Emerson Model 706B Plastic Radio (1952)

     

This charming set is one of the smallest five-tube radios that you'll ever see. It measures only five inches wide and six inches high!

Emerson produced two very similar models in 1952. The 706B, shown here, has a reverse-painted grill with a three-dimensional waffle design. The 707B is identical, except that it has a more dramatic "sunburst" grille, with louvers radiating up from the central tuning knob.

According to the factory parts list, this radio was offered in several color combinations. In addition to the brown cabinet shown here, it came in ivory, grey, maroon, pink, gunmetal, and yellow. The front grille piece was available in gold, gold and silver, or gold and ruby.

As you can see more clearly in the second photo, the bottom edge of the cabinet has the name EMERSON in large raised letters.

There's no room for complexity or frills in such a small chassis. As the third photo shows, the electronics are quite cramped.

The close quarters make this a difficult radio to repair. It's hard to avoid melting insulation off nearby wires with your soldering iron, or accidentally pushing two connections together to form an unintended short circuit.

Restoring the electronics was simply a matter of cleaning the controls and replacing the usual capacitors. As soon as I thought I was finished, a puzzling problem arose, however. The radio sounded great for a few minutes, but as soon as it warmed up fully, it developed a thunderous roaring sound that drowned out all signals. Carefully rechecking my work against the schematic, I confirmed that I hadn't made any wiring mistakes. Resistors can sometimes introduce noise, but replacing a couple of resistors in likely spots did not improve things, either.

It's also possible for a tube to become noisy, generating noise even though it may test "OK" on a simple tube tester like mine. This radio used two different audio output tubes, either a 50C5 or a 50B5, with slight circuit variations for each tube. Mine happened to use the 50B5, which is much less common than the 50C5. I don't own any other radios which use a 50B5, so I couldn't try out the Emerson's tube in another working radio. And I didn't have any spare 50B5s in the house, although I did have several new 50C5s in stock.

I solved the tube-replacement/testing dilemma by rewiring the audio tube socket to use a 50C5 instead of a 50B5. Unfortunately, with a brand-new 50C5 in place, the radio still exhibited the same symptom.

Having run out of clever ideas, I donned my magnifying eyepiece and began a minute inspection of the entire chassis, looking for some place where a crumb of dripped solder or a bent wire might be causing a short circuit. This paid off in just a couple of minutes. Although not easily visible to the casual eye, the magnifier revealed a place where one wire of the multi-component "R.C. coupling unit" just barely touched the frame of the tuning capacitor.

The R.C. coupling unit consists of five capacitors and three resistors all sealed in a flat ceramic case about the size of the end of your thumb. All of the leads coming out of this case were covered with braided insulation, but one lead was bent sharply where it entered the the ceramic case, exposing just enough bare wire to short against the edge of the tuning capacitor frame. I pushed the connection away from the tuning capacitor, turned the radio back on, and it worked perfectly.

I have seen similar combined resistor-capacitor units in other 1950s radios, usually small, inexpensive sets in which the lowering of parts count and labor cost would permit a lower sales price. Historically, these components form a bridge between "old" radios in which every component is hand-wired and more modern radios built with printed circuits and streamlined production methods.

With rudimentary electronics and a small speaker, this radio will not bowl anyone over with its performance. But it sure looks cute! Now that its innards have been restored, this one works as well as it ever did. Like other radios with short ferrite bar antennas, you can often improve reception by turning the radio in the right direction.

©1995-2017 Philip I. Nelson, all rights reserved