RCA 77-A
| Type | Ribbon |
| Polar pattern | Variable pattern |
| Diaphragm | Small |
| First decade of production | 1930s |
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Description
This is the RCA Type 77-A, forerunner of the 77-DX. Grand-daddy of the ribbon microphone, the 77-A is among the rarest of the RCA ribbon mics. Designed by Dr. Harry F. Olson, RCA’s lifelong resident audio genius during the late 20s and early 30s, the 77-A set the performance benchmarks for all RCA ribbons to follow for the next four decades. It is rumored that prototypes actually existed in 1929 and 1930; however, the 77-A wasn’t announced until 1932. It featured two vertical in-line ribbons and an acoustic labyrinth inside the case, which enabled it to be uni-directional. The 77-A is a huge microphone resembling a cannon shell with a large perforated windscreen on the top portion. It is gimballed at its center of gravity in a U-shaped fork.
Design, Specifications and Technical Data
Output Impedance: 30,150, and 250 ohms
Load Impedance: Open circuit
Effective Output Level at 1,000 Hertz (all output connections):
- Bi-Directional (B) –54 dbm
- Uni-Directional (U) –57 dbm
- Non-Directional (N) –60 dbm
- L-1, L-2, L-3 between –54 and –57 dbm
Output Level for Speech at Two Feet (all output connections):
- Bi-Directional (B) –61 vu
- Uni-Directional (U) –64 vu
- Non-Directional (N) –67 vu
- Hum Pick-up Level: –125 dbm
Dimensions and Weight:
- Length: 11½ inches
- Width: 3¾ inches
- Depth: 2½ inches
- Weight: 4½ pounds
- Mounting: ½-inch pipe thread