The Modern Radio Laboratories
No. 2-A Crystal Set

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A "No. 2-A Crystal Set" built from plans published by Modern Radio Laboratories.

 
MRL catalog entry from October, 1973.
The circuit was developed in 1933 by Elmer Osterhoudt. Thousands of kits were sold until his death in 1986.

 
 
 
MRL crystal radio
 
MRL crystal radio
 
This set was built in October of 2020.
 
 
The parts and layout were adhered to as closely as practical.
All parts are mounted to the front panel except the antenna and ground connections.

 
 
 
Instructions for building this set are found in MRL HB-2 and DP-22A (click for the links).
 
 
 
THE COIL
 
 
 
 
The coil form is from an actual MRL No. 2 coil made in 1984 by Elmer Osterhoudt. It was mounted in an MRL No. 2 crystal set. Over the decades it had been baked and frozen repeatedly in a garage and the celluloid shrank slightly, causing the winding to come loose. Since the No. 2 wasn't a kit from MRL, or even built to the MRL layout, I had no qualms about removing the coil. Besides, a 2-A is basically a No. 2 set, though Elmer stated that he had not been able to pick up shortwave on the 2-A.
 
The coil of wire was removed and the form was polished until it looked new. I couldn't help but think that the last person who touched the form under the wire was Elmer himself. I didn't find any fingerprints on it, or it would be in a display case right now.
 
A new coil was wound using the instructions in HB-2. A close inspection and comparison with one of Elmer's actual coils reveals it is missing a piece of black tape on the left side. Except for this, it is indistinguishable from an MRL coil made by Elmer.

 
The coil form is 2" in diameter by 4.5" long. The coil is 90 turns of #22 cotton covered wire. Taps are at turns 5, 10, 16, 23, 40, 50, 61 and 73.

Thousand of these coils for the No. 2 and 2-A were sold by MRL. What was the formula Elmer used for the taps when he made the first ones in 1933? After analyzing the coil I found he used a ruler! The coil is tapped at 1/4, 1/2, 5/8, 3/4, 1
, 1, 2, and 2 inches.
 
 
 
THE SWITCH
 
 
 
 
 
I caused myself a lot of grief by putting the switch points too close together, If solder lugs are used, they touch each other and short out the coil. The "fix" was to solder a small loop on the end of each wire.

 
I caused myself more grief when it was time to mount the variable capacitor. I followed Elmer's instruction for making a template. Then the panel was marked and the holes were drilled. When it was time to mount the capacitor I found I had put the template on the wrong side of the panel! The holes were a mirror of where they were supposed to be. Jackass!!

Well, between the switch points being too close together and the holes drilled in the wrong place, I was about to chuck the panel into the trash. Unfortunately, it was the only panel I had. 
 
No.2-A crystal set
No problem; MRL made two different size dial scales! I used a larger one, which was serendipitously found entirely by accident in a box of odds and ends. It was scanned and "cleaned up," then a brand new scale was printed.
 
The brass screw holds the coil. It is the only mounting point. Elmer's instructions say to use lock washers to keep the coil from moving. He wasn't kidding, they are absolutely required.
 

 
 
 
 
The schematic and pictorial. The "BS" switch cuts out political ads. (Actually, the "BS" switch is for "Broad" and "Selective" tuning.)

 
In DP-22A Elmer said to mount Fahnestock clips on the back of the crystal detector stand so you can use a diode. I didn't want to do this, because it meant cutting the screws. When you're using these old parts you don't want to damage anything, even a screw. I outsmarted myself and used different screws! The Fahnestock clips are 1/2 inch. The diode is a 1N34A.
 
 
 
A CABINET
 
 
 
 
The instructions say to make a wooden box for the radio, sand it, coat it with white paint and then give it a coat of Nu-Enamel.

This box is made from 1/8" plywood from a craft store. To cut it, you just score it (deeply) on each side and snap it.

Elmer wouldn't have said to use Nu-Enamel if he didn't use it himself. It wasn't an advertisement; he sometimes used brand names in his literature, and they are clues into his personal life. For instance, he said to scrub the front panel of the MRL 1-Tube DX radio with Ajax. That tells us the Osterhoudt's used Ajax Cleanser.

 
     
Using the computer to decide the color. I didn't use any of these colors.
 
It looked so good painted white decided to leave it white. It can always be changed later.
 
I came up with several methods to hold the radio in the cabinet. Obviously with the radio in a cabinet you can't access the diode behind the back panel. One idea was to use tiny Neodymium magnets epoxied into the base, which would stick to small "L" brackets in the cabinet. In the end, I just removed the diode and used tiny screws.
 
 
 
LABELS
 
 
 
  Large label Small label Click image to download.  
Labels - The labels are printed on heavy paper and glued on with an Elmer's Glue Stick. This Glue Stick idea came from Mike Peebles. Before Mike retired in 2020 he was the Elmer Osterhoudt of the 21st Century. I actually argued with Mike over this Glue Stick idea, saying it would never hold up. His final comment was, "I never had any trouble with it." I tried it, and years later I can also say, "I never had any trouble with it."
 
 
 
Here's a short video. It is just as boring as the previous video on Page 1.
 
 
 
Missing from the video is the local "flamethrower," WNPV AM 1440. Transmitting with 50,000 watts, this station came in so loud you could pick it up with a detector made out of a jelly donut and a piece of string. After serving the area for 60 years, it went off the air on April 30, 2020.

The station has five 165 foot antenna towers on 13 acres of land near the North Penn High School, in Lansdale, PA. Also on the site is the transmitter and a building housing the studio.

Just prior to the station closing, the North Penn School District, crying broke as usual, raised the North Penn area property taxes by 3.1 percent. This violated the 2.9 percent cap imposed by the state of Pennsylvania, but they just seem to do whatever they want. They weren't even holding classes at the time due to the virus. In July 2020 the school district found 2.3 million dollars in its coffers to buy the WNPV property.

This is a good thing, right? A high school with an actual radio station, not some collection of low power equipment connected to a wire antenna on the school roof. Think of the educational possibilities, and the fact that they could make it into a cool station that would rival the two college stations in Philadelphia, WRTI and WXPN.

Their plans are to demolish the station and use the property as an athletic field and a parking lot.
 
 
 

 
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