I can't help you directly, but if you don't find an answer here you could try Sound on Sound forum [hope it's legal to mention other forums here].

There's a fellow used to post there frequently by the name of John Willett who is a Sennheiser rep and has just about all spec and history at his fingertips. He might still drop by occasionally. A very knowledgable guy.

I found the post on SOS regarding older MKH mics. Ends up it was a question asked to John Willet by Gunnar Ghellquist regarding a pair of MKH 406's aqcuired by Gunnar [frequently part of this forum].

The post is
http://www.soundonsound.com/forum/showflat.php?Cat=&Board=MRT&Number=9911&Searchpage=2&Main=9911&Words=MKH+104&topic=&Search=true#Post9911

Bap
Thanks! It really is very kind of you to look this up for me! 8-)

I've been on the lookout for a set from the newer MKH series, but I think I could find a use for these too.

Thanks again!
John

Hi,
just chiming in very quickly (on the run).

I found a pair of MKH406-s on the net. They are with me at every gig, and I really like them. I believe they were designed with an 80Hz high-pass filter, which generally is a good thing, but not always. Otherwise they sound very much like later MKH-s -- boring is one word I have sometimes thought. In a good sense that is, not adding anything, just catching what it sounds like. For on location recording that is perfect if you ask me.

Gunnar

Thanks Gunnar
That's great to know!
John

Gunnar,
I see you're based in Stockholm -one of the most wonderful cities in the world! I've been to Sweden three times, and two of those visits were to Stockholm.
John