A Stereo Tube Amp For Less Than $5

July 30, 2018 by Ben James 21 Comments

Many of us have aspirations of owning a tube amp. Regardless of the debate on whether or not tube audio is nicer to listen to, or even if you can hear the difference at all, they’re gorgeous to look at. However, the price of buying one to find out if it floats your boat is often too high to justify a purchase.

[The Post Apocalyptic Inventor] has built a stereo tube amplifier in the style of the Fallout video games. The idea came when he realised that the TK 125 tape recorder manufactured by Grundig was still using tube audio in the late 60s. What’s more, they frequently sell on eBay for 1-10€ in Germany. [TPAI] was able to salvage the main power amplifier from one of these models, and restore it so that it could be re-purposed and see use once more.

The teardown of the original cassette recorder yields some interesting parts. Firstly, an integrated motor transformer — an induction motor whose stator acts as the magnetic core of the transformer responsible for the tube electronics. There’s also an integrated capacitor which contains three separate electrolytics. The video after the break is well worth a watch (we always find [TPAI]’s videos entertaining).

A new chassis is created out of a steel base plate and aluminium angle, and some neat frames for the motor transformers are made from scrap copper wire bent and soldered together. It looks great, though there’s always the option to use a cake tin instead.

If you’re interested in the design of tube amps, we’ve covered heaps of cool builds: from this low-voltage design to this tiny guitar amp, or even ones using tubes which are flat.

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Amiga Repairs Put One Tough Little Machine Back in Service

July 30, 2018 by Dan Maloney 8 Comments

Returning a piece of retro hardware to factory condition is generally a labor of love for the restorationist. A repair, on the other hand, is more about getting a piece of equipment back into service. But the line between repair and restoration is sometimes a fine one, with the goals of one bleeding over into the other, like in this effort to save an otherwise like-new Amiga 2000 with a leaky backup battery.

Having previously effected emergency repairs to staunch the flow of electrolyte from the old batteries and prevent further damage, [Retromat] entered the restoration phase of the project. The creeping ooze claimed several caps and the CPU socket as it spread across the PCB, but the main damage was to the solder resist film itself. In the video below you can clearly see flaky, bubbly areas in the mask where the schmoo did its damage.

Using a fiberglass eraser, some isopropyl alcohol, and far more patience than we have, [Retromat] was able to remove the damaged resist to reveal the true extent of the damage below. Thankfully, most of the traces were still intact; only a pair of lines under the CPU socket peeled off as he was removing it. After replacing them with fine pieces of wire, replacing the corroded caps and socket, and adding a coin-cell battery holder to replace the old battery, the exposed traces were coated with a varnish to protect them and the machine was almost as good as new.

Amigas were great machines in their day and launched more than one business. They’ve proved their staying power too, some even in mission-critical roles.

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Incredible Atari 800XL Case Restoration

July 15, 2018 by Tom Nardi 26 Comments

If you’ve been hanging around Hackaday for a while, you know that a large portion of the stuff we publish goes above and beyond what most people would consider a reasonable level of time and effort. One could argue that’s sort of the point: the easy way out is rarely the most exciting and interesting route you can take. We, and by extension our readers, are drawn to the projects that someone has really put their heart and soul into. If the person who created the thing wasn’t passionate about it, why should we be?

That being said, on occasion, even we are left in awe about the lengths some people will go to. A perfect example of this is the absolutely insane amount of time and effort [Drygol] has put into restoring an Atari 800XL that looked like it was run over by a truck. Through trial, error, and a bunch of polyester resin, he’s recreated whole sections of the Atari’s case that were missing.

To start the process, [Drygol] used metal rods to bridge the areas where the plastic was completely gone. By heating the rods with a torch and pushing them into the Atari’s case, he was able to create a firm base to work from. Additional rods were then soldered to these and bent, recreating the shape of the original case. With the “skeleton” of the repair in palce, the next step was filling it in.

[Drygol] borrowed an intact Atari 800XL case from a friend, and used that to create a mold of the missing sections from his own case. Most of his rear panel was missing, so it took some experimentation to create such a large mold. In the end he used silicone and a custom built tray that the case could sit in vertically, but he does mention that he never quite solved the problem of degassing the silicone. The mold still worked, but bubbles caused imperfections which needed to be filled in manually during the finishing process.

Using his silicone mold and the same tray, he was then able to pour polyester resin over the wire frame. This got him most of the way to rebuilding the case, but there was still plenty of filler and sanding required before the surface finish started to look half-way decent. When he got towards the very end of the finishing process, he used a mold he created of the case surface texture to roughen up the smooth areas left over from the filling process. Add a bit of custom spray paint, and the end result looks absolutely phenomenal considering the condition it was in originally.

We were already impressed by the work he put in during the first stages of the restoration, but this case repair is really on a whole new level. Between this and the incredible instructional videos [Eric Strebel] has been putting out, we’re really gaining a whole new respect for the power of polyester.

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Refurbishing A DEC 340 Monitor

June 19, 2018 by Al Williams 16 Comments

Back in the “good old days” movie theaters ran serials. Every week you’d pay some pocket change and see what happened to Buck Rogers, Superman, or Tex Granger that week. Each episode would, of course, end in a cliffhanger. [Keith Hayes] has started his own serial about restoring a DEC 340 monitor found in a scrap yard in Australia. The 340 — not a VT340 — looks like it could appear in one of those serials, with its huge cabinets and round radar-like display. [Keith] describes the restoration as “his big project of the year” and we are anxious to see how the cliffhangers resolve.

He’s been lucky, and he’s been unlucky. The lucky part is that he has the cabinet with the CRT and the deflection yoke. Those would be very difficult to replace. The unlucky part is that one entire cabinet of electronics is missing.

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Restoring an Atari 800 XL that’s Beyond Restoring

June 9, 2018 by Tom Nardi 24 Comments

Sometimes the best way to get a hacker to do something is to tell them that they shouldn’t, or even better can’t, do it. Nothing inspires the inquisitive mind quite like the idea that they are heading down the road less traveled, if for nothing else to say that they did it. A thrown gauntlet and caffeine is often all that stands between the possible and the impossible.

So when [Drygol] heard a friend comment he had an old Atari 800 XL that was such poor shape it couldn’t be repaired, he took on the challenge of restoring the machine sight unseen. Luckily for us, his pride kept him from backing down when he saw the twisted and dirty mess of a computer in person. He’s started documenting the process on his blog, and while this is only the first phase of the restoration, the work he’s done already is impressive enough that we think you’ll want to follow him along on his quest.

There’s no word on what happened to this miserable looking Atari, but we wouldn’t be surprised if it was run over by a truck. The board was cracked and twisted, with some components missing entirely. The first step in this impossible restoration was straightening the PCB, which [Drygol] did by clamping it to some aluminum bar stock and heating the whole board up to 40C (104F) for a few days. Once the got most of the bend out, he used a small drill bit to put holes in the PCB laminate and inject epoxy to add some strength. It’s an interesting technique, and the results seem to speak for themselves.

Once the board was straight, he went through replacing blown passive components and broken chip sockets. All the ICs were pulled and treated to an isopropyl alcohol and acetone bath in an ultrasonic cleaner to get them looking like new again. The CPU was cooked and needed to get swapped out, but otherwise it was smooth sailing, and before long he had the machine booted up. While most would have been satisfied to just get this far, [Drygol] considers this to be the easy part.

He next straightened out the metal shielding with a mallet, sanded it down, and sprayed it with a new zinc coating. The plastic around the keyboard and the metal trim pieces were also removed, cleaned, and refinished where necessary. Rather than going for perfection, [Drygol] intentionally left some issues so the machine didn’t look 100% pristine. It’s supposed to be a functional computer, not a museum piece behind glass.

We’ll have to wait until the next entry in this series to see how he repairs the absolutely devastated case. Any rational person would just use a case from a donor machine, but we’ve got a feeling [Drygol] might have something a little more impressive in mind.

In the meantime we’ve got plenty of incredible restorations to keep you occupied, from this sunken VIC-20 to a Pi-packing Osborne.

Bringing a VIC-20 Back from an Oily Grave

May 25, 2018 by Dan Maloney 17 Comments

No matter which platform you’re into, retrocomputing is usually a labor of love. The obsolete, the unpopular, the downright weird – old computers of every stripe are found, restored to something like their former glory, and given a new lease on life. It’s heartwarming, in a way. But when a computer has obviously been abused, it takes a little extra effort, of a lot in the case of this oil-submerged VIC-20 restoration.

In the two-part video below, [The 8-Bit Guy] goes through the gory details of bringing this classic Commodore back from the grave. The first video shows the cosmetic rebuild, which given the filthy state of the machine was no mean feat. Cracked open, the guts were found to be filled with an oily residue; [The 8-Bit Guy] chalks that up to a past life in some kind of industrial setting, but we see it more as flood damage. Whatever the sad circumstances on the machine’s demise, the case required a workout to clean up, and it came out remarkably fresh looking. The guts needed quite a bit of cleaning too, mainly with brake cleaner to cut through the gunk.

Part two focuses on getting the machine running again, and here [The 8-Bit Guy] had his work cut out as well. With a logic probe, signal injector, and some good old-fashioned chip swapping, he was able to eliminate most of the potential problems before settling in on some RAM chips as culprits for the video problems he saw at power-up. It all worked out in the end, and the machine looks and acts like new. We’re impressed.

Maybe we shouldn’t question [The 8-Bit Guy]’s call on the VIC-20 being from an industrial setting, though. After all, the “little Amiga that could” ran a school’s HVAC system for over 30 years.

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Restoring A 1930s Oscilloscope – Without Supplying Power

May 22, 2018 by Ben James 36 Comments

We’ve all done it: after happening across a vintage piece of equipment and bounding to the test bench, eager to see if it works, it gets plugged in, the power switch flipped, but… nothing. [Mr Carlson] explains why this is such a bad idea, and accompanies it with more key knowledge for a successful restoration – this time revitalising a tiny oscilloscope from the 1930s.

Resisting the temptation to immediately power on old equipment is often essential to any hope of seeing it work again. [Mr Carlson] explains why you should ensure any degraded components are fixed or replaced before flipping the switch, knowing that a shorted/leaking capacitor is more than likely to damage other components if power is applied.

The oscilloscope he is restoring is a beautiful find. Originally used by radio operators to monitor the audio they were transmitting, it features a one inch CRT and tube rectification, in a tight form factor.

[Mr Carlson] uses his capacitor leakage tester to determine if the main filter capacitor needs replacing – it does, no surprises there – as well as confirming the presence of capacitors potted into the power transformer itself. These have the potential to not only derail the restoration, but also cause a safety hazard through leakage to the chassis.

After replacing and rewiring everything that’s relevant, the scope is hooked up to an isolation transformer, and it works first time – showing the value of a full investigation before power-up. [Mr Carlson] quips, “It really doesn’t have a choice; when it’s on this bench, it’s going to work again”, a quote which will no doubt resonate with Hackaday readers.

[Mr Carlson] promises to integrate the scope into a new piece of test equipment in the near future, but in the meantime you can read about his soldering station VFD mod, or his walk-in AM radio transmitter.

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