Humble Television Tubes Make An FM Regenerative Radio

November 4, 2024 by Jenny List 10 Comments

The regenerative radio is long-ago superseded in commercial receivers, but it remains a common project for electronics or radio enthusiasts seeking to make a simple receiver. It’s most often seen for AM band receivers or perhaps shortwave ham band ones, but it’s a circuit which also works at much higher frequencies. [Perian Marcel] has done just this, with a regenerative receiver for the FM broadcast band.

The principle of a regenerative receiver is that it takes a tuned radio frequency receiver with a wide bandwidth and poor performance, and applies feedback to the point at which the circuit is almost but not quite oscillating. This has the effect of hugely increasing the “Q”, or quality factor of the receiver, giving it much more sensitivity and a narrow bandwidth. They’re tricky to tune but they can give reasonable performance, and they will happily slope-demodulate an FM transmission.

This one uses two tubes from consumer grade TV receivers, the “P” at the start of the part number being the giveaway for a 300mA series heater chain. The RF triode-pentode isn’t a radio part at all, instead it’s a mundane TV field oscillator part pushed into service at higher frequencies, while the other triode-pentode serves as an audio amplifier. The original circuit from which this one is adapted is available online, All in all it’s a neat project, and a reminder that exotic parts aren’t always necessary at higher frequencies. The video is below the break.

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Braun TS2 Radio Turns 68, Gets Makeover

October 9, 2024 by Al Williams 7 Comments

The Braun TS2 radio was a state-of-the art tube set in 1956. Today it still looks great, but unsurprisingly, the one that [Manuel Caldeier] has needed a little tender loving care. The table radio had a distinct style for its day and push-buttons. However, the dial glass and the speaker grill needed replacement. Even more interesting, the radio has a troublesome selenium rectifier, giving him the perfect chance to try out his new selenium rectifier solid-state replacement.

The radio is as good-looking inside as it is outside. You can tell that this isn’t his first restoration, as he has several tricks to test things at different stages of the project.

While the radio looked good, it smelled of smoke, which required a big effort to clean. The dial glass was intact enough for him to duplicate it in a graphic program and print it on a transparent adhesive sticker. With a deep breath, he removed the original markings from the glass so he could add the sticker to it. That didn’t work because the label needed cutouts. So now he is waiting for a piece of acrylic that will have the art UV printed on it.

We want to see the next part as we imagine the radio sounds as good as it looks when it is working. If you want to know more about the rectifier replacement, we covered that earlier. Even years later, Braun would have a clean aesthetic.

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A 1940s Car Radio Receives Some Love

June 13, 2024 by Jenny List 9 Comments

The entertainment systems in modern vehicles is akin to a small in-dash computer, and handles all manner of digital content. It probably also incorporates a radio, but increasingly that’s treated as something of an afterthought. There was a time though when any radio in a car was a big deal, and if you own a car from that era it’s possible that you’ve had to coax an aged radio into life. [The Radio Mechanic] is working on a radio from a 1946 Packard, which provides a feast for anyone with a penchant for 1940s electronics.

The unit, manufactured by Philco, is an all-in-one, with a bulky speaker in the chassis alongside the tubes and other components. It would have sat behind the dash in the original car, so some external cosmetic damage is not critical. Less easy to pass off is the cone rubbing on the magnet, probably due to water damage over the last eight decades. Particularly interesting are the controls, as we’re rather enamored with the multicolored filter attached to the tone control. A laser cutter makes short work of recreating the original felt gasket here.

The video below is the first of a series on this radio, so we don’t see it working. Ahead will be a lot more cleaning up and testing of components, and we’d expect a lot of those paper capacitors to need replacement. We can almost smell that warm phenolic smell.

If tube radio work is your thing, we’ve been there before.

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Blaupunkt Tube Radio Is The Sultan Of Radios

October 8, 2023 by Al Williams 16 Comments

According to [M Caldeira], the Blaupunkt Sultan 24300 was one of the last tube radios made in the 1960s. He’s got one but it needed some tender loving care, and you can see how he approaches a restoration like this in the video below.

The radio was actually in better shape physically than most of the old radios we see. It wasn’t perfect, but it looked good on the outside. Electrically, though, it did need some work, and the dial had problems, too. The first obstacle was identifying exactly the model of the radio since there were a number of Sultan radios produced.

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All American Five Lives Again

August 1, 2023 by Al Williams 18 Comments

If you haven’t heard of an “all-American five,” then you probably don’t dig through bins for old radios. The AA5 is a common design for old AM radios that use five tubes: a rectifier, an oscillator/mixer, an IF amplifier, a detector, and a single tube for driving the speaker. [Mikrowave1] took an old specimen of such a radio from the mid-1950s and wanted to restore it. You can see how it went in the video below.

One feature of the design is that the set had a “hot chassis,” which means you really want to use an isolation transformer before you work on it. We were taught to touch a chassis with the back of our hand first because of radios like this. If it is “hot,” the muscle contraction would throw your arm away from the radio instead of forcing you to grip it uncontrollably.

The GE radio had many quality design touches you don’t always see in a radio like this. The mix of brands indicates that the radio has had tubes replaced in the past. It also had a clearly replaced electrolytic capacitor. Surprisingly, all the tubes were good, although the power output tube was marginal. However, a light bulb was bad and required a little surgery to allow for a slightly different replacement.

Some capacitors were neatly replaced, also. A lot of cleaning and testing later — along with a dropped tool — the radio was ready to play again. Fixing radios from this era is a great hobby. You can get to everything and you don’t really need anything fancy, although a tube tester is helpful. The classic method of troubleshooting is to either find audio on the volume control or not and then work your way backward or forward using a signal tracer or — since they are so readily available now — a scope. Alternatively, you could inject a signal at the volume control and work your way through the circuit until you can or can’t hear the injected signal.

Not the first tube radio we’ve watched being restored, of course. Need a tube tester?

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1920’s Claratone Radio Runs Windows 10

April 10, 2018 by Tom Nardi 31 Comments

In the past we’ve mentioned how there are different schools of thought in terms of how to bring a vintage piece of hardware into the 21st century. You can go down the preservationist’s route, carefully grafting the original components with more modern ones, or you can take the nuclear option and blow all that dusty old gear out of the water. [Derek Traxler] clearly decided to go with the latter option on his recent conversion of 1920’s era Claratone tube radio to an Internet radio and podcast player. Not only is there little left of the original device beyond its knobs and wooden case, but he’s even managed to cram a Windows 10 computer into the base for good measure.

The core of the radio is a LattePanda, an extremely powerful Intel single board computer. It’s running Windows, and loads up a list of Internet radio streams and podcasts to play from a USB thumb drive that’s built into an old vacuum tube. The LattePanda uses its built-in Arduino to interface with the radio’s original front panel knobs, which now are used to switch between streams. A particularly neat effect is the static and cross-talk that’s artificially added when switching “stations”, making it sound like you’re really dialing in a station rather than just selecting between digital files.

On the audio side, the LattePanda is connected to a SX400 amplifier, which in turn drives the external speakers. While [Derek] mentions it isn’t quite perfected, a MSGEQ7 graphic equalizer chip is used to control LEDs mounted inside the original radio’s vacuum tubes. In the video after the break, you can see the tubes flashing madly along with the music, giving an interactive effect to the final product. Unfortunately it seems you can only see the tubes when the radio has its “hood” up, though.

If this egregious lack of historical preservation has brought a tear to your eye, never fear. We’ve covered some proper restoration work on vintage audio gear which may level you out.

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This IS Your Grandfather’s Radio

February 14, 2018 by Al Williams 9 Comments

Tube radios have a certain charm. Waiting for them to warm up, that glow of the filaments in a dark room. Tubes ruled radio for many decades. [Uniservo] posted a video about the history and technology behind the 1920’s era Clapp-Eastham C-3 radio. This is a three-tube regenerative receiver and was advanced for its day.

If you are worried he won’t open it up, don’t despair. Around the ten minute mark, your patience will be rewarded. Inside are three big tubes full of getter and bus bars instead of wires. Add to that the furniture-quality case, and this is a grand old radio.

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