The Seller of U67 #841 on ebay claims early U67's, like the one being sold, had titanium diaphragms with helium gas in the middle.
As can be seen in the photos the mic has a normal plastic (mylar ?) foil diaphrag.
You can see the holes in the backplate through it, something that is impossible with a metal (titan) foil of any usable thickness.
Anyway the construction of these capsules requires a non-metallic isolation ring at the edge of the diaphrag, which can be seen in his pictures too.
A full face metal diaphrag like on the KM53/54/56 wouldn't work.
The sputtering looks golden in his pics, titan has a matte silver colour.
A titan sputtering would have been lost by oxidation over the years anyway.
Even gold has it's problems after 40 years.
The helium filling - if it ever existed - would have disappeared through the years too.
Helium is a very thin gas, that can easily escape.
You would need to store the mic in a helium filled box to preserve it.
If some of the helium would enter the tube you can make it a nice glowing light bulb then
I suspect the whole thing is a myth.
At least the seller does not present any evidence, but the contrary.
Nevertheless the mic looks great.
Kind regards
Kai
