How Simple Can A Superhet Be

October 30, 2025 by Jenny List 20 Comments

If you cultivate an interest in building radios it’s likely that you’ll at some point make a simple receiver. Perhaps a regenerative receiver, or maybe a direct conversion design, it’ll take a couple of transistors or maybe some simple building-block analogue ICs. More complex designs for analogue radios require far more devices; if you’re embarking on a superhetrodyne receiver in which an oscillator and mixer are used to generate an intermediate frequency then you know it’ll be a hefty project. [VK3YE] is here to explode that assumption, with a working AM broadcast band superhet that uses only two transistors.

The circuit diagram of the radio — It doesn’t get much simpler than this.

A modern portable radio will almost certainly use an all-in-one SDR-based chip, but in the golden age of the transistor radio the first stage of the receiver would be a single transistor that was simultaneously RF amplifier, oscillator, and mixer. The circuit in the video below does this , with a ferrite rod, the familiar red-cored oscillator coil, and a yellow-cored IF transformer filtering out the 455 kHz mixer product between oscillator and signal.

There would normally follow at least one more transistor amplifying the 455 kHz signal, but instead the next device is both a detector and an audio amplifier. Back in the day that would have been a germanium point contact diode, but now the transistor has a pair of 1N4148s in its biasing. We’re guessing this applies a DC bias to counteract the relatively high forward voltage of a silicon diode, but we could be wrong.

We like this radio for its unexpected simplicity and clever design, but also because he’s built it spiderweb-style. We never expected to see a superhet this simple, and even if you have no desire to build a radio we hope you’ll appreciate the ingenuity of using simple transistors to the max.

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When Transistor Count Mattered

December 1, 2024 by Jenny List 29 Comments

Many Hackaday readers have an interest in retro technology, but we are not the only group who scour the flea markets. Alongside us are the collectors, whose interest is as much cultural as it is technological, and who seek to preserve and amass as many interesting specimens as they can. From this world comes [colectornet], with a video that crosses the bridge between our two communities, examining the so-called transistor wars of the late 1950s and through the ’60s. Just as digital camera makers would with megapixels four or five decades later, makers of transistor radios would cram as many transistors as they could into their products in a game of one-upmanship.

A simple AM transistor radio can be made with surprisingly few components, but for a circuit with a reasonable performance they suggest six transistors to be the optimal number. If we think about it we come up with five and a diode, that’s one for the self-oscillating mixer, one for IF, an audio preamplifier, and two for the audio power amplifier, but it’s possible we’re not factoring in the relatively low gain of a 1950s transistor and they’d need that extra part. In the cut-throat world of late ’50s budget consumer electronics though, any marketing ploy was worth a go. As the price of transistors tumbled but their novelty remained undimmed, manufacturers started creating radios with superfluous extra transistors, even sometimes going as far as to fit transistors which served no purpose. Our curious minds wonder if they bought super-cheap out-of-spec parts to fill those footprints.

The video charts the transistor wars in detail, showing us a feast of tiny radios, and culminating in models which claim a barely credible sixteen transistors. In a time when far more capable radios use a fraction of the board space, the video below the break makes for a fascinating watch.

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How Sony Mastered The Transistor

September 4, 2024 by Al Williams 35 Comments

When you think of Sony, you probably think of a technology company that’s been around forever. However, as [Asianometry] points out, it really formed in the tough years after World War II. The two people behind the company’s formation were an interesting pair. One of them was a visionary engineer and one was a consummate businessman.

While it is hard to imagine today, securing a license to produce transistors was difficult in the early days. What’s worse is, even with the license, it was not feasible to use the crude devices in a radio.

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Transistor Radio Repair, More Complex Than It Seems

September 7, 2023 by Jenny List 48 Comments

The humble transistor radio is one of those consumer devices that stubbornly refuses to go away, but it’s fair to say that it’s not the mover and shaker in the world of electronics it might once have been. Thus it’s also not a staple of the repair bench anymore, where fixing a pocket radio might have been all in a day’s work decades ago now they’re a rare sight. [David Tipton] has a Philips radio from we’re guessing the later half of the 1960s which didn’t work, and we’re along for the ride as he takes us through its repair.

It’s an extremely conventional design of the era, with a self-oscillating mixer, 455 kHz IF amplifier, and class AB audio amplifier. The devices are a little archaic by today’s standards, with comically low-gain germanium transistors and passives from the Ark. Injecting a signal reveals that the various stages all work, but that mixer isn’t oscillating. A lot of fault-finding ensues, and perhaps with a little bit of embarrassment, he eventually discovers a blob of solder shorting a collector resistor to ground. All isn’t over though, for the volume pot is also kaput. Who knew that the track from a modern component could be transplanted into one from the 1960s?

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A Vintage Transistor Radio Gets A Repair

July 24, 2023 by Jenny List 19 Comments

Here in 2023 the field of electronics covers a breathtaking variety of devices and applications, but if we were to go back in time far enough we’d enter an age in which computers were few and far between, and any automated control systems would have been electromechanical at best. Back in the 1950s the semiconductor industry was in relative infancy, and at the consumer end electronics were largely synonymous with radio. [Shango066] brings us a transistor radio from that era, a Jewel TR1 from about 1958, that despite its four-transistor simplicity to our eyes would have been a rare and expensive device when new.

As you’d expect, a transistor radio heading toward its 70th birthday requires a little care to return to its former glory, and while this one is very quiet it does at least work after a fashion. The video below the break is a long one that you might wish to watch at double speed, but it takes us through the now-rare skill of fault-finding and aligning an AM radio receiver. First up are a set of very tired electrolytic capacitors whose replacement restores the volume, and then it’s clear from the lack of stations that the set has a problem at the RF end. We’re treated to the full process of aligning a superhet receiver through the relatively forgiving low-frequency medium of a medium-wave radio. Along the way, he damages one of the IF transformers and has to replace it with a modern equivalent, which we would have concealed under the can from the original.

The video may be long, but it’s worth a look for the vintage parts if not for the quality of radio stations on the air today in California. For many readers, AM broadcast is becoming a thing of the past, so we’re not sure we’ll see this very often.

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AJAX COMMAND Radio Is An Oldie But Goodie

July 3, 2022 by Al Williams 32 Comments

If you are a certain age, it is hard to wrap your head around the fact that an old radio might have transistors — the old ones all had tubes, right? But a radio from the 1960s or 1970s is reaching the 60+ year mark and people are restoring old transistor sets. [Adam] picked up his first old radio, a 1970s vintage Ajax Command S-74.

He was fortunate. The only repair needed was to replace a corroded battery holder and clean up the mess from the batteries. You can hear the radio doing its thing in the video below.

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Books You Should Read: Making A Transistor Radio

February 3, 2017 by Jenny List 33 Comments

When a Hackaday article proclaims that its subject is a book you should read, you might imagine that we would be talking of a seminal text known only by its authors’ names. Horowitz and Hill, perhaps, or maybe Kernigan and Ritchie. The kind of book from which you learn your craft, and to which you continuously return to as a work of reference. Those books that you don’t sell on at the end of your university career.

Ladybird books covered a huge range of topics.

So you might find it a little unexpected then that our subject here is a children’s book. Making A Transistor Radio, by [George Dobbs, G3RJV] is one of the huge series of books published in the UK under the Ladybird imprint that were a staple of British childhoods for a large part of the twentieth century. These slim volumes in a distinctive 7″ by 4.5″ (180 x 115 mm) hard cover format were published on a huge range of subjects, and contained well written and informative text paired with illustrations that often came from the foremost artists of the day. This one was published at the start of the 1970s when Ladybird books were in their heyday, and has the simple objective of taking the reader through the construction of a simple three transistor radio. It’s a book you must read not because it is a seminal work in the vein of Horrowitz and Hill, but because it is the book that will have provided the first introduction to electronics for many people whose path took them from this humble start into taking the subject up as a career. Including me as it happens, I received my copy in about 1979, and never looked back. Continue reading “Books You Should Read: Making A Transistor Radio” →