June 24, 2021

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Restoring a Vintage Tube Tester to its Former Glory

Restoring a Vintage Tube Tester to its Former Glory

Restoring a Vintage Tube Tester to its Former Glory

It can be difficult for modern eyes to make much sense of electronics from the 1960s or earlier. Between the point-to-point soldering, oddball components, and the familiar looking passives blown up to comical proportions like rejected props from “Honey, I Shrunk the Kids”, even experienced hardware hackers may find themselves struggling to understand what a circuit is doing. But that didn’t stop [Cat0Charmer] from taking the time to lovingly restore this Hickok Cardmatic KS-15874-L2 tube tester.

The good news was that the machine had nearly all of its original parts, down to the Hickok branded tubes in the power supply. Unfortunately it looks like a few heavy handed repairs were attempted over the years, with a nest of new wires and components intermixed with what [Cat0Charmer] actually wanted to keep. The before and after shots of individual sections of the machine are particularly enlightening, though again, don’t feel to bad if you still can’t make heads or tails of the cleaned up version.

Hiding new capacitors inside of the old ones.

As you’d expect for a machine of this age, many of the original components were way out of spec. Naturally the capacitors were shot, but even the carbon composition resistors were worthless after all these years; with some measuring 60% away from their original tolerances.

We particularly liked how [Cat0Charmer] hollowed out the old capacitors and installed the new modern ones inside of them, preserving the tester’s vintage look. This trick wasn’t always feasible, but where it was applied, it definitely looks better than seeing a modern capacitor adrift in a sea of 60’s hardware.

After undoing ham-fisted repairs, replacing the dud components, and installing some new old stock tubes, the tester sprung to life with renewed vigor. The previously inoperable internal neon lamps, used by the tester’s voltage regulation system, shone brightly thanks to all the ancillary repairs and changes that went on around them. With a DIY calibration cell built from the schematics in an old Navy manual, [Cat0Charmer] got the tester dialed in and ready for the next phase of its long and storied career.

We love seeing old hardware get restored. It not only keeps useful equipment out of the scrap heap, but because blending new and old technology invariably leads to the kind of innovative problem solving this community is built on.