I finally figured out how to power the Sennheiser MKH-104, 404, and 804 from 48 V phantom power (P48) which is very common on professional and many prosumer mixers and recorders. The MKH-X04 series requires -8V for operation. Please note that some portable recorders do not generate P48 even on their XLR connectors. This will not work with P12 or P24 inputs. It works like a charm on P48 inputs (at least from Mackie, Yamaha, and Sound Devices). Thanks to everyone for their input and assistance.
The link (below) 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. T power is very likely to destroy a ribbon and damage a dynamic microphone, so please use great care on the mic side of the adapter. The adapter for the MKH-X04 mics (top part of PDF) can also theoretically work with the MKH-110 series that requires +8 V powering.
The adapter at the top of the PDF is NOT available commercially as the MKH-X04 mics were long replaced by the MKH-XY5 and later by the MKH-XY6 mics. The -XY5 and -XY6 mics use standard T-power (T12). While I include a schematic for a converter from a P48 mixer to a T12 mic, it is far cheaper to buy them from Professional Sound or one of their distributors. B&H Photo seems to have them.
Note that the “X” in the above part numbers can be replaced with 1 for omni, 4 for cardioid, and 8 for long shotgun. Y is always 0 on these. On the later mics, the same pattern is followed except the short shotgun was added as an MKH-416. The part numbers are ambiguous to powering. Early ones show no powering suffix and are T12. Mid production shows either nothing or a “T” for T12 or “P48”. I believe the latest production runs have no suffix and are P48.
In NO CASE will I build you one of either, so please do not ask. Thanks for understanding (too much liability and time).