Western Electric 639A (1938)

That deep, chesty growl on old radio dramas and live recordings? There's a good chance it came from this hulking, caged mic.

Overview

The Western Electric 639A "Bird-cage" microphone came out in 1938. It put a dynamic moving-coil capsule and a ribbon velocity transducer in one big shell, which gave engineers a lot of flexibility when most mics did one thing one way. It was Western Electric's answer to RCA's DX77 and BX44 series, and it offered multiple patterns without stepping on RCA's patents. It worked. It became a staple in broadcast studios, government chambers, and international assemblies like the United Nations.

The architecture is the interesting part. Modern multi-pattern mics use back-to-back diaphragms or complex acoustic labyrinths. The 639A used two completely different transduction methods: a dynamic element (omnidirectional by nature) and a ribbon element (inherently bidirectional). A selector switch at the base combines them to give cardioid, bidirectional, and omnidirectional patterns - three in total. The switch is labeled C (Combined), D (Dynamic only), and R (Ribbon only). That was a lot of versatility for 1938.

It stands five-and-a-half inches high and about six inches around, with a prominent wire cage that gives it the nickname "Bird-cage." Under the cage, owners report the original silk lining often remains intact. It's heavy - "a weight to match the size," as one source put it. Units were still in active use in the Denver area as late as the 1980s, and Dave Felice tracked with one through a WE 23A console from 1969 to 1971.

This mic is passive, but it's fragile in ways that matter. The dynamic capsule, about 34mm in diameter with a depth of roughly 20mm, uses thin wires that are notorious for breaking or losing connection over time. The internal components - a transformer, inductor, 620-ohm resistor, and 0.12 microfarad capacitor - are sealed in goop after assembly, so repairs are delicate. One wrong move and you're out a few hundred bucks, plus a piece of broadcast history.

Specifications

Manufacturer	Western Electric
Model	639A
Introduction Year	1938
Microphone Type	Ribbon/Dynamic (combination)
Frequency Response	40 Hz to 10 KHz
Output Impedance	30 to 50 Ohms
Height	five-and-a-half inches high
Width	about six inches around
Weight	a weight to match the size
Dynamic Capsule Dimensions	about 34mm diameter with an allowed depth of about 20mm
Pickup Patterns	Three pickup patterns — non-directional, bi-directional and cardioid
Pattern Selector	C (Combined/Cardioid), D (Dynamic only), R (Ribbon only)
Internal Components	transformer, inductor, resistor (620 ohm), capacitor (0.12 microF)
Ribbon Type	piston style ribbon

Key Features

Dual-Element Design: Two Mics in One

The 639A switches transducers, not just polar patterns. Set it to "D" and you get the dynamic moving-coil element, which is inherently omnidirectional and delivers a tighter, more focused upper midrange with noticeably less low end. Set it to "R" and you get the ribbon: full, warm, with a ton of low-end presence and good sensitivity, as owners describe it. At "C," both elements combine into a cardioid pattern. This is acoustic summation, not electronic trickery. The dynamic's omni response and the ribbon's figure-eight are blended via the internal circuit to give a directional pickup that rejects sound from the rear. That suited live broadcasts and studio isolation long before close-miking became standard.

Internal Circuitry: Passive but Purposeful

Inside the shell is a transformer for impedance matching and amplification of the ribbon's low output, an inductor, a 620-ohm resistor, and a 0.12 microfarad capacitor. These shape the interaction between the two elements and keep the combined output stable across patterns. The transformer is the critical part. It boosts the ribbon signal to usable levels while maintaining the 30 to 50 ohm output impedance, which made it compatible with the tube consoles of its era. Four wires from the transformer come up through the sealed base of the dynamic chamber, get soldered, and are locked in place with goop. That kept moisture out, and it makes servicing a real adventure.

Build and Usability

The 639A was built for broadcast desks, not studio stands. The base-mounted pattern selector switch is large and tactile, so engineers could change patterns without looking during live radio plays or political hearings. The wire cage acts as a windscreen and protects the delicate internal elements from plosives and physical damage. Under the cage, the silk lining - still found in many surviving units - helps dampen internal reflections and adds a subtle high-frequency roll-off that contributes to its "classic" tone. It lacks the sleekness of later Altec designs.

Historical Context

Western Electric introduced the 639A in 1938 with a clear mission: break RCA's grip on the high-end broadcast microphone market. The RCA DX77 and BX44 series were dominant, but their designs were protected by patents. Western Electric, working through Bell Labs, engineered a workaround that used a hybrid dynamic/ribbon approach rather than RCA's single-element capsule designs. The result was patentable: William Harry and Robert Marshall of Bell Labs secured a design patent for the 639 in early 1941. The mic competed well. It was adopted widely, from congressional hearings to United Nations assemblies, and remained in service for decades.

In October 1949, as part of a federal anti-monopoly order, Western Electric spun off its audio division to form Altec. The 639 design lived on as the Altec 639, identical in every way to the Western Electric version. The 639B followed and expanded the choice of patterns, but the 639A remained the original.

Collectibility & Value

The Western Electric 639A is still in high demand, with serviced units sometimes selling for thousands of dollars. It's frequently described as "rare vintage" and "classic sounding." Owning one takes commitment. The thin wires in the dynamic capsule are a known failure point, often breaking or losing connection with age or vibration. The pattern selector switch can suffer from contact oxidation and may need cleaning or tensioning to work reliably. A new ribbon installation is common during servicing, and it's not a DIY job for the uninitiated.

One warning stands above all: do not apply phantom power. The 639A is entirely passive and contains no active electronics, but the delicate ribbon and transformer are not designed to handle 48 volts. Doing so could destroy the microphone instantly. Even the parts donors are valuable: the Altec 633 "Saltshaker" mic, sometimes used for repairs, was selling for $400+ as of May 2021.

Market Value

┌──────────────────────────────────────────────────────────────────────────┐
│ WESTERN ELECTRIC 639A                                           Nov 2026 │
├──────────────────────────────────────────────────────────────────────────┤
│ High      $687                                    Latest            $218 │
│ Median    $313                                    Trend                — │
│ Low       $100                                    Volume           ~1/mo │
├──────────────────────────────────────────────────────────────────────────┤
│   $700 ┤                                                                 │
│        │    .                                                            │
│        │                                                                 │
│   $443 ┤                                                                 │
│        │                                                       .         │
│        │                                                                 │
│        │                                                                .│
│   $100 ┤.                                                                │
│        ├─────────────────────────────────────────────────────────────────│
│    vol │█   █                                                  █        █│
│        └─────────────────────────────────────────────────────────────────│
│         2026-03                      2026-04                      2026-05│
└──────────────────────────────────────────────────────────────────────────┘

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