The Altec 670A
multi-directional ribbon microphone
These basic patterns may be modified by placing the selector on the back surface of the microphone in intermediate positions. Such placement will result in a compromise between the adjoining patterns.
Quoted from the Altec Lansing Corporation Operating Instructions, Part No. 12182
November, 2006 update: I have managed to track down a 670A and a 670B, and record them simultaneously, although under rather adverse conditions. Apologies for the ambience. It was this or nothing. References to channels 1 and 2 represent left and right channels of this stereo recording. The 670A is on the left, while the 670B is on the right.
According to Mr. Bill Hayes at MicroMike Laboratories in Anaheim, California, there is a Model 670B that employs a slightly thicker, stiffer ribbon, which modestly improves the frequency response over the A series. Our thanks to Mr. Al Pushkin for contacting Mr. Hayes and tracking down this information.
Download the Operating Instructions for the 670.