Yesterday, we showed this puzzle from the April-May 1968 issue of Radio TV Experimenter magazine. The question was simple enough–you had to figure out the net resistance between two opposite corners.

Fifty years ago, hobbyists encountering this problem probably started out the way I did, by scribbling the diagram on a piece of paper, trying to flatten it out, and then realizing that the standard equations for series and parallel resistors weren’t really of much help, since they were all hopelessly interlinked.

Fifty years ago, the reader had to wait two months for the answer, as shown here in the June-July issue. So I suspect that more than a few got twelve identical resistors, made them into a cube, and then measured.

I didn’t have to do that, because today we have that Google thingie, and I found this solution to the problem, as well as the video shown below, which takes a slightly different approach.

The key to solving this is to notice that the voltage reading at all three of the points marked “A” is the same.  And the voltage reading at all three of the points marked “B” is the same.  This is because the diagram is symmetrical, and a current flowing from the left to any of the points A is going to pass through an identical resistance.  And a current flowing from the right is going to pass through an identical resistor to get to any of the points B.

Since the voltage reading is the same, we can go ahead and make a direct connection between all of the A points, and another direct connection between all of the B points.  Since the voltages are the same, no current will flow, and there will be no effect on the circuit.

The effect that it will have, however, is making the problem a lot easier to solve.  At this point, we have three resistors on the left, all in parallel.  We have six resistors in the middle, all in parallel.  And we have three resistors at the right, all in parallel.  It’s easy to compute that the equivalent resistances are 1/3, 1/6, and 1/3 ohm.  And those values are in series; so we just add them up, and the answer is 5/6 ohms.

This video takes a slightly different approach to arrive at the same answer:

Today we offer a deceptively simple looking puzzle, taken from the April-May 1968 issue of Radio TV Experimenter magazine.

The question is simple. This cube is made up of 1 ohm resistors on each edge. What’s the net resistance between two opposite corners? The answer will appear here tomorrow.

The man sneaking through the window isn’t a burglar. It’s a radio salesman trying to get a radio inside the house, where it can sell itself! The illustration appeared in the April 1938 issue of Radio Retailing in an article explaining how to sell.

The article explained that your canvassers can’t sell radios at the door, and they can’t get inside the door, because the homeowner is well aware that they’re just trying to sell.  And even if they do get inside, they’re not going to sell any radios armed with photos.

So to sell radios, the canvasser needs to stop trying to sell radios.  Instead, they needed to figure out a way to get a radio inside the house, where it could sell itself:  “The answer is to GET THE RADIO IN THE HOUSE.  And when I say get the radio in the house, I mean get the radio in the house by any lawful means at your disposal.  By trickery, by cunning, by anything under the sun but a hint that you want the lady to buy it.  By misrepresentation, if you will, provided you stick to your original story, even when you go back to sell.”

The article even advised having the boss go back to close the sale, rather than having the original salesman.  After all, the original salesman will go to great lengths to stick to his story that he’s not trying to sell anything.  The boss, on the other hand, has a bit greater aura of importance, and can probably close the sale.

The article speculated that if the original salesman handles both ends of the transaction, then he’ll probably place 100 radios and sell 80 of them.  On the other hand, he could place 500, of which 250 are ultimately sold.  The smart dealer figured out which system was better.

Eighty years ago this month, the April 1938 issue of Popular Science carried the plans for two interesting one tube receivers, the first of which is shown above.  This set was billed as being ideal for an auxiliary set in the kitchen, den, or child’s playroom, and would give good loudspeaker reception on local stations with an efficient antenna.

While the article pointed out that it might not have been the first ever one tube loudspeaker set, it was “perhaps the first time that those results have been achieved without incorporating complicated and tricky hook-ups in the design.”

The set accomplished this by using a new dual tube that had been on the market for a few months, the type 19.  The circuit used half of the dual triode as a regenerative detector, with the other half amplifying the audio enough to drive the speaker.  The set was built in a homemade wooden cabinet.

The other set featured in the magazine was more of a novelty, a vest pocket set about the size of a pocket flashlight, shown above.  This one-tube set was said to give excellent earphone volume on stations within 75 miles, allowing it to be a handy radio companion for the hiker or cyclist.  The filaments were powered by flashlight batteries, with a small 45 volt battery supplying the B+.  It used a type XSG “ultra-midget” tube nestled carefully inside the fountain pen case.

This compact but well equipped ham station from 70 years ago is shown on the cover of the March 1948 issue of Radio News.

The unidentified station features the control for the rotary beam, Hallicrafters SX-43 receiver, a wire recorder, Hallicrafters HT-18 exciter, and panadapter.  Not shown is the remotely controlled BC-610E transmitter being driven by the HT-18.

The March 1948 issue of Radio News carried the plans for this two-tube transmitter for 40 or 80 meters, ideal for portable or emergency use.

The author noted that most ham transmitters weren’t suited for such purposes due to their size, weight, and inflexibility of power supply. This “MiniTran” was built with those constraints in mind. The author settled on a two-tube design after difficulties with keying a one-tube design were encountered, especially with makeshift equipment. The circuit uses a 6C4 Pierce Oscillator driving a 6AQ5 output.

The circuit required 6 volts for the filaments, and 300 volts B+, which could be derived either from a vibrator power supply, or simply by tapping into the receiver’s power supply.

When the author got the rig on the air, he made a contact with the first station called on 40 meters, which was a contact with Tennessee from Connecticut. In the next week, seven more states were worked on 80 and 40, with reports as high as RST 589X.