Quad 63 amp advice

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-