MRL No. 1

Modern Radio Laboratories®
No. 1 Crystal Set

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	- Elmer Osterhoudt Modern Radio Laboratories

This is a Modern Radio Laboratories No.1 Crystal Set that was built in 2020. The circuit was developed in 1932 by Elmer Osterhoudt.

The trademark "Modern Radio Laboratories" was granted on December 15, 1932.
The first MRL product was a "blue print" to build this radio.

Close-up of the wave trap. The coil and variable capacitor combination can eliminate a strong interfering signal.

The very first MRL advertisement. This appeared in the February 1933 issue of "Short Wave Craft."
For 25¢ you received a "blue print" of the MRL No. 1 crystal radio. The "blue print" was actually just a mimeograph copy of the plan.

It doesn't sound like you got much for 25¢, especially when you consider it was worth over five dollars today, but people must have sent in their quarters because it started a company that lasted for over half a century. As a matter of fact, in 1968 Elmer related that after he placed the ad above, the floor was covered with letters with 25¢ in them. This was in the middle of The Great Depression!

While researching Elmer Osterhoudt and MRL, it occurred to me there may be no one alive today who has ever seen an MRL No. 1 Crystal Set. There are surviving examples of the No. 2 set, which came as a kit, and was sold until 1986 when Elmer passed away. It was resurrected in the 1990s by Paul Nelson, who took over MRL. However, the No. 1 set was never sold as a kit.

The only way anyone was going to see one was to build one!

DP-26 MRL No. 1 Crystal Set

HB-17 MRL No. 1 Crystal Set

HB-17 - making the coil for the trap

The original "blue print" is lost to history, but fortunately Elmer Osterhoudt published the plans in two different documents several decades later. On the left is "Detail Print" number 26. In the center is a version of DP-26 found in Hand Book 17. On the right is the back page of HB-17, showing how to make the MRL "QRM" coil. Click on the thumbnails to view the plans.

Elmer said the value of C2 is important and is determined by your particular antenna. On the right it shows that Fahnestock clips are used so you can swap out different values.

The circuit is unusual. Normally in a circuit like this, the switch on the coil would short out a section of the coil. This circuit uses the full length of the coil at all times, but connects it to ground somewhere in the middle, depending on which tap you select.

Notice the numbers 8 and 9. These are explained further down, under the photo of the coil.

Turning the main coil and removing the QRM filter in the schematic shows what a simple design this is.

The same circuit from a MIDCO catalog in the 1980s. The kit from MIDCO cost $89.00 at the time.

If MRL sold the No.1 crystal set as a kit (as they did the No. 2 crystal set), it would look something like this. You would get all these parts and full instructions for about $1.80. The coils would be pre-wound and the front panel would have all the holes already drilled in it.

The $1.80 price seems low, but I derived it like this: The MRL No.2 crystal set has almost the exact parts count as the No.1, but without the "QRM" coil. The No.2 kit sold for $5 in 1973. $5 in 1973 was worth $1.54 in 1933. Throw in the QRM coil for $0.25 and you have $1.79!

Well, it's 2020. There was never a No.1 crystal set kit and Elmer Osterhoudt isn't around to order these parts from. It took weeks to gather these parts and they cost over $100.00. If I didn't already have the crystal and cat whisker detector, it would have been an additional $55. (They used to cost 19 cents.) The most difficult item to acquire was the vintage cloth covered wire, which came from ebay.

The switch points and lever were purchased in 2018 from Gary Schneider (RIP) on his website, "Play Things Of Past Medina, Ohio" (or "Playthings of the Past" as people called it).

Making a template for the front panel.

Making the template for the front panel took longer then I thought. The spacing for the switch points had to be more or less perfect. (It was probably perfect on the template but was less than perfect on the panel, due to my drilling. I had to enlarge two of the holes to slightly move two switch points.)

In all of Elmer's prolific writings, he always referred to the panel material as "Compo." The list of parts for this set says to use 1 Compo. panel 1/8" x 6" x 7". It took quite a bit of looking to discover "Compo." is Masonite. Apparently, "Compo." is short for "composition board."

1/8" Masonite is difficult to find for some reason, unless you want to buy a sheet 8 feet long! This panel is an "Ampersand Museum Series Hardbord Panel." (Notice the spelling of "hardbord.") I got it from "Jerry's Artarama," in a pack of three. They are 5" x 7" and came in a giant box. The box was so big I wondered what the heck I had ordered when I saw it. They sure were packed well!

UPDATE! Thanks to fellow MRL fan Vic Rodriguez, a perfect layout of the front panel is available in .PDF format here.

The coil forms had to be of a thin material, as any interaction of the coil with the form affects the performance of a crystal set in a negative way. These are made from a thin wrapping paper tube, 2 inches in diameter. The ends were reinforced and they were given three coats of polyurethane to strengthen them.

The coil was wound by hand and tapped in the appropriate places, per the instructions.
Elmer said to use "coil dope" to hold the ends together. I used Elmer's Glue-All. Different Elmer, same name.

NOTE: The schematic shows numbers 8 and 9. In the photo above, 8 would be on the left, 9 on the right.

Listing for the two coils, from page F-6 of the MRL catalog. It's actually called an "8-9" coil. This is one of those MRL mysteries. 1, 2, 3 and 4 are the connections to the QRM coil. What happened to 5, 6 and 7? We could possibly find out if an original "Blueprint" can be found.

I don't know what the correct method is to remove the cotton cover from the wire, but I picked it off with a utility knife and tweezers.
Under the cotton, the wire is coated with enamel. The enamel was scraped off, then the wire was tinned with solder.

Sloppy solder connections.

The QRM coil. QRM is "man-made interference." This coil is used with the left dial on the front panel to null or trap a station that is causing interference. It would be interesting to see how the original "blue print" described the making of this, since there was no "MRL QRM COIL" for sale at the time.

If you make your own, both coil windings go in the same direction, a fact that Elmer never mentioned. If you want to use those rivet type solder lugs, they are still available at MRL to this very day, which is where I got them. MRL WEBSITE

A fan of MRL named Victor Rodriguez pointed out that in some publications Elmer says to wind the large coil with 110 turns, and other times he said to use 105 turns. He said to use 15 turns space wound for the smaller coil, and he also said to use 20 turns close wound. He said to use cloth covered wire, but his later coils had enamel covered wire. The fact is, any of these combinations will work.

Headphone jacks. Every MRL radio I've ever seen uses the type on the left. They came in blue, yellow, orange, red, gray and black. However, I can't help but think these are post WWII and weren't available in 1932. I opted to go with the ones top-right. The brass shanks tell me they are really old.

Elmer said to use 1 inch Fahnestock clips for the antenna and ground. Do you know hard it is to find 1 inch Fahnestock clips?? Why do they need to be an inch? I found four of them. I polished two of them so they would look new.

The rear before wiring the set. The instructions say to wire it first, then add the main coil. One concession I had to make was to use modern variable capacitors. They actually look very much like vintage ones, but a little smaller.

The is no mention of a wooden base in the instructions. Upper-left, two Fahnestock clips are there to bypass the cat-whisker detector with a diode if needed. They weren't needed.

The Philmore crystal detector. I wasn't sure if they were made in 1932, and didn't know if the wooden knob was historically accurate for an older version.

It turns out that Philmore had been around since 1921, and even though some versions had a Bakelite knob, the wooden version is fine.

The drawing of the front panel compared to the actual front panel. The drawing is from DP-26.

Here is capacitor "C2" mounted in its Fahnestock clips. Elmer has this positioned behind the coil, and it is difficult to reach. Once you select the right value you don't have to touch it again, but it's frustrating to swap out.

How well does it work? Below is a video of a quick test. It was done in the morning of July 2, 2020. The location is about 15 miles NE of Philadelphia, PA. It logged four whole stations!

Actually, I think it works very well for a simple crystal radio. It wasn't designed to be selective, yet the stations are fairly spread out across the dial.

View here or on YouTube:

The radio needed a label to identify it. I was going to make an elaborate one, but Elmer would never have approved it.

Next, a MRL number 2-A set!