How To Date A Neumann U87 Capsule
One capsule has dominated Neumann's mics over decades: the original K67 and its descendants.
Here is a rough overview of K67/87/870 capsule generations.
1. Similar appearance as K47/49, but with two backplates mounted against each other with four M3 screws (if I recall correctly). Brass diaphragm rings, no threads for capsule mounting screws in the backplates (this capsule version was mounted via a three pointed set screws threaded into the mounting ring), ca. 1960-1961
2. Same as above, but mounted to the capsule holder with four M2 threads (four threads in each backplate half), ca. 1961 to 1964
3. Same as above, but with brown fiberboard diaphragm rings replacing the brass rings, ca. 1964 to 1966
4. First generation of plastic diaphragm rings (ivory color), whose mounting screws were recessed into the plastic, to be flush with the ring's surface, ca. 1966 to 1980
5. Same as above, but with white instead of ivory-colored rings
6. Same as above, but diaphragm mounting ring screws no longer recessed, since 1980
Versions five and six went through five generations combined; their subtle differences through time are only noticeable to an expert. Likewise, it's initially not easy to separate a K67 from a K87 by looking at it. Upon closer inspection, you can see the 40µ aluminum separator ring between the two backplate halves on K67/870.
Since the late 1970s, all K67/87/870 are marked with a black paint/felt single digit indicating the last digit of the year of manufacture (i.e. "7" for 1987, 1997, 2007, etc.) This can be confusing because numbers repeat every 10 years. But the combination of build characteristics and date number allows pinpointing the year of manufacture.
©Klaus Heyne 2016