1926 Atwater Kent Model 20 Compact & Model L Horn Loudspeaker

This is a 5-tube battery-powered set made by Atwater Kent Radio of Philadelphia, PA. Shown with the radio is the matching horn speaker. This arrangement is the classic antique radio seen in many old movies and photographs.

The radio is housed in a narrow wooden box. The radio is a Tuned Radio Frequency (TRF) radio using a grid leak detector. Tuning of the 2 RF stages and the detector stage is accomplished using three separate knobs on the front. The knobs' dials are calibrated from 0 to 100. The smaller knob between the two larger dials is the antenna tap switch.

The knob cluster on the far right contains 2 rheostats and the On/Off switch. The rheostat on the left controls the filament current to the 2 RF amplifier tubes. The rheostat on the right controls the filament current to the detector tube and the two audio amplifier tubes. You adjust these rheostats to obtain the desired volume and clearest undistorted sound. The On/Off switch is pulled out to turn the radio on and pushed in to turn it off. Basicly, the switch disconnects ground from the filaments.

I received the radio, the speaker, and the original instruction book with this radio. Reading the book is almost as interesting as working on this radio. When received, the radio had several problems that could be fixed with a little effort. The speaker, however, worked - its driver checked out OK using an audio signal generator. The radio had the following problems:
- 2 of the 5 tubes had open filaments
- one of the tube socket tabs on the 1st RF tube had broken away from its rivet
- the primary of the 2nd audio transformer was open
- the grid resistor in the 1st RF stage was open
- the wire ends of the battery cable are frayed
- the wires of the speaker are broken and frayed

The radio chassis has a layout similar to the Atwater Kent Model 42 I have. Below is a picture of the rear of the radio chassis removed from the case.

Below is a picture of the top of the chassis. All 5 tybes are Cunningham balloon-type 01A tubes.

Below is a picture of the bottom of the chassis.

The manual is quite interesting. It contains information on how to install antennas, how to connect the batteries, and how to operate the Atwater Kent Model 30, 32, 35, and 20 Compact radios. It also discusses how to use a higher power audio tube for the second audio amplifier - essentially is requires a higher plate voltage (135V). Below is a picture of the front of the instruction book. The inside title page shows a sketch of the Atwater Kent factory. A picture of it also is shown below. It apparently was a very large factory.

The book also showed several pictures of installations of the Atwater Kent radios. Here is one such picture from the book showing the Model 20 and its horn loudspeaker.

Here is a page from the book showing the location of the tubes and controls for the Model 20.
Here is a page from the book showing the dial settings for the Model 20. Most of these stations are still on the air today.

Finally, here is a page from the book that shows how to hook up the cable to the batteries. Note that 4 batteries providing 5 voltages are required to operate this radio.

Tube Compliment

1st Audio
Audio Output
Tuning Eye
Rider's Manual Page #
2 x 01A

I performed the following actions to make this radio operative:

- replaced the defective tubes
- repaired the tube socket tab using a 2-56 screw and nut
- melted the tar out of the defective transformer can, removed the defective transformer, and inserted a replacement transformer in the can (see my AK 30 page for details on how I did this)
- used conductive epoxy to repair the open resistor in the grid of the 1st RF stage
- repaired the frayed power and speaker wires

The radio works well now using a power supply I built. With a long wire antenna, I can recieve WSM in Nashville (100 miles north) quite well.