What tube amps for the Quad ELS 63

The speaker needs an amplifier that can do a good job of making constant power with respect to its impedance. The reason for this is that the impedance curve is based on a capacitance, and so is decreasing as frequency increases. At the same time the impedance is quite high in the bass region, and many amplifiers will have difficulty making power at these frequencies as a result.

So. much like the 57, but with greater power handling ability, the speaker has always been a good combination with OTLs, going back to its initial introduction. OTLs are one of the few amplifiers that can make power in the bass region of the speaker, without sacrificing the highs. Its been my experience that the speaker can manage 100 watts alright, and it seemed a lot more fun with the extra power.

Quad II's or Quicksilvers.

I used a Cayin 50 with great results in a smaller room. When the 63's went to the living room I used the Quad 909/99 with excellent results. I absolutely agree with an earlier post that the 63's should not be toe'd in...keep them square to the room. If you need to adjust soundfield play with distance between the speakers and the distance from the walls. They aren't too finicky but when they are set up right and played at the right volume they are great!

Atmasphere has made an excellent point. After abandoning the 63s for the big Sound Labs I switched from Jadis to his OTLs and have not had a single regret since.

(Audiophiles are fickle and unfaithful. Divorce is cheaper in this field, though not quite inexpensive all the same.
Regarding my new gear (SLs and OTLs) I've been faithful for over four years now and intend to remain so.

II40 or 909.
for the period of more then two decades I have tried various ss/tube amps for 63,988,2805 and to my ears they work best with Quad electronics. I owned CJ pV5/Mv50,electrocompaniet,counterpoint in the eighties,then Krell,Pass Labs,Bryston,Athmasphere,Graaf etc
but always after longer or shorter time interval (sometimes a few days,sometimes a couple of months) i start feeling the fatigue, which never comes with Quad electronics.Give you a favour: try some Quad amp before spending money elsewhere !