I have a Durst C35.
The lamp that came with the enlarger was a Reflector Spot Lamp R63 55W with an E26 screw .
When this failed I replaced it with a R63 60W ES Reflector Spot Lamp which worked well.
The replacement lamps came in packs of two from poundland.
Next time it needs replacing I may try a50W ES R64 PAR20 Halogen Reflector Spot Lamp: http://www.consumablestore.co.uk/50w...mp-p-3863.html