Monthly Archives: April 2019

1949 Two Tube Broadcast Receiver

Seventy years ago this month, the April 1949 issue of Popular Mechanics showed how to put together this simple two-tube broadcast set. Running off AC power, the set would drive a loudspeaker. It used many of the same parts as a one-tube set published in the January issue, allowing the radio student to upgrade the simpler set.

A 6J6 dual triode carried out the RF duties, with a 6AK6 pentode AF amplifier driving the speaker. The set employed a selenium rectifier.

One unobtainium part is the permeability tuner, similar to the one used in a 1948 Popular Science receiver.

Milwaukee Radio Listings, April 10, 1944

Here’s what was on the radio 75 years ago today. These listings appeared in the Milwaukee Journal, April 10, 1944 and show programs for April 10 and 11. (You can click twice on the image above for a larger version.)

Wartime Tube Substitutions

During World War II, many radio tubes were unavailable, and the magazines were full of ideas on how to cope. The April 1944 issue of Popular Mechanics showed how to make adapters to use similar tubes that might be available, but used different base types.

In particular, the magazine pointed out that loctal tubes were often available. Therefore, the adapter shown here allows a loctal tube to be plugged into a standard octal socket. The bottom half of the adapter was a defunct tube (probably the one being replaced), and the top half was a socket to match the new tube.

Eclipse of April 8, 2024

2024 Eclipse Path. NOAA image.

As we did in 2017, OneTubeRadio.com will provide full coverage of the April 8, 2024, total solar eclipse.

This is exactly five years from today. Little preparation is needed at this point, but you should make a mental note to travel to the path of totality, which is less than a days’ drive from most of the United States. The total eclipse will be visible in parts of Texas, Oklahoma, Arkansas, Missouri, Illinois, Indiana, Ohio, a tiny piece of Michigan, Pennsylvania, New York, Vermont, New Hampshire, and Maine. The path of totality also passes through Mexico and Canada. Major cities in the path of totality include Dallas, Little Rock, Indianapolis, Buffalo, Cleveland, and Montreal.

The eclipse will take place on a Monday. For the 2017 eclipse, we made our hotel reservations about a year in advance, and paid the normal rate with plenty of availability. So if you plan on booking in April 2023, you should have many options. Also, in late 2023 or early 2024, you should order your eclipse glasses.

If you have kids who will be in school, plan on taking them out of school that day. Unfortunately, the 2017 eclipse showed that American schools had an irrational fear of the eclipse and actively prevented children from witnessing it. If you believe that your child’s school is more enlightened, then on the first day of the 2023-24 school year, you should have your children ask the science teacher if the school is planning a field trip to see it. If the teacher balks, then your children should let him or her know that they will be absent the day of the eclipse.

This is an entirely reasonable request for most schools. For example, students in Chicago could be placed on a school bus and taken to see the eclipse only a couple of hours’ drive away in Indiana. The expense will be less than other field trips taken to amusement parks, movies, etc. This is true for schools in many cities. They have the opportunity to let the kids witness an amazing scientific event, but only if they do some basic planning.

But I predict that this won’t happen, since most schools won’t think of the possibility until after it’s too late to make the necessary plans, or they’ll have the same irrational fears that showed up in 2017. It’s the duty of the students to pester the administration so that the necessary plans are made sufficiently in advance. And as I explained in 2017, if the school fails to act, then it’s reasonable for children to skip school on April 8, 2024.

Diozo Phone Disinfector, 1909

A hundred ten years ago this month, the April 1909 issue of Popular Electricity carried this ad for the Diozo Phone Disinfector, produced by the Parker Chemical Co. of 233 Market Street, Chicago. (The address no longer exists, since Market Street disappeared and became part of Wacker Drive.)

The ad, confirmed by scientific tests, warns that the mouthpiece of every telephone swarms with malignant germs, including tuberculosis, diphtheria, typhoid, or pneumonia. There might even be more revolting diseases lurking there! Fortunately, to avoid the harm, all you need to do is slip the diozo phone disinfector on the mouthpiece. Diozo is apparently a disinfectant that works in its solid form to somehow kill germs.

But according to this article published just a few months later in the California State Journal of Medicine, the State Hygenic Laboratory (of California, presumably) questioned some of the claims made by the company. After being challenged, the company noted that to be effective, the Diozo must be crushed and mixed with water, which would make its use on a telephone somewhat problematic.

Strangely enough, the Diozo Phone Disinfector doesn’t appear to be available today. But if you search Amazon for “phone disinfector,” you can chose among the following products:

Homemade Hygrometer (Humidity Meter)

For the student looking to put together a classic science fair project from the past, this hygrometer from the April 1944 issue of Popular Science should fit the bill. A hygrometer is simply a device to measure humidity, and this one uses a single human hair as the sensor, just like the first one constructed by Horace Bénédict de Saussur in 1783.

Construction will require a bit of trial and error, but is quite simple. First, a strand of hair about four inches long is washed “in cleaning fluid.” Another set of plans available on the internet recommend the use of dilluted rubbing alcohol, which should probably work as the cleaning fluid. The idea is to remove the oil from the hair to make it more sensitive to changes in humidity.

One end of the hair is attached to a fixed point, and the other end is wound around a large-eyed sewing needle. The 1944 article recommends attaching it to the needle with sealing wax. However, you should be able to use other fancy stuff, such as hot glue or possibly just regular glue.

The needle is held in place by bearings consisting of shirt buttons. Finally, a pointer is attached to the needle. As the humidity changes, the hair expands and contracts, which causes the needle to rotate. The amount of rotation is visible on the pointer.

The First Sign of Spring

Eighty years ago this month, spring had sprung, and the cover of the April 1939 issue of Radio Retailing offered the reminder that a sure sign of spring was broken antennas. It was time to get out and fix them, and hopefully put a few dollars in the dealer’s pocket.

1919: Hurling a Man to the Moon

A hundred years ago this month, the April 1919 issue of Popular Science carried this image of a hypothetical traveler to the moon. The accompanying article detailed the problems of getting there. For example, balloons or airplanes were out of the question, since they both relied upon the atmosphere for their lift. A gun was a theoretical possibility, but the article pointed out that the Earth’s escape velocity was 26,000 feet per second. But the most powerful gun at the time had a velocity of only 5500 feet per second. The article correctly predicted, however, that there was a “ray of hope in the sky-rocket.” The article reminded readers that, contrary to popular perception, a rocket did not rely upon pushing against the atmosphere. Therefore, it would work in space.

Robert Goddard had already begun his experiments, but his name was not known in 1919. The only rocketeer mentioned in the article was stuntman Rodman Law, shown at left boarding a rocket for a test flight. The article notes that the flight was a spectacular failure, although Law survived. Ironically, Law died later in 1919 of tuberculosis.

It’s easy to look at an old article and laugh at the naivete of the authors. But they got the basic concept right: Yes, indeed, it is possible to get to the moon with rockets, and we did exactly that a half century later. Ironically, we are once again a half century removed from being able to go to the moon. Many readers of the 1919 article lived to see Americans walking on the moon. Sadly, that might not be the case for readers in 2019.

1939 One Tube Regen

Eighty years ago this month, the April 1939 issue of Popular Science showed how to put together this simple one-tube regenerative receiver.

The set employed a 25A7GT tube, which combined rectifier and pentode. The article noted that the set had a range of about a thousand miles on the broadcast band, but the parts list called for “a set” of plug-in coils. So there’s no reason why the set, with appropriate coils, couldn’t pull in shortwave signals.

The set uses the familiar “curtain burner” line cord to step down the filament voltage. Also, if you’re considering building such a set, there is an important safety reminder. Depending on which direction the line cord is plugged in, there’s a possibility that the chassis is hot. Even if you use a polarized cord to make sure the chassis is neutral, then the rectified line voltage is hooked directly to the headphones. So if you plan to recreate this particular set, please use extreme caution.

Rolite Trailers, 1969

This ad for Rolite trailers appeared fifty years ago this month in the April 1969 issue of Popular Mechanics. The Rolite was a solid-walled trailer that folded down. A 12-volt electric motor raised the roof and front and rear walls. The side walls were then raised manually, after which the roof was jogged down a couple of inches to lock everything in place.

Rolite was originally manufactured in Grantsburg, Wisconsin, in the mid-1960’s. By the time this ad appeared, they had become part of Larson Industries, 5000 Normandale Rd., Minneapolis. More information on the Rolite can be found at this Facebook group.

The ad was part of a 30-page supplement on camping, which also included the ads shown here:

The first is for a 5 horsepower motorbike kit (with optional ski), with a name familiar to regular readers, namely Heathkit! You can read more about the GT-18 at this link.

The second ad is for a class of product that has largely ceased to exist, namely, inexpensive, lightweight, no-frills tent trailers. They still exist, but most are marketed as motorcycle tent trailers. However, there’s no reason why one can’t be pulled behind a car. While I don’t think they are available in the U.S. any more, shown below is the 1980’s era Danish made Combi-Camp trailer we owned for a few years. Its empty weight was only a couple hundred pounds and could easily be towed by any car. Most importantly, it allowed you to camp but sleep off the ground, which is a huge luxury, but provided even by the simple trailer shown above.

For more information about the Appleby trailer shown in the ad, see this link or this Facebook page.