In theory, nothing could go wrong using this simple crystal set from 60 years ago, from the February 1956 issue of Popular Electronics.  As the photo makes obvious, it’s a simple crystal set that uses the house wiring as an antenna.  It has no tuned circuit, so it simply pulls in the strongest local station.

The circuit is isolated from the line by a .01 uF disc capacitor. A disc ceramic rarely fails, but one failure mode is a dead short. The article warns “do not omit the blocking capacitor under any circumstances.” It also points out that all of the internal wiring should be taped over or covered with spaghetti tubing. Only one blade of the plug is used, so presumably, even if the capacitor shorts out, there’s no immediate risk of electrocution.

But just to be on the safe side, the article also warns that you should “observe the same precautions in using this crystal receiver as when using the common a.c./d.c. household table radio. Don’t hold it while standing on damp basement floors, handling water faucets or gas stoves, or when taking a bath.”

Of course, if you’re using this set in an emergency when the power is out, I guess you’re OK.  But you still want to observe all of these precautions, because eventually the power will be back on.

Seventy-five years ago today, this high-quality radio-phono was under a hundred dollars (with trade in of your old radio), at Gimbles Department Store in Milwaukee. This add appeared in the January 31, 1941, edition of the Milwaukee Sentinel.

The set came in a deluxe mahogany cabinet, and featured world-wide reception (presumably meaning that it tuned both standard broadcast and shortwave).  The automatic record changer would accomodate up to fourteen records.  It also had a “built-in antenna and ground.”

75 years ago this month, the January 1941 issue of QST contained the plans for two one-tube transmitters, both using the recently introduced 117L7GT tube. The tube was ideal for a simple transmitter, since the filament ran directly off line current, and the envelope contained a rectifier and beam-power tetrode. Thus, the set could operate directly off line current, with no transformer required. The set shown above was made by R.T. Lawrence, W8LCO, of Dayton, Ohio. The schematic below is the similar set made by Keith Hayes, W9ZGD, of Milwaukee, Wisconsin.

Either set could be easily reproduced, with minimal part substitutions, from readily available components.  It should be noted that neither of these transmitters has much in the way of output filtering, so it would probably be necessary to add an output filter to comply with modern regulations.

In his article, W9ZGD reports what many modern QRP’ers have rediscovered:

Although 4 or 5 watts doesn’t sound like much input, it is surprising what one of these little transmitters will do, particularly to one who has never tried anything like it before. Possibley, according to tradition, I should list the stations worked but, since the antenna, receiver and operating ability affect the statistics as much as the transmitter power, I’ll just mention the fact that 5 watts give a signal about one “S” point lower than 20 watts and 2 “S” points lower than 80 watts. And, anyway, it’s more fun to fish with barbless hooks!

The W8LCO QSL card shown here is from the builder of the transmitter shown at the top of the page. The QSL was for a contact a few years earlier, in which he reports running 24 watts input.

Fifty years ago, you would probably be the only one on your block with a computer if you built one of these. The January 1966 issue of Electronics Illustrated contains the plans for building this analog computer, suitable for addition, subtraction, multiplication, division, squares, and square roots.

Each dial is calibrated from 0-10, and there is a small ammeter.  For an addition problem, you set the switch to +/-, and adjust the two left knobs to show the numbers you want to add.  Then, you adjust the right knob until the meter is at zero.  Subtraction problems are done in the same fashion, except you set the right knob to the larger number, the middle knob to the smaller number, and the answer is shown on the left knob when the meter reads zero.  A similar procedure is used to do multiplication and division.  In the image shown above, the computer confirms that 5 times 4 does indeed equal 20.

For squares and square roots, a second section of one of the dual potentiometers is used so that both have the same resistance.  That dial shows a number, and the dial on the right shows its square.

The article points out that the device is basically the electronic equivalent of a slide rule (and probably much less accurate).  And like with a slide rule, you were on your own when it came to figuring out where the decimal point went.

I do remember in the elementary school library a book showing a similar contraption, which was wired up only for addition.  Instead of having three potentiometers and a meter used only for zeroing, it had two potentiometers and a meter from which the answer was read.  Despite thinking about how much easier that would make my math homework, that setup was probably much less accurate than the one shown here.

Shown here are simplified schematics showing the circuit used for addition and multiplication.  The combined wiring diagram showing the switches is, of course, also included in the article.  But the simplified diagrams give a good idea of how the thing works.  Both merely take advantage of Ohm’s law.  R1 and R2 are one tenth the value of R3.  As might be guessed, the parts list calls for linear tapered potentiometers.

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