QUAD Vacuum Tuber Amplifier Systems QUAD II-FORTY - Manual (Page 4)

II-
eighty
The Quad The Latest addition to the Quad Valve Power amplifier
series is the long-awaited Quad II-eighty amplifier. The
perfect partner to our latest ESL speakers, the II-eighty is
not merely a nod in the direction of retro styling, it’s a
modern high-performance amplifier designed by one of
the most famous tube-amplifier designers in the world
(Tim de Paravicini) using more than a little inspiration
from the original Quad II amplifier.
The Quad ll-80 is an 80 watt mono power amplifier
following in the tradition and philosophies of Peter Walker.
The output section consists of 4 KT88 valves running as
two pairs in push pull with the hallmark Quad topology of
partial cathode loading in the output transformer.
This method reduces distortion when compared to the
usual Ultra Linear or triode methods, however, it does
require a greater grid driving voltage. This is achieved,
again in true Quad fashion, using a balanced pair
input stage.
The output transformer has been designed to improve
high frequency performance and accurately balance
the two push pull halves. Also the transformer has been
designed to make sure that full output is realised at the
bass frequencies down to 20 hz.
Each output valve has its own cathode resistors to
provide reliability and self-matching. The screen grids of
the KT88 valves are run from a lower voltage, again for
good reliability. The whole amplifier has a total of only
16 dB of feed-back providing good stability into virtually
any known loudspeaker and especially the famed Quad
electrostatic loudspeakers.
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