Modern Radio Laboratories ® /Alfred P. Morgan Mash-up

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Making the coils.
Taking the mystery out of what wire goes where.

Elmer Osterhoudt and Alfred P. Morgan both give instructions on how to wind the coils and both are hard to comprehend. Morgan advises to just buy the coils, but gives instructions on how to wind a coil on a Bakelite coil form.

Elmer wants you to follow the diagram on the left, drawn in typical MRL lo-res 2D. Are you going to buy blank coil forms and wire and try to wind a coil based on this drawing? Better just buy the coils already made from MRL. This lousy drawing is marketing genius.

The superior drawing in Morgan's book is still confusing. Above, on the far right drawing, pins 1 and 2 on the coil are closest to you. The circle in Elmer's drawing is the socket. If you mentally tilt the circle and compare it with the Morgan socket, "P" is pin 1.

To complete the confusion, if you have an antique coil or tube socket, the numbers on the socket won't match up with the numbers in the drawing. If I had never seen a real coil, I'm not sure I could make one based on these drawings.

This explains the guys who say, "I built one of these when I was 10 years old. I've spent my carrier in electronics thanks to Alfred P. Morgan."  When I was ten years old I connected a battery to a light bulb and was mesmerized, and these guys were building radios. I guess I should have read some of them thar Morgan learnin' books. Eventually, I did.

The coils are "standard" in the pin configuration. (The only reason I state this is that Morgan said to buy the coils, and if there wasn't some standard at the time, the radio wouldn't work.) A 1935 Bud Radio Products catalog states that their coils can be used in any circuit specifying a four prong coil, so this configuration dates back at least to 1935.

There are two small pins and two large pins. Logically, you'd think that the big coil would connect to the big pins and the small coil would connect to the small pins, but that's not the standard. Each coil is connected to a small pin and a large pin.

Elmer puts the tickler winding on the top, Alfred Morgan puts his on the bottom. It doesn't really matter as long as you wind the primary and tickler coils in the same direction.

The MRL coils wind upward, the Morgan coils wind downward. In other words, Elmer made a hole near the bottom of the coil form, pushed a wire through it and into pin 1. He then wound the coil up towards the top. Morgan did the opposite; he made a hole in the top of the coil form, pushed a wire through it and into pin 1, and then wound it towards the bottom.
A set of MRL coils.
A set of BUD coils from the 1920s.
Though both of these sets are color coded, there was no industry standard for the colors. The fact that the red (and possibly the green) coils are similar is either a coincidence, or Elmer adopted a color scheme from another manufacturer.

Here is MRL / Morgan comparison data for the AM Broadcast Band coils. Two coils are needed to cover the band.

  Primary Coil turns Wire
Tickler Coil turns Wire
COIL 1        
MRL 84 28 14 28
Morgan 70 30 20 30
COIL 2        
MRL 170 34 25 34
Morgan 150 34 45 34
Right away we see a discrepancy. Morgan uses less turns on the primary and more on the secondary. Osterhoudt tells us the first MRL coil will tune from 2100 kHz to 950 kHz and that the forms are 1.5" in diameter. The second coil tunes from 1000 kHz to 436 kHz.
The pin connections of the two coils (compare to the drawings). Wind both coils in the same direction. For example, if you wind the primary coil down from the top, starting on pin 1 and ending on pin 2, then also wind the tickler down from the top, starting on pin 3 and end on pin 4. Both coils must be wound in the same direction or the radio won't oscillate. Leave 1/8" between the two windings.

Markings in white are for the MRL coils.


  To wind the coil you need tension on the wire. This can be done by passing the wire through a hole in a clothespin (an idea from one of Elmer's handbooks).

Scrape the insulation from the end of the wire. Drill a hole in the top of the coil form, pass the wire through the clothespin, into the hole, and into pin 1.

Heat the pin with a soldering iron. Solder will wick into the hole, soldering the wire to the pin.

When the coil is wound, hold it in place with a piece of tape. Drill a hole, scrape the insulation from the end of the wire, and pass the wire through and into pin 2.

- Click on image -
After you wind the main coil, wind the tickler coil in the same manner. I found that trying to get the bottom tickler winding wire into pin 4 was almost impossible, due to how close the hole in the coil form was to the pin. Use this work-around:

After completing the coil, hold the wire in place with tape. Cut off enough wire to reach out of the top of the form. Scrape off the insulation at the appropriate spot, insert the wire into the hole and cause it to exit the top. Next, insert a piece of coil wire into pin 4. Push it up till it also exits the top of the form. Twist the two wires together and gently pull them out through the pin. Solder.
The completed coil. It tunes up to about 1100 kHz. A second coil is needed to tune the upper part of the AM band.

Let's make some old batteries.

Elmer said to use three 9 volt batteries in series for the B battery, so we'll make a box for them.
A paper box was made to test the template, which was drawn on thin cardboard.
The dotted lines have been lightly scored with the utility knife. This took most of a Sunday morning. I have a new respect for box designers.

While making this box, my back was hurting so bad I couldn't think straight. Two days before, I hurt my back while putting on my SOCKS. It felt like house current shot through my lower back. By Sunday I was in agony.

To make matters worse, my back seemed to be possessed and to want to incapacitate me. It was like, "Oh, did you get comfortable making your stupid little battery box? Well, take THIS!! And THIS!!!" as I became paralyzed in unbelievable torment.

"Do you need to cough? Cough gently, like a little girl. That's it, cak, cak, cak. I'm sorry, that sounded too much like a real cough. Take THIS!!" My back spasmed in blinding pain.

It took 15 minutes to walk 10 feet to the bathroom, and then the torture got worse, but will not to be described here. This went on for a week.


Connecting the batteries and finishing the box. At least I was productive, though I couldn't do much else at the time.


Battery box art was downloaded from the Internet and the motto changed to "Frodo Lives!" This
saying was made famous when it was found as graffiti in the subway of New York City in 1965.
Notice the battery on the right was manufactured in Lothlorien.

The batteries were from the Dollar Store, so this 27 volt battery cost $1.50. Elmer would be pleased. Why didn't he make MRL "B" batteries? He made everything else, and he sure made a lot of boxes.

This box will also hold four 10.5 volt microphone batteries and you'll have a 42 volt battery. (Excell A177, Duracell PC177A, Eveready E177, Energizer EN177A.) However, the batteries will set you back $22 plus shipping and the ghost of Elmer Osterhoudt will appear in your dreams. (If this actually happens, please let me know what he looks like.) The PDF file of the box is here.

Battery art can be found on a Russian site hosted in Canada called "Radio Nostalgia." I can't read it, but "radio" is spelled "радио." Most of the labels are in the "Unsorted" directory, here.


A 45 volt battery. $2.50 to make it yourself, $30.00 if you buy one from a "thief," as Elmer would say.

And now, without further adieu...
A demonstration of the radio. CAUTION: loud squealing ahead!

If you've enjoyed this, view MIKROWAVE1's Alfred P. Morgan One Tube Radio video. Part 1. Part 2.