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Tuesday, July 14, 2015

Restoration of a 1947 Black Emerson Moderne

Emerson Mod 522 Ebony AM Table Radio ~ c. 1947
This is a post-war Emerson Model 522 which is a very popular collectible AM table radio. It was manufactured for the 1947 model year and featured unique styling in a heavy duty bakelite case with a clear plastic dial lens. The Model 522 was available only in an unpainted ebony bakelite case. The dial is lighted by a small bulb centered above the dial lens and the numbers and pointer were designed so that each number on the dial looks as if it is individually lit.

The mid 1940's to early 1950's incorporated a design style known as 'Moderne' and was characterized by modern but somewhat bulbous elements.  Examples of Moderne styling were very evident in the look of the 1950 and 1951 Chrysler and General Motors automobiles as well as much of the dark wood furniture of the period.  While the Moderne school of design was short-lived (primarily because it was fundamentally ugly), a few successes such as this Loewy inspired radio survived and viewed in retrospect are really quite beautiful and collectible.

The Emerson here was acquired a few months ago and in as-found original condition with the possible exception of the power cord having been replaced. In order to complete the circuit for testing, I also had to replace the burned out pilot light. It is an early model as the chassis uses the older Loctal type tubes. Later 511's and 522's incorporated the miniature tubes.
The case, front grill and tuning lens

Tubular cap upper left
A careful application of minimal electrical power to the circuitry showed that there were lots of problems.  The radio played but with a loud hum, a serious case of motor-boating and very weak reception.  The obvious villain appeared to be the filter capacitor (the big tubular thing in the upper left in the above picture). In addition there were a number of very iffy-looking other paper capacitors that no doubt are contributing to the several performance quality issues. Further evaluation would include checking both the capacitors and resistors to make sure they are within stated tolerances.

I have a schematic for this radio, so the next step was to test the tube pin resistances and pin voltages and compare them to the published specs.  In addition, I wanted to identify those pins that had anomalies in both resistance and voltage as that would be a great clue as to where in the circuit failed or failing components could be located. Below are my sheets showing the initial readings. Those highlighted in pink were out of spec.

Initial Resistance Readings

Initial Pin Voltage Readings
+ highlighted are pins with anomalies
in resistance & voltage
Cosmetically, the radio wasn't too bad.  The case was structurally sound with no cracks or damage and the original knobs, grill, dial lens and bottom plate were all there and in decent but dirty condition. The finish on the case seemed a little dull and given that it's bakelite, restoring shine could be problematic since bakelite can't be sanded and refinished like hard plastics. However, I felt there was good possibility that a good cleaning could bring good results.  The grill might have to be repainted for which I generally use a period appropriate color and paint type.

The radio was taken apart and the process of evaluating the condition of the cosmetics and the electrical components begun. The original power cord was in good shape but had been improperly spliced into the circuit so I completed the repair to correct that and now it is properly installed.

The above analysis strongly indicated that most of the old paper and wax capacitors were at best in marginal to failed condition and because of that,  there was a good chance some of the related resistors had been stressed and were performing outside of spec.  I decided to replace all the affected capacitors and those resistors that could potentially fail. Particular attention was paid to the high value resistors as they tend to vary greatly as they age.

Below is a picture of the (almost) completed work on the high value resistor has to be changed and I'm waiting for a supplies order to arrive so I can do that.

New components
The radio now plays really well with strong volume and surprisingly sensitive tuning.  The tube pin voltages are now pretty much in spec except those affected by R21, which will be replaced as soon as the supplies order arrives.

Below is the Voltage Measurement chart updated to this point.  The highlighted numbers are the correlated cap and resistor anomalous readings that should resolve after R21 is replaced.

Updated Pin Voltages

While waiting for parts, I turned to the cosmetics.  The case was thoroughly cleaned with a very gentle solution of dish washing detergent and soft bristle brush.  Bakelite is not like other plastics; you cannot "polish" a dull case as the original shine was baked on and cannot be restored if removed. There are some methods for emulating a bakelite shine, but luckily, I did not have to employ them here.  As it turned out, this case is really nice and the shine was preserved as a soft ebony glow which is what you want with unpainted bakelite. After cleaning and removing a couple of old paint spots, I waxed it with a carnuba based automobile wax. 

The front metal grill was in pretty good shape and I touched up a couple of places that were stained. The dial lens was a little hazy so I used a plastic cleaning compound to clear it up.  The yellow tint is patina and a function of the radio being 77 years old. I don't try to rub out the tint as I think it makes the radio look original and adds to the character. Further, it in no way affects the dial light's ability to individually illuminate the station numbers. 

The picture at the beginning of this article is the finished radio.

©2015 David Simons Big River Mercantile

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