Quad 63 amp advice

Triode.

Unless your listening room is small or you listen at relativly low volumes 25 watts is really not enough. The speaker is not hard to drive but assuming an average listening room and volume level around fifty watts/ch would be a resonable starting point. IMHO, tubes are the way to go. OTL's would be the amps of choice. The Atmasphere M60 would be a nice choice at a reasonable price.

To add to Jtinn above, you can ask Detlof: he's using a number of Quads in his system and is, hence, very experienced on this subject.

I used to like the sound a pair of EAR 519's produced on 63s -- long time ago!

The very best I have heard my Quad US Monitors sound was with the Unison Research Smart 845 monos...25 watts per channel single ended. However, my experience is that with the Quads 25 watts from one amp may work while 25 from another may not. I also thought that the Cary 572s sounded good...20 wpc...but not in the same league with the Unison.
Good luck...you just have to try amps until you find the one that sounds "golden" to you in your price range.

I think you will be fine as long as the amp is OK with the impedance of the Quad.

I ran ESL-63s with a Beard P-35 (2x35W PP EL34), it sounded lovely and I never felt short on power.

Jon

I have tried several amps on mine, including a triode amp - ARC Classic 60. It matched well.
Tried a muscle amp - Plinius SA-250 - not particularly impressed.
Pass Aleph 3 was nice, but too lacking in bass for my liking.
Currently using Spectral DMA-90 which is probably best of all, and is beautifully transparent (with the right cables).
Good luck
Ron

I've also used Spectral DMA-50 bridged mono amps on my quads for a dozen years with great success. Both Quads and Spectral gear are Crosby Modified-