Restoring A 1930s Oscilloscope – Without Supplying Power

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.

36 thoughts on “Restoring A 1930s Oscilloscope – Without Supplying Power

    1. Youtube really should add the ability to skip around in a video. If only there were some interface, maybe a slider bar across the bottom of the screen? Just spit balling here, i’m sure there’s a better idea.

          1. okay… well then you perhaps are not aware of the “” keys that allows you to move the video frame by frame. Useful when you want to see a specific part of the video or when the video goes to fast. A function that only works when the video is paused.

          2. oka… the “greater then” and “less then” keys of the keyboard are characters that can’t be used in the comments. Hm… this made my comment look very silly.

    2. Not always relevant (and unfortunately not in this case, either), but taking a quick peek at the top comments can often yield some time codes for interesting bits. If you’re only interested in seeing it operating, jump to 39:50. The early parts have some good shots of the guts, and there are some shots of the schematics in the last half as well.

    3. Also (sorry for spam), you can hover over the transport bar to receive a thumbnail at that timecode, at least in desktop browsers… very useful for hunting down the bits you want.

    1. If it is possible to de-pot the transformer and remove the faulty capacitor(s) then that would keep the little ‘scope as authentic as possible. External timebase and y amps would also keep the ‘scope close to its original form. If you change it too much you might as well scrap it entirely and buy a Rigol.

  1. Interesting. I happen to have a Tektronics that looks like it’s from the 1950s that I have not attempted to power up before, and had thought about restoring. Even without watching the video, this post gives me a lot to watch out for.

    1. Slightly off-topic,
      I have a couple of military LCR bridges at home, and haven’t found any manuals for them.
      I found an online manual for a civilian one made by a different company, but the terminology describing the controls is quite different.

      1. They can show up in the weirdest places. I picked up a Tektronix RM16 at a rummage sale put on by a local church. It seems to have been donated by a church member rather than something actively kept at the church. A lot of second-hand sales can turn up interesting projects – as long as you’re not too picky about what sort of project.

  2. Mr. Carlson always acts so humble despite his obvious skill and experience. But really, that statement about stuff on his bench is not bragging, he is just that good. Amazes me every time (if I can spare an hour or so to watch the video).

  3. By the time the project gets repeated here, most of these folks have already watched it and it’s like watching repeats on the Hackaday +1 week channel. We all seem to love Carlson’s work even if it does tend to last out quite a while. I wont watch it again with in the week its too long even if I missed a bit. Can we have other stuff to from other guys rather than H’day ploughing through the same furrows all the while!

  4. All the complaints about watching a 45 minute video baffle me… I mean, good luck with the 45 hours – 45 days one might need to effect this kind of repair. :)

    1. It may have been only my complaint, but before committing to a long term relationship with a video, I’d like a brief courtship (at least) to see if it is worth the time.

  5. Carlson’s channel is in that group of YouTube channels that has to have content I need or want badly before I’ll watch it. While many need a slow presentation to keep up, I don’t. More importantly he often makes statement of fact, that I can’t find corroborating content to support. When I use the comments to make a calm straight forward inquiry, I find it removed when I return to if anyone has responded. A far out piece of old test gear, but nothing I have bench or display space for. Old or new much more useful for me will fit in the same footprint.

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