I guessed wrong :-(
In a message dated 4/4/2012 2:07:52 P.M. Eastern Daylight Time,
tronbros@aol.com writes:
The copy masters are 3/8th!I'm guessing that no "masters" were ever on 3/8ths inch tape.In a message dated 4/4/2012 1:17:35 P.M. Eastern Daylight Time, feline1@feline1.co.uk writes:A melltron 'master tape' (on reels, not a tape frame) is being auction in the current VEMIA auction.
http://www.spheremusic.com/Bargaindtl.asp?Item=9630
I'm intrigued as to its provenance...