Modern Radio Laboratories
No. 10 All Wave Crystal Set
(Replica of the MRL No. 10 kit designed by Elmer Osterhoudt)

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MRL switch points were approx 5.5mm in diameter, probably 3/16".  Using a piece of black poster board, I was able to try different screw types to replicate the rivets Elmer Osterhoudt used. On the right are "Chicago screws." These look pretty cool, but not for this radio. They're a little too big, but will look great in another radio.
A closer view of the Chicago screws. On the right are 6-32 flat head screws.
I also tried 6-32 brass flathead screws, but they still looked like screws! Then a fellow MRL fan named Vic Rodriguez wrote to me and said, "Mike try these threaded rivets." and sent me a link to a place that has parts to restore vintage cars. They looked great! (This photo shows them on the poster board.)

Naturally, I selected the wrong ones the first time and had to wait another week for the correct ones to arrive. If you're interested, the part number is NUT250, 3/4" truss head.

MRL Switch Points
If you're wondering where I got the idea to use screws, take a look at this. When actual switch points became impossible to get, MRL substituted 6-32 flathead screws. These are from 1984.

NOTE: The label on the envelope is obviously an address label, but who typed it? The address label company? MRL is spelled "Mrl." (with a period) as in "Mr." or "Mrs." Was this addressed to Mister Switch Points (and family)?

Here are the connections on the back of the front panel. I had to cut the length of the screws down.
Elmer would never have done it this way. This is a hundred times more expensive and time consuming than using actual rivets.
Switch Points and coil
The switch points connected to the coil.

Modern Radio Labs Crystal Set
This MRL radio uses screws as switch points. This thing looks ancient, and it appears to be a No. 2 with an extra switch, but what the extra switch does is a mystery. How old is it? The MRL style switches date this to after 1952 and the screws date it to even later. The coil has fibre rings on the ends and the wire is cloth covered, dating it to 1975 or earlier. So the best guess is that it was built no later than 1975.

All your base are belong to us

Radio Base
The plans for the No. 10 call for everything to be mounted on the front panel. I don't see the logic in this. How do you operate the radio with nothing to hold it up? You can't lay it on the table, and you're not going to hold it in your hand, so it needs a base. In that case, the heavy variable capacitor and the batteries will be on the base. The plans call for a 4.3 volt Mercury battery. I used two AAA batteries. I would have used three, but I only had two vintage battery holders.

A modern 4.5 volt battery could be used, but the plans don't show how the battery is connected; it appears it was soldered in. The heck with that.


Masonite front panel
Vic Rodriguez, the guy who sent me the link for the threaded rivets, mailed me three blank panels. I told him I don't have an easy way to cut a panel so it comes out square, and the panels arrived in the mail a week later, cut to the proper size. As the Radio Boys would have said in 1922, "He's a regular fellow!"

I made a paper template, then pushed an ice pick through the paper and into the panel to mark it. It took hours to make the template and panel. I kept thinking that if I could buy the kit, Elmer would have already done all this work. How did he do it? I bet he had a drill press and drilled through ten at a time.

panel and base
The panel and base before assembling. The areas masked from the paint are so wood glue could be used to strengthen the connection.

Front panel and base
The coil is mounted last.

MRL no. 10 layout
It seems the original panel was carefully planned, but the volume control knob is floating out in the middle of nowhere. It has no dial scale or label to identify it. By moving the control down, the panel can be made more symmetrical. I mulled this over for a day. If I moved the control, the radio would closely resemble the MRL No.2 set. On the other hand, this is where Elmer Osterhoudt thought it should go, for whatever reason.
MRL crystal set
MRL no.10 crystal radio
  Should I make it look like Vic's MRL No.2 reproduction?   Eventually I figured that if Elmer thought it should be there, I'll leave it there.


One Transistor Amplifier
One Transistor Amplifier
Here's the little one transistor amplifier. The transistor is a vintage PNP type. In the plans, Elmer states that a 470K resistor is supplied with the kit but you may have to change the value if you use a different transistor, all the way down to 22K. I had no idea what transistor Elmer used, or even what transistor I used. How are you supposed to know which resistor is the correct one? The only way to find out was to build the circuit and try different values. It turned out that 330K worked better than 470K for this particular transistor.

The odd thing is that the amplifier worked with NO resistor.

This modern capacitor wasn't going to look right, so it was stuffed into an antique casing.


Fahnestock clips
Fahnestock clips
The plans call for 1/2" Fahnestock clips to mount the diode, which is what I used, only to notice the screws were too long the depress the clips. After searching for "the perfect screws" I gave up and went to 3/4 inch Fahnestock clips. These are easier to work with, anyway.

The diode is a 1N34A manufactured in March, 1960 by Kemtron. Kemtron was located in Newburyport, MA, but not much else is known about the company. The plant was demolished in 1981. According to The Transistor Museum, "Kemtron diodes are truly unique."

So at least the radio has that going for it.

1949 Popular Science
How well does it work? Do sparks shoot out of the headphones?

It works!!
 IT WORKS!   It's a crystal set. It works like a crystal set.
With the one transistor amplifier, it works like a very good crystal set! Since this is the "city" version and I have a crappy antenna, I didn't expect too much, but was pleased that the few local stations (within 10 miles) came in with very good volume and were easy to separate from each other. At the upper end of the coil I heard several shortwave stations, including CHU Canada on 3.33 MHz.

CHU transmits from Ottawa, Canada and is 450 miles from this location, which is near Philadelphia, PA. Stating "I heard it" does not mean it can easily and reliably be dialed in on a crystal radio. However, the fact that this crystal set can pick up shortwave is somewhat amazing.

Detector Stand
The control to switch from the diode to the crystal stand comes in very handy. You tune a station with the diode, then switch to the stand and find a "hot spot" on the crystal. The crystal can sometimes make the radio tune sharper, or at least seem to. I think it's cool that you can pick up radio signals with a piece of a mineral, so I use the stand.

Vic Rodriguez sent me enough fine catwhiskers to last me the rest of my life. That's "fine" as in thin. In this photo a piece of fine catwhisker has been wrapped around the heavy one.

I was halfway done wrapping the wire when I realized I had stumbled onto a fantastic new invention. The DUAL CATWHISKER! I gazed at it in awe. It glowed in my quivering hands like one of Tolkien's Silmarils. I'll be RICH!!
Dual Catwhisker
The DUAL CATWHISKER in use. (pat. pending) Yes, I'll be rich, I tell you!
I'll market it as "Mighty-Fine" since nobody has ever used that name before.

Battery Skins
MRL sold Burgess Batteries. The AAA batteries were "skinned" to make them look like Burgess.
Speaking of batteries....