VOLUME 13 APRIL 1996 NUMBER 4
Sears Silvertone Commentator RadioBY HAROLD ISENRING
From Antique Radio Classified for April 1996
(Copyright 1996 by John V. Terrey - For personal use only.)
This article on the Sears "Commentator" radio has been a long time coming. There is a lot of misinformation about this popular midget radio, most of which concerns production dates. There were, in fact, two models, one prewar version in 1939 and a slightly modified postwar version in 1946. Outwardly, they perform and look the same. (Editor)
In early 1939, Noblitt-Sparks (Arvin) of Columbus, Indiana, a supplier of Silvertone radios for Sears, came up with an excellently designed midget radio to replace the successful "Election Model." (See my article in A.R.C., October 1992, pages 8-9.) The replacement was the "Commentator model," a 5-tube superheterodyne with a built-in loop antenna in a surround plastic cabinet. The postwar version, a Model 7004, is shown in Figure 1. It has four mechanical push buttons that push down, thus assuring cabinet position stability.
There are three cabinet colors -- walnut, Model 3351; ivory, Model 3451; and a solid onyx, Model 3551 (not Catalin). The ivory cabinet is solid black plastic sprayed with ivory-colored lacquer. It has red knobs and push buttons.The walnut and onyx models have gold knobs and push buttons. The tubes used are Types 12A8GT, 12K7GT, 12SQ7GT, 35L6GT and 35Z4GT. The radio uses a 120-volt C7 lamp, so a rectifier like 35Z5GT with a tapped heater for a 6-volt pilot lamp is not needed. The price range for these models was $9.95 to $12.95.
Figure 1. The Commentator Model 7004, a 5-tube superheterodyne with a built-in loop antenna in a surround plastic cabinet.
Source of the Name
Like the "Election Model" before it, this radio needed a name. In early 1939, war clouds were gathering in Europe. At that time, most Americans could trace their ancestry to Western Europe, and they were very concerned about what was happening in the "old country."
The only sources of news were daily newspapers and theater newsreels. A radio newscast was a rarity, until a successful 5-minute radio news report by Elmer Davis began to be aired every evening at 7:55 CST. The warring nations broadcast their propaganda to the U.S. via shortwave radio, and so shortwave radios became very popular.
The radio networks began to send reporters to Europe to get the truth about the war. These reporters, all famous names by now, began 15-minute evening reports daily. After the news, they usually brought in military and political experts for interviews. Soon these reporters began to comment on the news of the day themselves, and so they were called "commentators." Thus, Sears picked up on this great name for the new radio that could receive newscasts anywhere in the house with its built-in loop antenna. [This radio, and those of similar design were also often called "Candy Cane" radios due to the curved shape of the plastic dial.]
Early on, after the set was in the field, a problem of oscillator drift was noted. The set drifted low about 12.6 kHz during the first hour of operation. This made push-button setup a problem. It was recommended that the push-button cams be set while the set was cold and the drift annoyance compensated for by the manual tuning knob as it occurred. Radios of the competition of the era also had drift problems but with a few as low as 2 kHz. By using negative temperature-compensated capacitors, I have reduced the drift in my Model 7004 to 4.5 kHz.
There were some early failures of the C7 pilot lamp. C7 pilot lamp filaments vibrated badly if the set was played loud.
There was also a problem with the models using gold knobs and push-button caps. They were made of solid yellow plastic sprayed with a gold paint. The paint soon wore off exposing the yellow plastic. In later production, the knobs and caps were solid gold-colored plastic which looks as good as new today. As our country feverishly prepared for war, certain parts shortages occurred. Due to the shortage of Alnico for magnets, the PM speaker was replaced with an electromagnetic speaker with a 3000-ohm field. The field was connected in shunt with the B voltage.
Plastic for cabinets became unavailable due to war production. Early in 1942, before the government stopped civilian production of radios, a Model 7020 with a metal cabinet patterned after walnut Model 3351 but without push buttons was produced. [See A.R.C., January 1993, page 7.] An ivory Model 7022 was also made. The metal cabinet prevented the use of the loop antenna in its old position. The depth of the base was increased by 11/2 inches, and a Faraday shielded loop was mounted in the metal base. The antenna worked suprisingly well.
In early 1942, as production was nearing an end, Sears ordered that a quantity of parts be squirreled away so that it could be first on the market with a radio after the war was over. The set reappeared in the stores for the 1945 fall and Christmas seasons.
In early 1946, Arvin slightly modified the set to use single-ended tubes [i.e., tubes without the grid cap associated with the Type 12A8GT and 12K7GT]. The new model used 12SA7GT, 12SK7GT, 12SQ7GT, 35L6GT, and 35Z5GT tubes. The postwar production had new model numbers -- Model 7004, walnut; Model 7006, ivory; and Model 7008, onyx. The new design worked as well as the old models but with the same drift problem.
After the set was in the field a while, it began appearing in the shop with a weird problem. The sharp IF amplifier was becoming broad. Some, as viewed on a scope with a swept oscillator, were double-humped.
It turned out that the IF transformers were impregnated with a very low temperature wax. As the inside of the set heated up, the wax melted and gravity pulled the top winding closer to the bottom winding and thus modified the response curve of the IF transformer. In some cases, the top coil actually reached the lower coil producing an over-coupled, double-humped characteristic.
This overcoupling caused each station to appear on two spots on the dial. Arvin responded to this problem by increasing cabinet ventilation. The top of the rear grille cloth was folded back on itself to produce a 3/8-inch slot at the top. Arvin, of course, had the IF transformer vendor change to a wax more resistant to higher temperatures.
In spite of its few problems, the Commentator was a very popular radio. I am proud to have a walnut Model 7004 radio in my collection.
(Harold Isenring, 10850 Amy Belle Rd., Colgate, WI 53017)
Since retiring in 1981 as Electronics Service Supervisor from Sears Roebuck after 47 years with the company, Harold Isenring has continued to pursue the hobby, begun in 1935, of refurbishing antique radios. He holds an Advance Class Amateur Radio license W9BTI and an FCC General Radio Telephone Operator's license. He has written articles for "CQ," "Ham Radio," and "QST" magazines.