Hello all !
actually it works with a smaller bulb (otherwise the Durst 138 and 139 won't sell at all ;-) ) but light is much less even on the baseboard and centering the bulb is more difficult.
These enlarger are a compromise : the bulb is staying up on a box with a square opening on it. this square opening direct the light on a 45° mirror (sitting in the front of the enlarger which explains the shape of the front face) which in turn light the double condenser system above the negative carrier. They are not straight condenser system nor diffusion enlargers but a mix between them.
In he past I used Philips Halogena 150W double envelope 220 V halogen bulbs with a large (95 mm ) bulb. But the short working time turned them with black spot soon. (the halogen system hasn't got enough time to run correctly) add to that that 150 W is not enough to get decent printing time with warm and slow papers like the Foma or the late Forte one makes me dream of a 300 W 100 mm diameter enlarger bulb !
Agx, Yes, I've seen your PM, but I searched all bulb specialist for suitable bulbs and found nothing (even NOS Philips bulbs of correct size are long gone)...
I've been told to add a stainless steel bowl at the read of the lamp to make it appear much larger, so, with the glass bulb idea I've something to play with ;-)
Thanks both for your help and advice !