Quote Originally Posted by magnarc View Post
The 'Model 604 Duplex' as opposed to the 'Super Duplex' AFAIK indicates an later manufacturing date for the 604E. Altec called the 604E 'Super Duplex on the 1968 cut sheet (when it was a division of Ling and with a NY office), but by 1973 simply the Model 604E Duplex(Altec Corporation only and only CA).
Somewhere on them should be a number 391xxx, with the x being the year and the xx the month. 391025 will be the 25th week of 1970. It may be under the diaphragm cap.
Thanks for the reply. Interesting to know they dropped the "Super". I can't seem to find a single picture of another 604e without the Super, must have been a little less common. Just biamped them, sound pretty good.