[CuriousMarc] was restoring an old Model 19 TeleType. The design for these dates back to the 1930s, and they are built like tanks (well, except for the ones built during the war with parts using cheaper metals like zinc). Along the way, he restored a hefty tube-based power supply that had two very large electrolytic capacitors. These dated from the 1950s, and common wisdom says you should always replace old electrolytics because they don’t age well and could damage the assembly if powered up. [Marc] didn’t agree with common wisdom, and he made a video to defend his assertion which you can see below.
If you look at the construction of electrolytic capacitors, one plate of the capacitor is actually a thin layer that is formed electrically. In some cases, a capacitor with this plate is damaged can be reformed either by deliberate application of a constant current or possibly even just in normal operation.
Of course, [Marc] agrees sometimes a capacitor is done for and has to be replaced. But he is saying that if you test it and it is good enough, it will get better with use. He also shows a capacitor that is starting to fail in a way such that he did replace it.
We get the idea [Marc] was a bit peeved at the comments on his previous video about his failure to replace the capacitors. He’ll get no sympathy from any Hackaday authors though. We have covered how to reform electrolytics before. We’ve also examined the insides of different capacitors, which is a good start to reasoning about how they might fail.