Altec Model 633A (1949–late 1960s)

It weighs 10 ounces and is barely 3½ inches long. It fits in the palm of your hand.

Overview

The Altec Model 633A is a compact, no-frills moving coil dynamic microphone. It spent decades in radio booths and broadcast studios, where the job called for durability and presence. Western Electric developed it as their final dynamic mic design, and it emerged in 1937. Altec Lansing took it over after the spin-off of ERPI. Production under the Altec name began in 1949 and continued into the late 1960s, with some sources citing a peak in the mid-60s. The nickname "Salt Shaker" comes from the ridged casing and perforated top. The design put function ahead of form.

The 633A found a second life in modern recording, and not for fidelity. Reviewers call it a "great 'go-to' lo-fi mic," with a bright, raspy top end that cuts through dense mixes. It is not a neutral microphone. The frequency response spans 35 Hz to 12,000 Hz, but in use there is a pronounced upper-mid bite that demands de-essing on lead vocals. That same edge makes it a good fit for background vocals, where it can sit just behind the lead without blending in. On punk-rock guitar solos or snappy acoustic textures at a distance, it gives an "odd-sounding" but effective tone. The most surprising use is inside the kick drum. There it produces a tight, beater-forward sound with low-end clarity that some describe as surprisingly modern. It can stand alone or complement an external mic when the bass needs more room.

The 633C variant has selectable impedance (30/50 or 150/250 ohms) thanks to an internal transformer. The original 633A runs at a fixed 30 ohms directly off the voice coil. Altec switched the diaphragm from aluminum (used in Western Electric versions) to Mylar, which reportedly smoothed the response slightly. The core sound is still aggressive. Mounting is standard via a ⅝"-24 thread. Placement can be vertical (omnidirectional) or horizontal (directional), though documentation on this behavior is sparse.

Specifications

Manufacturer	Altec Lansing
Product type	Moving Coil Dynamic microphone
Production years	Manufactured from 1949 to around the late 1960s
Type	Moving Coil Dynamic
Frequency Response	35 to 12,000 cycles
Polar pattern	Omnidirectional
Output Impedance	30/50 ohms
Output Level	–55 dBm/10 dynes/cm²
Dimensions	3½ inches long, 2 inches diameter
Weight	10 ounces
Finish	Instrument gray
Mounting	⅝"-24 thread
Impedance type	Single impedance mic
Internal construction	Has no transformer
Diaphragm material	Mylar

Key Features

Salt Shaker Form Factor with Perforated Dome

The nickname "Salt Shaker" is a literal description. The cylindrical body measures 3½ inches long and 2 inches in diameter. The top is capped with small holes arranged in concentric rings. This perforated dome protects the internal diaphragm while allowing omnidirectional sound entry. The ridged edges give a grip and a look that is easy to spot on studio shelves or vintage radio consoles. It is built entirely in instrument gray, with no cosmetic flourishes.

Fixed 30 Ohm Output with Direct Voice Coil Connection

The 633A has a fixed output impedance of 30 ohms, tapped directly from the voice coil with no transformer. This contributes to its ruggedness and low-noise operation in high-SPL environments. It also means the mic needs careful impedance matching with preamps, especially in modern setups where higher input impedances are standard. Leaving out the transformer simplifies the signal path but limits versatility compared to transformer-coupled designs.

Mylar Diaphragm for Smoother Response vs. Aluminum Original

When Altec took over production from Western Electric, one of the key changes was the replacement of the original aluminum diaphragm with one made of Mylar. According to available documentation, this shift was intended to produce a smoother frequency response. While the spec sheet still lists the same 35 Hz–12 kHz range, user reports suggest the Mylar version tames some of the harshness inherent in earlier builds, making it slightly more usable in contemporary recording scenarios.

Threaded Brass Ring That Resists Disassembly

Owners report that the brass ring securing the casing is threaded on with excessive force during assembly, which makes disassembly a notorious challenge. Forum accounts consistently describe attempts to open the mic as "a friggin' NIGHTMARE." The ring often requires specialized tools or risks damage to the housing. The over-torquing appears to be a manufacturing standard rather than an anomaly, which suggests Altec put long-term durability ahead of serviceability.

Historical Context

The Altec 633A traces directly to Western Electric, where it was introduced in 1937 as the company's last dynamic microphone design, following the "Eight Ball" (618A). ERPI, the audio division of Western Electric, was spun off in 1937 and eventually became Altec. Altec continued making the 633A under its own name starting in 1949. The microphone saw wide use in broadcast environments, including radio stations and the United Nations. It stayed in production for nearly two decades under Altec.

Collectibility & Value

In 2004, the Altec 633A was reportedly selling for $100-$150. The market has shifted significantly since, and more recent examples have sold for over $600 each. The diaphragm is prone to being "smashed in" or "locked up," often resulting in a loss of low-end response. That is a common failure mode and leaves the mic nearly unusable without repair. Restoration is possible, but disassembly is difficult, so most owners rely on specialists who may charge a standard rate for servicing. Working condition significantly affects value, and non-functional units are often passed over.

Market Value

┌──────────────────────────────────────────────────────────────────────────┐
│ ALTEC 633                                                       Nov 2026 │
├──────────────────────────────────────────────────────────────────────────┤
│ High      $435                                    Latest            $200 │
│ Median    $226                                    Trend           ▼ Down │
│ Low       $149                                    Volume           ~2/mo │
├──────────────────────────────────────────────────────────────────────────┤
│   $500 ┤                                                                 │
│        │                                                                 │
│        │                                               .                 │
│   $329 ┤                                                                 │
│        │                                                                 │
│        │.    .        .              .   .                        .      │
│        │                       .       .                           .    .│
│   $100 ┤                  .                                              │
│        ├─────────────────────────────────────────────────────────────────│
│    vol │█    █        █   █    █     █ █ █             █          ██    █│
│        └─────────────────────────────────────────────────────────────────│
│         2026-05                      2026-07                      2026-10│
└──────────────────────────────────────────────────────────────────────────┘