A Tube Amplifier That’s Oven Ready

April 28, 2026 by Jenny List 19 Comments

The problem with tube based audio is that it has so often been hijacked by people for whom the bragging rights of having a tube amplifier outweigh the benefits, or the sheer fun of building the thing. [Bettina Neumryr] makes a speciality of building projects featured in old electronics magazines, and her latest, a tube amplifier from 1955, is a fantastic antidote to the gold-plated silliness of audiophile tube amplifiers.

Design wise it’s relatively straightforward, with a preamplifier before a two-tube transformerless splitter circuit driving a push-pull output. She dives into the circuit a little, noting its feedback circuit to the cathode of the first splitter tube. There’s an accompanying power supply, a classic tube rectifier design that incorporates a hefty low-pass filter with a giant choke.

We particularly like her choice of chassis — while it’s possible to pay silly money for a tube chassis in 2026 she’s taken a much more down to earth approach with a pair of baking trays. We’re being honest here, they look surprisingly good. Component choices are limited by what’s available so most parts come from the junk box including the output transformer which causes her issues later. There’s a lot of mumbo-jumbo about tube amplifier layout, and she wisely sidesteps some of it.

The result after a few mishaps and a bit of unintended oscillation, is an amp which shows promise, but has distortion due to that transformer. We think she’ll have no problems sourcing a better one, which should bring that distortion figure into the acceptable range. You can watch the whole video below the break, and if that’s got you hooked, you can see one of our own youthful follies.

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Audio-Forward Case Mod Of Classic 90s Portable TV

April 24, 2026 by Bryan Cockfield 8 Comments

The humble cathode ray tube (CRT) was once the technology behind almost all of our televisions and computer displays. Its replacements, from LCD screens to OLED and others, are generally cheaper to make and better to look at. Old televisions were comparatively large as well, but their size can be an advantage for people like [ManicMods] aka [Jeff]. His latest build ditches the CRT from an old Bently portable TV and uses the huge space available in the case for a hi-fi audio system and some other parts that turn it into an impressive portable home theater system.

After removing most of the internals of the TV, the first part to go in is the stereo and subwoofer combo as it takes up the most amount of space. The subwoofer section points downward and the two stereo speakers are mounted to the sides. To free up the most space inside, the new display is mounted forward of the original bezel, with a new 3D printed one helping to hold it in place. Behind it goes a Raspberry Pi, loaded with the moOde audio player, a high quality DAC for audio output, and a 1 TB SSD with [Jeff]’s uncompressed audio library. Most of the ports are extended out to the case including the SD card slot so other operating systems can be loaded on the Pi, and there are a ton of options for hooking up external speakers and displays as well, making it an extremely modular and expandable portable media center.

Also added to the finished product are a few small game controllers, since the Pi is perfectly capable of playing retro games, as well as a small wireless keyboard and trackpad combo. Although the CRT’s demise will be felt harder by some than by others, the original look of the case is preserved somewhat by keeping the original tuning display and locations of the original control buttons and knobs. If preserving the CRTs are of upmost importance, though, this build used a pair of them in a VR headset.

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Heathkit Tuner Saved From Junk Pile

April 4, 2026 by Al Williams 4 Comments

We miss the old Heathkit. You could build equipment that rivaled or even surpassed commercial devices. The cost was usually reasonable and, even if you could get by with less, the satisfaction of using gear you built yourself was worth a lot. Not to mention the knowledge you’d gain and your confidence in troubleshooting should the need arise. So we were jealous of [RCD66] when he found a Heathkit AJ-43C stereo tuner in the recycle bin.

As you can see in the video below, it needed a lot of love to get back to its former self. The device dates from around 1965, when the kit cost $130. In 1965, that was a lot of money. Back then, that would have bought you about four ounces of gold and would have been a great down payment on a $1,500 VW bug.

Things were a bit of a mess, so he removed all the parts and replaced most of them. Unsurprisingly, the electrolytic capacitors all tested bad. The transistors were all germanium, but if they tested good, his plan was to reuse them. There were several PCBs inside, and he made some changes, such as replacing the zener diode power supply with something more modern.

How did it sound? Watch the video and see for yourself. We usually like troubleshooting specific problems on gear like this, but in this case, it was probably smart to just do a total rework.

Heathkit had quite an origin story. This isn’t the first time we’ve seen someone strip and rebuild a Heathkit.

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Mercury Audio Cables, So Nobody Else Has To Do It

April 1, 2026 by Jenny List 67 Comments

We’ve seen our fair share of audiophile tomfoolery here at Hackaday, and we’ve even poked fun at a few of them over the years. Perhaps one of the most outrageously over the top that we’ve so far seen comes from [Pierogi Engineering] who, we’ll grant you not in a spirit of audiophile expectation, has made a set of speaker interconnects using liquid mercury.

In terms of construction they’re transparent tubes filled with mercury and capped off with 4 mm plugs as you might expect. We hear them compared with copper cables and from where we’re sitting we can’t tell any difference, but as we’ve said in the past, the only metrics that matter in this field come from an audio analyzer.

But that’s not what we take away from the video below the break. Being honest for a minute, there was a discussion among Hackaday editors as to whether or not we should feature this story. He’s handling significant quantities of mercury, and it’s probably not over reacting to express concerns about his procedures. We wouldn’t handle mercury like that, and we’d suggest that unless you want to turn your home into a Superfund site, you shouldn’t either. But now someone has, so at least there’s no need for anyone else to answer the question as to whether mercury makes a good interconnect.

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Fixing An Onkyo Receiver With Multiple Faults

March 7, 2026 by Maya Posch 12 Comments

Modern-day receivers are miracles of digital audio and video processing, but compared to their more analog brethren, they can come with a host of new and fascinating faults. The Onkyo TX-SA806 and SR806 receivers were released back in 2008, with [Tony359] recently getting the latter variant in for repair. Described as having weird digital distortion on the audio outputs, this particular issue got fixed by recapping the PCB with all the digital processing in the first video on this receiver, but this left the second issue unaddressed of a persistent hum, which is the topic of the second video on this repair.

Capacitor C5662 in the Onkyo TX-SR608 receiver with a slight bulge. (Credit: Tony359, YouTube) — Capacitor C5662 in the Onkyo TX-SR608 receiver with a slight bulge.

With the easy fix of recapping of the digital board already tried, next was a deep-dive into the receiver’s schematics to figure out where this low-frequency hum was coming from. With it sounding very much like mains frequency hum bleeding through, this was the starting point. Presumably somewhere on the power rails the normal filtering had broken down, so all rails had to be identified and checked for this interference.

With ripple on the 10V and 12V rails as well as the others seemingly in order, it wasn’t clear where the 100 Hz hum was coming from, but people on the BadCaps forum offered some help. After some back and forth it was deduced that the problem was the +15 VA rail, with heavy ripple on it due to a dead capacitor on the +22 V rail that comes straight from a transformer.

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Philco Bet The Farm On The Predicta… And Lost

February 27, 2026 by Al Williams 31 Comments

Philco was a common household brand for many years. The company started in 1892, making street lights. Then they pivoted to batteries. This was big business when early radios were all battery-operated. But in the 1920s, line-powered radios threatened to shrink their customer base, so they pivoted again. This time, they started making radios. So what happened? [The Last Shift] has the story, and you can see the video below.

Philco used advanced manufacturing techniques to make radios more affordable. By 1930, they were the number one radio maker in the world. After World War II, they moved into everything electric: mostly appliances, but also the new king of the electronics market, the television.

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HD On A VHS Tape? How Did They Do It?

February 20, 2026 by Jenny List 10 Comments

There was a period from the 1970s to the mid-2000s or so when a fixture underneath the family TV set was a VHS videocassette recorder. These were a masterpiece of cramming a color video signal into the restricted bandwidth of an affordable 1970s helical-scan tape deck, which was achieved by clever use of frequency shifting and FM carrier modulation. Very few of us will have had the ultimate iteration of the VHS format though, W-VHS, which managed the same trick but with HD video. But how? [Superchromat] is here with the answer.

W-VHS used a frequency modulated carrier, but instead of splitting luminance and chrominance in the frequency domain like its VHS ancestor, it did so in the time domain in the same way as some 1980s satellite TV standards did. Each line first contained the color information, then the brightness. Thus it sacrificed some color resolution and a little horizontal image resolution, but kept a much higher vertical image resolution. In the video below the break we go into significant detail about the compromises required to pull this off, and if you watch it through you’ll learn something about magnetic tape recording as well as FM.

The W-VHS standard is largely forgotten now as a last hurrah for the format, but it’s still in the sights of the VHS Decode project. The work in this video is helping them retrieve the highest quality images from these tapes, by capturing the raw RF from the heads and using DSP techniques to decode them.

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