Repairing the mysterious antique electrostatic tweeters in a Grundig Radio

How do these mysterious tweeters work? What goes wrong in them? Are they even worth repairing? Here's a video on how to repair antique electrostatic tweeters used in Grundig equipment.
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[vaughnc]

Finding info on these Grundig electrostatic tweeters has been difficult. It’s fitting that I tore one apart yesterday, and then 24 hours later blindly discovered your video of how to do it. I’m waiting on a proper dummy load to get here so I can test without the woofer to see if I got them working or not.

[kevinsweeney]

I don't think it's supposed to be that subtle. The before/after on the Telefunken electrostatic tweeter repair video is huge. Have you replaced the two caps in series with the tweeters?