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

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No.10 Pictoral
No.10 Schematic
The MRL catalog states that a 4.3 volt Mercury battery was furnished with the kit. The parts list also shows a 4.3 volt battery, as do the drawings above, so this is not a misprint. This battery was about the size of an AA battery and fit into the battery holder sold by MRL for AA batteries.
4.3 volt battery

1963 MRL catalog batteries
This entry from the 1963 MRL catalog shows Elmer sold 4.5 volt batteries, not 4.3 volt. In the 1972 catalog this battery isn't listed, but the catalog entries for both the MRL #18 and the MRL #10 state they are supplied with a 4.3 volt Mercury battery. Is it possible that the 4.3 volt batteries were just old 4.5 volt batteries?

An Internet search for a 4.3 volt battery, including old Allied Radio Shack and Lafayette catalogs, and data sheets from Eveready, Burgess, and RCA does not reveal a Mercury battery (or ANY battery for that matter) that was rated at 4.3 volts and resembles an AA battery in size.
Mercury Battery
This is a page from a 1966 Radio Shack catalog. The shape of the Mercury batteries look right, but they are off by 1/10 of a volt. There are ten types of Mercury batteries listed here, but in 1960 Radio Shack sold THIRTY-SIX types, and not one is rated at 4.3 volts. (Someone has set up a great site to view RS catalogs. Select the 1960 catalog and go to page 178 here.)

An MRL fan named Jeff Schmidt wrote in on the subject. He says a 4.2 volt can't be tweaked to supply 4.3 volts because the voltage arises from the choice of chemicals, not how much you use. To deepen the enigma, Elmer didn't sell them through the MRL catalog, they only came with the kit. Who made them, what did they look like, and what did you do when your battery went dead?

There are many modern mysteries, such as "Where is Emilia Earhart?," "Who was D. B. Cooper?," Did Paul McCartney die in 1966?," and the ultimate mystery of the Universe, "Why is there something instead of nothing?" Now we can add, "Where did Elmer get 4.3 volt batteries?"


tile cutting saw
This tile cutting saw was found in the trash two years ago. I walked it over a mile back to the house (it has wheels). My idea was that this would make a great small table saw, so I bought a blade and the bolt to hold the blade on. Unfortunately I found the whole thing is out of whack. I think it was either knocked over, or when they threw it in the trash, they THREW it in the trash. After an hour of messing with it I was able to cut some Poplar panels for the cabinet, so the saw wasn't a total waste of effort.
Cabinet Parts
Cabinet Parts
It's only a few pieces of wood, but slots are needed to hold the front panel. The slots are what the tile cutting saw was needed for.
Using screws, glue and tape to assemble it plumb and square using only my eyeballs guaranteed it would have neither of those qualities.
Cabinet Parts
Cabinet Parts
Actually, it came out pretty good. One side is off a bit in the back, shown on the right photo while it is upside-down. Nobody will ever notice.
MRL No.10 crystal set
MRL No.10 crystal set
I bought gray and slate blue paint. I painted it blue, then had second thoughts, so I removed the blue in a photo editor and put it up for a vote. Blue won. I only had two voters, other than myself, but one of them was my friend Joe, who didn't like the cabinet at all when he first saw it, and thought it should have been stained. I figured he'd be more objective.

The Radio Boys First Wireless
I think I liked gray because The Radio Boys first crystal set was gray in 1922.
The Radio Boys First Wireless
Shown here are Herb Fennington, Joe Atwood, and Bob Layton at the moment the very first signals came into their radio, an overture played by a "famous orchestra." Missing is Jimmy Plummer, who forgot his headphones and ran home to get them. Why did the author leave Jimmy out of this momentous scene? I wonder if it was because it was easier to have three people on the cover of the book, so you can see the radio better. It's also possible that Jimmy, also known as "Doughnuts," was fat and purposely wouldn't be included in the scene.

Why don't the headphones have headbands?

First radio of The Radio Boys
The Radio Boys first crystal radio. It looks impressive, though we can't identify the round things (knobs?) and the vertical lines across the top, even after enhancing the image. I guess the artist couldn't make it too precise, or your eye would go to the radio and not the Radio Boys.
Radio Boys mystery box
What kept me awake at night was wondering, "WHAT WAS IN THAT BOX?"
Eventually, the realization struck me that it was probably the headphones.

Here's a short video of the radio.

1 transistor amplifier
Note: Many small tube and transistor sets use the headphones as part of the circuit. When connecting to an amplifier (or using a piezo-electric or crystal ear plug) a 4.7K resistor must be used in place of the headphones to complete the circuit.

This concludes today's broadcast.