how do i know if this is right for my speedotron d1604? im new to photography let alone the eqipmet. just want to make sure i don't buy the wrong one. thanks.
Afraid I won't be much help. I have two M11 heads and 2 MW3R heads with a d1604 power unit, bought as a kit, I do know this bulb works w/the M11 heads w/the d1604. Don't know about the 103B. I do seem to remember when researching which one to buy, there were two similar bulbs in the Adorama catalog, and I made what turned out to be the right choice based on wattage and shape (compared to the one I broke).