I should add that it looks like there is a 12-volt input on the bottom of each speaker, as well as some sort of knob that is very hard to turn. Thanks for your help!
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Ah. Well, you will have to get another wall-wort, of course. The control is probably the level control for the tweeter.
In principle, all you have to do is plug in the PS, connect the terminals up to an amp, and listen. I urge caution since these are old and may be faulty. (I have had on and off problems with old Janszen tweeters.) So, first plug the wall-wort into the AC by itself and see what is on the output and if it is stable. If so, connect it to the speakers and listen for noises. Good els elements will be quiet but may make very, very soft crinkly noises as they power up. After that, use your voltmeter to insure there is no DC or AC on the main speaker terminals before you connect it to a good amp.
I owned a pair of these back in the early 80's. They were nice speakers, though it was easy to bottom out the woofer on loud bass material.
Kr4 is correct. The control adjusts the balance between the electrostat tops and the cone bottoms. As I recall the crossover between the cone and electrostat elements was around 800 hz, and the nominal impedance of the speaker was 6 ohms. Nominal power handling was 100 watts, though I used more powerful amps than that without ill effects.
Each speaker had a 12v (DC I believe) wall wart power supply. I don't recall the polarity of the plug. I left them powered at all times. They draw almost nothing from the ac line.
The woofer boxes contain the audio step up transformers for the electrostat tops. The speakers provide a fairly reactive load, but I successfully drove them with a Sony integrated in 1983. They are not very efficient.
I think most amps with high end pretensions (e.g. Adcom, Hafler, Aragon, as well as more expensive brands) in the 70-150 watt range capable of driving a 4 ohm load should work. A lot of mid-fi receivers could fit this bill as well.
Let us know if you get them working, and enjoy!