According to the caption of this picture from the June 1929 issue of Popular Mechanics, the gentleman shown above is merely “sick.” But he doesn’t look very good, and we suspect he may have already succumbed to electrocution.

He wanted to listen to the radio, but they didn’t want to drag the radio into his room. Nor did they want to run any wires. So someone came up with the bright idea shown here. There was already a perfectly good set of wires in place, namely, the house electric wiring. So they decided to put it into service by feeding the radio output into the power wires, and plugging in a set of headphones on the other end. A 2 μF capacitor was put in place as a gesture toward safety.

The first problem seems to be that it wouldn’t really work. Whatever audio made it through would be drowned out by the 60 cycle hum, assuming that the lighting current was AC, which it was in most of the country by that time.

And unless my back-of-the-envelope calculations are wrong, the capacitor will have a reactance at 60 Hz of only about 1300 ohms, meaning that a current of up to 90 mA could still flow through, which seems like plenty to deliver a lethal shock, especially if you’re placing the electrodes right next to the brain.

So in our estimation, this project is not one which should be attempted.  Kids (and adults):  Do not try this at home!

Seventy five years ago this month, the June 1944 issue of Popular Mechanics carried a lesson in the now almost forgotten art of reading a vernier scale.  With virtually any kind of instrument with an analog display, such as a caliper or micrometer, the vernier scale allows the human eye to make a much more precise reading.

The vernier display consists of two scales.  In the example shown above, the top scale is the main scale, and shows just over 5.3 inches.  (The zero on the bottom scale takes the place of the pointer which would be used on a non-vernier scale.)

The human eye, looking at this pointer, would undoubtedly conclude that the actual measurement is 5.35 inches, since the pointer is about halfway between the 3 and the 4.  But is it really 5.35, or is it 5.34 or 5.36?  You can’t really tell with the naked eye.

But the vernier scale makes eyeballing it easy.  You simply look at the bottom scale, and see which number is exactly lined up (or most closely lined up) with a number above.  In this example, the 6 on the bottom scale is lined up exactly with the 9 on the upper scale.  The number on the upper scale is not important–it’s only important that some number on the lower scale is lined up exactly.  In this case, the 6 means that we add 6/100 inch, meaning that the exact measurement is 5.36″.

Below, we see a vernier dial applied to a caliper.  In the picture on the right, the scales are flattened so that they can be viewed on the printed page.  The idea is the same.  The sleeve scale shows 0.3 inch, plus 0.12 on the thimble scale, since the center line is between 12 and 13.  The 5 on the vernier scale is lined up with the 20, meaning that we add .005 inch.  Thus, the measurement is .3 + .012 + .005 = .3125 inches.

Radio fans are probably most familiar with the “vernier dial” shown at the left.  This one is available on Amazon and is called a “vernier dial.”  However, the vernier markings which are supposed to be on the tab on top are inexplicably missing.

The vernier scale is named after vernier acuity, the human eye’s ability to detect small differences in the alignment of a straight line.

Eighty years ago this month, the May 1939 issue of Popular Science carried the plans for this two-tube set, which was said to “bring in London, Rome, and Berlin as easily as local broadcasts.” The circuit was very efficient, since the two 6C6 tubes ran on a B+ voltage of only 3 volts for shortwave, or 1.5 volts for standard broadcasts. The tubes, although nominally 6-volt filaments, used 3.4 to 3.8 volts, as adjusted by the 10 ohm rheostat.

For those desiring a slightly different radio experience, the same magazine also showed how to put together this three-tube “dressing table radio” concealed within a Marie Antoinette doll. The radio itself is concealed under Marie Antoinette’s dress. Atop is affixed a ceramic figurine. While the exact replacement is apparently no longer available, this Marie Antoinette salt shaker would undoubtedly work perfectly:

This picture of the HCJB transmitter site at Pifo, Ecuador, appeared in the May 1959 issue of Popular Electronics. The magazine noted that the station was currently capable of transmitting on a single shortwave frequency with 50,000 watts, but would soon have the capability of transmitting on two frequencies simultaneously at 30,000 watts each.

For more information about the station, see our earlier post about the station’s history.

This was by no means a new idea at the time, but the May 1979 issue of Popular Electronics shows a simple way to boost your line voltage. It employs a six-volt filament transformer wired so that it becomes an autotransformer, and the voltages on both coils add. So if you start with 120 volts, you wind up with 126. As the accompanying text explains, you might need to use some trial and error. If you wire it up and the voltage goes down by six volts, then you need to reverse the secondary windings.

While they are not common, 6 volt filament transformers are certainly not unobtainium, and you can get them from Amazon at this link:

If you need a slightly heavier duty version already assembled, then you can’t go wrong with an adjustable autotransformer (commonly known as a variac) like this one:

The May 1934 issue of Short Wave Craft magazine included this ad for the “Scout,” a one tube shortwave set from the Try-Mo Radio Co., Inc., of 85 Cortlandt Street, New York.  The set sold in kit form for only $3.95, but the type 230 tube, batteries, and headphones would run an additional $4.25.  The set came with plug-in coils for shortwave, but a coil for the standard broadcast band would cost an additional 39 cents, probably a good investment in case the short waves were quiet.