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.

36 thoughts on “Restoring A Vintage Tube Tester To Its Former Glory

  1. “We particularly liked how [Cat0Charmer] hollowed out the old capacitors and installed the new modern ones inside of them”
    uhhh.. pcbs.. cancer… cant express how dangerous this is with old caps. With pcbs Dioxin formed as they degrade that is the actual hazard. and we all know from history how bad Dioxin is.

    1. The ones with PCB are big, and often/always in metal. “They say” that usually those are still good. And not all metal cased capacitors have PCB. I have some 1 or 2uF capacitirs in the basement, almost the first junk I ever collected, and I don’t worry.

    2. These are not too old for PCBs but more likely the cans are filled with tar. I was soaked to the skin with the stuff once when a guy knocked over a power pole transformer next to me with the top not fascenned but it didn’t affect me affect me affect me affect me affect me aff

    3. Wax capacitors and paper electrolytic capacitors do not contain PCBs. If they did, restoration projects would not be nearly as popular as they are now. Old metal caps in home equipment and old radios are safe.

    1. Sometime with ten or twenty years, some people have reported coming across a Radio Shack “guaranteed for life” tube. They took it to a store, and they actually replaced it. Except some other brand, and no more life time guarantee.

      The drugstore tube testers were vague, go/nogo, and probably favoured nogo, so more tubes would be sold.

      Fifty years ago, I don’t recall testers in drugstores, though at that age I didn’t go in kuch, except to buy chemicals. But tye electronic stores still had testers. I guess Radio Shack too.

      1. Dug stores, hardware stores, grocery stores. The had a light to show filament current (the most likely problem?) and a meter movement with a scale you compared to the viable range shown in the scroll for your tube. A bunch of switches you set based on the scroll numbers and a couple buttons you could press to take reradings – probably for the high voltage DC, the dials/rotary swtiches allowed testing sections, like in a pentode. I don’t recall anything as simple as a good/bad tester.

      2. I remember seeing tube testers in our local drug stores when I was a kid (early ’70s). The vast majority were simple emission testers, though they often tested for shorts and “gassy” (ie, air had leaked in) tubes. By tje time I was in high school (early ’80s) they had all disappeared.

  2. Tube rectifier circuits always my brain, and I have to reason my through understanding them. Then I repeat the process once again when I look at another circuit several months later. They just seem so bizarre.

    1. What, the old B+ comes off the filament trick? That was why those old tube set power transformers always had a dedicated winding for the rectifier — so that one could ‘float’ at several hundred volts.

  3. Neat. The easiest way to remove 10+ lbs from this kind of thing and reduce noise at the same time is replace the PSU with a switch mode module. Same for old PC’s like IMSAI8080 and the like. Massive transformers and caps to get 12V buss.

    1. That transformer has a tap for each heater voltage on the selector dial (15-20) voltages, not just 6 volts. Of course series tube designs were bad and hot chassis too. Strip it down to test 6 volt tubes only maybe 5 too if you want. 12AX7’s run on 6 volt.

      My boss was cleaning out his garage heated 2nd floor and found a tube tester little used before it’s 40years of storage. Bill of sale form the long gone radio store in town, it was from a competing music store also long gone. It cleaned up nicely and everything works no problems. Some testers used a rectified but not filtered supply and the “hum” was amplified and accounted for so I assume no ‘lytics in the supply.

    2. Depends on the application… switch-mode power supplies can spray a lot of RF noise around inside a cabinet, often causing interference in AM/shortwave radios. Also, it can be hard to find SMPC’s that will source 300+ volts often found in old tube equipment.

  4. This brings back the good old memories of the 50’s and 60’s. But soldering back than was a pain; point to point soldering. Lacing cables neatly. Also drawing out a schematic of the device was painful. I remember the schematics were blue prints in my days.

    1. We used to have to make our components out of discarded Lucas electric parts we collected on the streets of Hull.

      Then solder them with red hot pokers from open fires.

      We could only dream of having a valve to test!

  5. Fantastic work! Any Hickock is worth the effort to restore, but a Cardmatic – wow! I have had my military TV/7U for about 30 years now and it is still going strong. Probably will for another 30. Sometimes I lust after the features of an Amplitrex or µ-Tracer, but for reliability and ease of use the classics are hard to beat.

  6. What is the name of that point-to-point wiring between studs on a phenolic board? I’ve seen it being used still on modern tube guitar amplifiers. I seem to remember there was a name for the technique, but can’t recall.

      1. @joe b said: “That’s commonly referred to as ‘turret board’ construction.”

        Yes, that’s it. Also called ‘Terminal Board’ construction.[1] That Wikipedia page also led me to an entry on ‘Cordwood’ construction.[2] [joe b], thanks for the reply.

        * References:

        1. Turret board

        2. Printed circuit board – Cordwood construction

  7. The idea of hiding the new caps in the metal cans reminds me of a story of a fellow ham. He “fixed” a rectifier tube by taking it a part and installing a rectifier diode inside. Yeah, I know, not very elegant. But apparently, it worked good enough. A real crystal detector would have had a better characteristic curve, I believe. Anyway, I just thought I should mention that story. :)

  8. Cringing a little at the wholesale replacement of the original tubes. Tubes don’t normally age like electrolytics or carbon comps. Shotgunning them is traditionally a noob move, unless you’ve tested them already and confirmed them to have gone soft or open filament. I hope he kept them all for sake of testing them on his restored tester. Easy enough to swap back in and verify against some common tubes for a baseline ahead of time and then recheck after the swap back.

  9. Hello, congrats for this hack! I have the same model and every tube I test shows the meter going up to 64 and does not go pass that but the needle vibrates as it would go beyond that…any idea why this is happening? I recalibrated the machine but nothing changed. Thanks.

Leave a Reply

Please be kind and respectful to help make the comments section excellent. (Comment Policy)

This site uses Akismet to reduce spam. Learn how your comment data is processed.