We have had a U87ai with a tube mod by Innertube Audio (Atomic Squeezebox makers) for more than a year and I have A/B'd it with a stock 87, Old Telefunken 47, Old Nuvistor 47, Gefell, etc....and in all cases it was as good as the next best- most cases it was better....and was chosen by the singer. New they are ~$3500- which is a lot less than a used 47 or most other new comparable mics-
They also shine on acoustic instruments and pretty much anything else we have tried them on. Truly astonishingly good. The mod was only ~$1500.00 for our U87ai. Here's the link if anyone is interested:
InnerTube Audio Tube Retrofit for the U87
Here is for the Mag Light mic- same guts- different body-
The InnerTube Audio MM2000 MagMic
No, I don't work for Innertube- just a really happy customer- and Stayne is a great guy to do business with too. I think the main reason they aren't better known is they don't advertise much and it is mainly seemingly word of mouth.