Eighty-five years ago this month, the October 1941 issue of Radio News showed how to build this compact transmitter for 10-160 meters. Band switching was accomplished with plug-in coils, and input power was about 8 watts, and it operated AM phone as well as CW. The large component in the center was the modulation transformer. A voltage-doubler circuit was used, eliminating the need for a power transformer. The 6J5 served as Pierce oscillator, with the 25B6G as amplifier. The other two tubes handled the modulation.

Since it was an AC-DC circuit, the article warned that the chassis should not be grounded.

One hundred years ago this month, the October 1926 issue of QST showed how to build this receiver covering 12 through 20,000 meters. That works out to 15 kHz to 25 MHz. Band shifts were accomplished with plug-in coils, and the article contains full coil information. The article noted that the scale of the capacitors needed to be entirely different on both ends of the range. While a 125 pF capacitor would work well at 20 meters, it would be useless at the low end. On the other hand, a 625 pF capacitor would be useful at the low end, but impossible to tune at the upper range. The solution was to use a ganged tuning capacitor, with the two sections placed in parallel when needed, by use of the low-loss switch shown at right.

The basic circuit used one tube as regenerative detector, with two stages of audio amplification. Since hams were at 200 meters and down by this time, the author told about what signals could be heard on the longwaves in those days:

Who’s Who

Unless you have kept track of communication in bands other than the ham ones for the past few years you may miss out on a lot of things because you are not listening in the proper place. The broadcast band is pretty well known. Ship calling, answering, SOS work and messages relating to traffic handling occur on 600 meters. Actual traffic between smaller ships and land occurs on 660, 731 and 874 meters. The radio compass wave is still 800 meters. On 952 meters the government has a wave where a number of naval vessels and naval land stations can be heard batting them off hour after hour. Radio beacons (those things making bunches of dashes and never signing) are found on 1,000 meters. Then come the intermediate waves where high power land stations work high power ships. These waves are around 1052, and 1578 to 2499 meters. In this band will be found the high power tube stations WCC, WSH, WAX, KPH and so on, working the large liners. An other band from 2499 to 3156 finds only government stations, among them being the ever faithful NAA on time ticks, weather, hydrographic information and press. NAA’s time still comes off at 10 P.M. (E.S.T.) followed by an hour of weather and press start ing around 11 P.M. NSS sends time at the same time as NAA and follows this immediately (usually) with press. Lately NKF has been sending time ticks with the rest on 74 meters although it is understood that this is an experimental time service and may be discontinued. At around 11:15 P.M. WSA sends press on 650 meters, spark, and WSLI on about 2400 C. W., both stations being keyed from the same source. On 2200 meters WCO sends press at 9 A.M., 5 P.M. and at 12:18 A.M. WRQ starts his press on 18505 meters.

These are only a very very few of the hundreds of stations operating regularly on waves between 600 and 18,000 meters. After you have listened in on these waves for a little while you will find there is a great kick to be had from jumping from one station to another. The 600-meter kick alone is worth the candle!

Eighty-five years ago this month, the much of the October 1941 issue of Radio Retailing highlighted the prewar FM band, which covered 42-49 MHz. Well they didn’t call it by that name, but that’s how it came to be known after FM’s postwar move to 88-108 MHz. This map shows the coverage areas of current stations (solid circles) and stations under construction (shaded circles).

Eighty years ago, there was still a shortage of tubes. But if the tube in question was a rectifier, then the serviceman had a solution to the problem, namely, the selenium rectifier. This ad from Federal appeared in the September 1946 issue of Radio Retailing. It noted that even though the selenium rectifier was cheaper than a tube, it would actually last longer.

If you need to replace the selenium rectifier in an old circuit, you can probably do a better job with silicon diodes.  But if you want to keep the original look, like anything else, you can find NOS (new old stock) selenium rectifiers on eBay.

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If you do any electrical work around the house—or even if you don’t, and you just want to make sure the electrician did things right—you really ought to have an inexpensive outlet tester in your toolbox. You can plug one in and tell at a glance whether the receptacle is wired correctly, or if there is some invisible and potentially hazardous fault hiding behind the faceplate.

Those errors can include reversed polarity, an open neutral, a missing safety ground, or a hot wire that’s not hooked up at all.

Fifty years ago, fifty-cent molded plug-in testers weren’t sitting in blister packs on the counter of every hardware store. If a home handyman or experimenter wanted one, he often had to build it himself.

The circuit shown here appeared in the September-October 1976 issue of Elementary Electronics. As you can see, the design is deceptively simple.  It uses three neon lamps (NE-1, NE-2, and NE-3), each in series with a 100kΩ current-limiting resistor, bridged across the three conductors of a standard grounded three-prong plug:

• NE1 (Green) is connected between Hot and Neutral.
• NE2 (Red) is connected between Neutral and Ground.
• NE3 (Orange) is connected between Hot and Ground.

When plugged into a correctly wired 120-volt receptacle, line voltage is present across Hot and Neutral (lighting the green lamp) and across Hot and Ground (lighting the orange lamp). Because Neutral and Ground are tied together back at the service panel, there is zero potential between them, leaving the red lamp completely dark.

If you see the red lamp light up, or if one of the others fails to illuminate, you know immediately that something is miswired.  If you want to build your own, it’s a quick weekend bench project using a handful of NE-2 neon lamps, three 100k ohm resistors, and a replacement 3-prong plug.

Of course, these days you don’t have to warm up the soldering iron just to check your wall outlets. You can pick up a ready-made commercial receptacle tester for just a few dollars. Modern versions use the exact same three-lamp bridge circuit inside, though most also include a built-in push button to test GFCI outlets.  And, of course, unless you happen to have the parts in your junk box to start with, the cost of the commercial product will probably be a lot less than what you would have to pay to build your own. By the way, the colors of the neon lamps are not necessarily standard, so the color code shown in the 1976 version probably won’t match up with the modern product.

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