Re: Graetz Sinfonia Tweeter
Here's a little more info about the Piezo-tweeters.
This has obviously nothing to do with your Graetz, and then again..
When looking at the schematic you've posted it's clear that your speaker is charged with 260VDC, consistent with an electrostatic speaker.
As you will see the Blaupunkt has a blocking capacitor in series with the Piezo-tweeters as they don't need the DC charge.
So this will perhaps be a safe way to spot what variant was used in these vintage sets.
/Torben
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