The indispensible Phil Allison tells us:

*******
The Quad ESL57 input transformer has an overall turns ratio of 292:1.

The bias voltage on the bass panels is 6.2kV and they require 18 kV
volts
p-p of audio to reach full output.

The bias voltage on the mid/high panel is 1.5 kV and requires 6 kV p-p
of
audio to reach full output.

The Quad ESL63 has a bias voltage of 5.2 kV on the panels and requires
16 kV
p-p of audio to reach full output.


To achieve this feat:

The ESL57 uses a single, modest size, C-core transformer to provide the
two
levels of audio drive.

The ESL63 uses a pair of modest size, C- core transformers to provide
the
audio drive.

*********

These are born-dangerous truth-telling loudspeakers of very great
refinement. But behind the engaging smile, it's all high tension! I am
proud to own Quad speakers. I have never heard another speaker that
gives so much longterm satisfaction.

Andre Jute
Visit Jute on Amps at http://members.lycos.co.uk/fiultra/
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