DISCLAIMER: This is a solution that I've used successfully. The instructions below are offered in good faith but please understand that you follow them at your own risk.
Manufacturers stopped making the original Philips 6604 bulb for the early Leitz V35 enlargers years ago. Since then, the only solution I'm aware of has been to replace the lamp holder with a modified one that permits the use of a Philips 13139 or similar bulb. That works fine but is a very expensive fix costing over £100 if I remember correctly for the specially machined part that replaces an original part and accepts the 13139 bulb.
I believe I may now have an alternative solution and it's left me surprised that no one else seems to have thought about it or written it up for the internet - at least, I can't find any mention of it. The halogen lamp used in the V35 consists of a halogen capsule with a longitudinal filament held in place in the reflector by some heat resistant cement or similar material.
|A tight fit.|
|Carefully does it!|
|Prongs should stick out about this far.|
I used a dremel tool that I bought in Lidl about ten years ago and which is still working despite spending most of the time lying in an old shed. Ideally, the drill bit should be diamond-tipped as you need something with a bit of bite to make much of an impression on the glass. I took about twenty minutes to gently widen the aperture, pausing from time-to-time to let the glass cool down. Wear a mask when you're doing this as you don't want to breathe in powdered glass. You have to remove enough material to enable the capsule to slide quite a way into the reflector so that the pins stick out far enough to engage with the ceramic bulb holder.
|All cemented up.|
|Battle-scarred but working!|
Hopefully, you now have a fully-functioning lamp and will be able to fire up the old V35 again. I bought my V35 a few years ago but only managed to make one or two prints before the bulb popped. I can't remember what exposure times I was getting then but the "new" bulb gives me an exposure of around 20 seconds at f4 on the 40mm Focotar for a nine-inch long print on 10x8 paper. I suspect that's a bit more than I'd get with the original bulb but it's not really a problem.
Good luck and please feel encouraged to leave a comment below letting me know how you got on!
* If you don't fancy doing this yourself, I can do it for you for an all-in price of £20 plus postage at cost. Send me an email and I'll tell you how to proceed.