I finally figured out how to power the Sennheiser MKH-104, 404, and 804 from 48 V phantom power. It works like a charm. Thanks to everyone for their input and assistance. The details are here. The link also includes my subtly different version of the T-Power adapter from the others on the net (nothing wrong with them, either). The MKH-x04 mics date from the mid 1960s, and my MKH-804 still sounds very good. The MKH-416’s that I have (probably from the early 1980s) are a bit brighter, but there’s nothing wrong with the sound of the 804.

Please note that connecting any microphone other than the intended one to any of the adapters shown in the link may severely damage the microphone. In general, while the vast majority of dynamic microphones and some ribbon microphones can work with phantom powering, it is a good idea not to send power to microphones that don’t need it.