Altec 670B Ribbon/Dynamic Mic (Vintage)
Altec 639 is similar to the STC / Coles 4033. Basically, it has two transducers – a ribbon and a moving-coil.
The microphone has three basic directivity patterns:
- P pressure (omni-directional)
- C cardioid
- R ribbon (bi-directional)
The impedance selecting switch is located underneath the name plate on the front of the microphone. Position 1: 30 to 50 ohms. Position 2: 150 to 250 ohms.
Model 670B that employs a slightly thicker, stiffer ribbon, which modestly improves the frequency response over the A series.