
With David's talk of setting up the kit, I got to wondering if there was a way to control the light output so that you could have a consistent, controllable light burst. The goal being, for example, to setup two 283s pointed at umbrellas and dial one back a stop less than the other.
A quick google and I found this page on high speed flash photography. While the topic is a little different, the solution looks like it'll work like a champ. The salient point on that page is number 5.
On a Vivitar 283, remove the Auto-thyristor module and plug a 100 k ohm variable resistor in the right two holes (as you are facing the strobe). You should then be able to dial in the amount of light you want the strobe to release with each flash. (I haven't tried this yet, but will soon. If you beat me to it, let me know if anything explodes.)
If this works, as I expect it will, I'm gonna end up buying a bunch of 283s. This will also make it easy for me to set them up someday when I start doing my infrared band photography.