Jadis JA30 - Quad ESL63 .. 4,8 or 16ohms?

Sorry to disagree, but the ESL63 has an impedance that increases with sound level in the bass. At levels over 100mV the impedance never drops bellow 8 ohm in the bass. People usually measure impedance with a 1000 ohm series resistor, using levels between 10 and 50 mV, and assume that impedance does not depend on level. This is not true for the ESL63 and was published in the original HIFI NEWS review in 1981.
I have owned (and still keep) ESL63 and always used them with the 8 ohm tap of jadis, conrad jonhson and audio research tube amplifiers.

I believe the impedance of the 63's is north of 16 ohms in the bass and about 2 at 20k. That's why many amps roll over and play dead with'em.

Which tap to use is amplifier dependent. Experiment with your amp and make your own assessment. My ARC D115MkII sounds best with the 16 Ohm tap by far. I get tremendous bass response with this setup.

Microstript, Thanks for the info. I was recalling some comments made by Stereophile's Gillet maybe 15 years ago, apparently inaccurately. Maybe this explains some of my dissatisfaction with the Quads which have been in my attic for about 10 years. I was (obviously) an ignorant user. :-)

That's right Sbrown .. also my friend is getting tremendous bass response at 16 ohms taps but if you take a look at the Quad ESL63 impedance graphic ..

http://img147.imageshack.us/img147/2903/quadfig1py5.jpg

... you are gaining from 0 hertz to 600/700 hertz but you are losing from here to the 15.000 hertz and above
While theoretically with the 4 ohms tap you should gain between 600/700 hertz to the whole rest band expecially in mids and highs area .. the most important to our ears .. and where we have the most important part of musical message.

My Defy 7 sounded better on 4 ohm taps and it makes sense when one factors in that ESL's require the most power in the highs (the speaker acts like a big capacitor as a load). FWIW, I doubt if they have enough power regardless of what tap you use.