Stromberg-Carlson Model 440M Console Radio (1939)

           

My Stromberg-Carlson 440M console radio has a classic, stately look. Built in 1939, it has 10 tubes, motorized tuning, and the famous "Acoustical Labyrinth" speaker system.

This radio not only performs well, but also shows outstanding build quality and is easy to service. These are hallmarks of Stromberg-Carlson, which began in 1894 as a telephone company and quickly established a reputation for fine engineering and durability.

Description

I bought this set at a second-hand shop for $165. It was in good original condition. Notice the ornate details and front panels of matched walnut veneer.

     

The next photos give a closer view of the dial and controls, as well as the front veneer.

  

A magic tuning eye is seen in the middle of the dial, which covers three bands: standard broadcast from 550-1650 kilohertz, and shortwave from 2.5-22.5 megahertz.

From left to right, the knobs are labeled Volume, Bass (with Decrease, middle, and Increase settings), Tone, Range (to select one of the three bands), and Stations (the tuner).

Below the dial are ten pushbuttons, labeled Off, Phono, KVI, KIRO, KXA, KJR, KOMO, KRSC, KOL, KMO, Remote, and Manual. The eight call numbers are for Seattle area stations of the time. (Some, such as KOMO, are still on the air.) You can reset the buttons to any stations that you like, of course.

The Remote button selects the wired remote control if one is present. The station buttons both turn on the set and make the motorized tuner select the desired station.

The shortwave bands potentially include hundreds of stations, so for shortwave listening you press the Manual button and turn the tuner knob.

The rear view shows the chassis and the "Acoustical Labyrinth" speaker enclosure:

Below is a closer view of the chassis. A label shows the layout of all ten tubes. A small panel has terminals to connect a longwire antenna and ground.

The large round jack at the chassis's lower left is for a wired remote control. This remote was optional and I have never seen one in the flesh. If you have a photo of one, send me an email.

The beefy power transformer at the chassis's right is appropriate for a high-tubecount set like this, and emblematic of Stromberg-Carlson designs, which tend to err on the side of durability.

The round mechanism at upper left of the chassis is the motorized tuner, controlled via the preset pushbuttons. This photo shows the motorized tuner in closeup.

The dial's eight preset tuning buttons correspond to the eight adjustable leads seen in the curved slots of the tuner mechanism. The Rider's 440M service manual has instructions for setting the tuner to desired stations, as well as a schematic diagram and other service information.

It's fun to see the motorized tuner work once in a while, but for everyday listening, I use the manual tuner knob to avoid wear and tear on this 70+ year old gizmo.

Here is a list of the 440M's ten tubes and their functions.

Tube Type Function
V1 6A8 Modulator
V2 6J5 Oscillator
V3 6K7 IF Amplifier
V4 6H6 Demodulator/AVC
V5 6SQ7 Audio Amplifier
V6 6SQ7 Audio Inverter
V7 6V6 Audio Output
V8 6V6 Audio Output
V9 6AF6G Magic Eye
V10 80 Power Rectifier

The 6AF6G magic eye is my favorite tuning indicator tube. Most magic eyes are a circle with a single pie shape that opens or closes according to a station's signal strength. The 6AF6G has two opposing segments, which can be wired so that they respond differently to various signals, resulting in an eye with a sort of coarse-fine function. You can read more about such indicators in my magic eye article.

The Stromberg-Carlson Acoustical Labyrinth

The bottom third of the cabinet is occupied by the Acoustical Labyrinth, a baffled enclosure that improves the audio quality. The rear of the speaker frame protrudes from the top of the enclosure, and the label in back gives a simplified view of how it works.

Stromberg-Carlson patented this system in 1939. Here are two of the patent drawings.

  

If you're interested in audio technology, you may find the complete patent description interesting: US Patent 2,014,777.

The following brief article explains the labyrinth more in layman's terms. In a nutshell, it's designed to prevent cavity resonance and standing high-frequency standing waves, and improve bass response.

I'm no audiophile, but the 440M certainly sounds good to me. It has nice fidelity and enough volume to shake the rafters. The dual tone controls give you a lot of flexibility to adjust the tone for different sorts of music, as well.

Electronic Restoration

Restoring the electronics was straightforward. Nothing was required beyond routine capacitor replacement and cleaning and lubricating the tuner and controls.

A welcome feature is the sturdy "roll cage" built onto the top of the chassis. This lets you turn the chassis on its side or even upside down on the workbench, without damaging delicate components. If only every radio had a service frame like that!

Cosmetics

The cabinet has various scuffs and scrapes, typical of any 72-year old piece of furniture. Stripping it would be overkill. If I do anything at all, I'll lightly touch up the boo-boos, preserving as much original character as possible.

Final Thoughts

This radio sounds great and its restrained yet interesting styling is exactly to my taste. It has sat in the front entry area of our home for over 10 years.

©1995-2014 Philip I. Nelson, all rights reserved