On Thursday, March 29, 2018 at 10:47:54 AM UTC-4, wrote:
I believe that it will need at least 35W per channel.
The 520F has 100 wpc/rms/8 ohms.
The Quad ESL63 gives 86dB @ 1 watt @ 1 meter. Not very efficient.
35WPC *will not* sound anything like 100 WPC. You will miss that headroom. Badly.
There are a goodly number of 60+ & 75+ WPC tube amps out there, and I would start there.
Here is one source for non-Chinese *NEW* units at reasonable prices.
http://www.tubes4hifi.com/bob.htm
Peter Wieck
Melrose Park, PA