The "top of the line" Stromberg-Carlson radio just before the U.S. entered World War II was the Model 955PF. This was an AM/FM/Short Wave radio-phonograph console which was more or less "state of the art" in the early 1940's. It featured bass and treble controls, a Webster model 41 three-post record changer, and an acoustical labyrinth speaker housing, all in a beautiful wooden cabinet.

Schematic of the main chassis of the Stromberg-Carlson 955PF

Donald Dupree found this neglected model at an auction and was able to purchase it at a reasonable price. The "neglect" seems apparent by the rusty condition of the chassis and general dirtiness of everything else, as is evident in the accompanying photos.

Examining the schematic of this set reveals some interesting items. The main chassis is complete in itself, having push-pull 6L6G's in the output stage. However there is an additional chassis and power supply which also uses two 6L6G's.

This auxiliary amplifier is totally self-contained, with its own high-voltage and grid bias supplies for the two output tubes. This "power amplifier" plugs into the speaker socket on the main chassis (where one would usually connect the speaker) and feeds the output of the main-chassis 6L6's into the input of the auxiliary amplifier. Talk about over-kill!

All of this feeds two speakers contained in the acoustical labyrinth, which is a separate assembly (not a part of the cabinet structure. One of these speakers is a "woofer" and the other is a "tweeter." A choke and capacitor network in the speaker enclosure, separates the audio signal to feed these speakers.

The treble control is nothing more than the usual "tone control" found on many sets of the time. A capacitor in series with a control which just cuts the high notes. The bass control features a tuned circuit using a choke and capacitor shunted by the variable resistor control which shorts it out for less bass, and increases in resistance for more bass. The choke used here is mounted elsewhere in the cabinet to prevent induced hum from the power transformer.

The FM band, of course, is the old one of about 40 mHz. Conversion to the current 88-108 band would take some doing and it is doubtful that Don will attempt it.

The 955PF chassis. Time has taken its toll on the general appearance but not in its operation.

After minor repairs, the set worked just fine on AM. The band-switch has a broken gear which prevents checking out the short wave and FM bands, but since these are of little interest anyway, Don is content. He did note that the record changer needed some help. These old Webster changers were quite good by the standards of the day but were sometimes impossible to repair. They were made with a cast base which had a tendency to warp over the years, making adjustment impossible. To date no one has come up with an anti-warp spray can.

The power amplifier of the 955PF