Personally, I don't like f/stop timers at all and, IMO, they are hype. I realize that that is not the subject of this thread but I noticed that the first response did not answer your question but rather praised f/stop timers instead. I have used one but would never think of buying or using one in the future. I find standard timers to be much more intuitive and easier to use and allow for finer control. I have sometimes suspected that f/stop timers were a solution searching for a need. But hey! Each to his own.
As for the load consideration: It's nice to know that it is safe to use all timers with Zone VI cold lights but if there is any doubt, Aristo made a contactor to isolate the delicate circuitry of some digital timers. I have used one for years on one of my enlargers. It's really just a remote switch that closes a circuit to turn on the enlarger lamp while bypassing the timer. They sometimes come up on eBay but I suppose similar generic devices are available through electronics supply houses. I have an extra one and I may put it on eBay soon.
I question the post that says that you don't need one (with some timers) if you are using a Zone VI Cold Light Stabilizer. Out of curiosity, I just went down to my darkroom and reviewed the wiring of my stabilizer and timer. The Stabilizer gets it's AC current from the timer. It is not plugged into an AC outlet. The only connections it has are to the cold light, the sensor, and the timer. In other words, they are wired in series. The timer is still supplying the current to the cold light except the stabilizer is wired in series with it to regulate the current to the cold light depending on variations in the light output of the cold light that the sensor detects. I am definitely not an electronic's person but I think that means that if you have a timer that cannot handle the inductive load of a cold light, adding a stabilizer does not eliminate that problem. It would have to have it's onw AC connection to do that.
I have an Aristo 1200 contactor in the circuit that really does isolate the timer. It plugs into an AC outlet which goes to the cold light. In that setup, the timer merely closes a circuit in the contactor but it is the contactor that handles the load to the cold light using its own AC source. My timer with that enlarger is a Gralab 450 (with the light blue expose bar) and I asked the folks at Gralab at the time I bought it if it could handle the load of my (then) Aristo cold light and they advised me to use a contactor or risk burnign the timer out. I have used the contactor ever since, even after switching to a Zone VI head so I could use the stabilizer. But I believe that some later versions of the same timer did not need to be isolated from the load of the cold light.
My other enlarger uses a Zone VI compensating timer which can handle the load of a cold light with no problems, of course.
Digital timers are expensive so if you have any doubt, you may want to isolate it from cold light load. It can't hurt anything and it may save an expensive digital timer from being fried.
Last edited by ZoneIII; 08-02-2011 at 09:25 PM. Click to view previous post history.