I always had the idea that the "preheater" was more of fancy name for a voltage regulator, than an actual heat source. This sounds as if it works like a thyristor in a flash light.
My question regarding the Z6 coldlight was basically because the cold light and the timer were bought at the same time, and I´d like to be prepared for the moment it stops working and know what my alternatives are (I´ve had them for 12 years). Living in a third world country where I have to mail-order everything (except for a few films and chemicals) I like to have the necessary information that allows me to solve emergencies within a reasonable time. (I have 200 new negatives and no enlarger - that´s an emergency; the timer should arrive on friday thanks to your suggestion - that´s a reasonable time)
I've never used a Z6, but the 'thermo' on an Aristo is a heater, plain and simple. It is a bank of resistors and a thermostat that heats the chamber that the tube is in to 105F.
"The Early Zone VI enlarger was a piece of junk. Picker rushed it to market with an unstable negative carrier and other problems. The light source was, however, very effective in drawing out the full responsiveness of VC paper. Its only problem (this light source - I can't speak to others) was excruciatingly long exposure times with 4X5 negs."
I have one of these enlargers and get good performance from it. I use it for 4x5 and smaller negatives. It has the following idiosynchriasies:
> Contrary to early claims, it doesn't support 5x7. It was designed as an oversized 4X5 enlarger. It's vague as to why Fred Picker gave it the 5x7 label.
> The lens boards are a bit small for 8x10 enlarging, as is the rectangular opening in the negative stage. It will work for 8x10 with a 240mm Componon that I have. (Also with a Rodenstock 270 Apo Geronar.) It has no problem working with a 150mm Componon-S, but of course, not for 8x10.
> Using the VC head for this enlarger with a compensating developing timer, one must expose the two colors consecutively versus simultaneously to obtain consistent results. (First green, then blue, or vice versa. There's only one sensor, versus a sensor dedicated to each color.)
As to being slow with 4x5 film, the opposite is the case. I use mine at low "B" and "C" settings and successfully print in just a few seconds. (10 or so.) I have no problem printing 35mm negatives with it. The head's quite a bit brighter than the later Type II heads, because the power sources for each color were located in the heavy, huge control panel that goes along with Type I VC head.
With the purchase of three, small, inexpensive screws at a hardware store, the Type I works with a Type II 8x10 head. The chassis has no problem supporting this head.
By using the Beseler adaptor, I was able to adapt a D2V condensor head to this enlarger. This should also be true for the Type II. It was trivial and only involved gluing a 1/2" strip of rubber around the metal cylinder that holds the condensors. So, I can easily switch back and forth. These Beseler adaptors are no longer made and are hard to find for the Type I like mine, but they're available for the Type II.
Contrary to being "a piece of junk", I find the Type I enlarger to be quite useful and relatively well-built. It's as well built as either an Omega or Beseler enlarger. (Not up to Durst standards, though.)
To the point of this thread, using the Beseler adaptor, either the Type I or II can be used for either condensor or diffusion enlarging.