An Audio Research REFERENCE 75 vacuum tube 2-channel power amplifier was a demonstration model. Original
box and packaging come with REF75. The power amplifier is a 8 – 8.5 out of 10
condition. Tubes are fully operational
and working properly in the unit.
Shipping – Included
with purchase of the unit within most contiguous US states(lower 48 states)
only. Shipping cost is added to buyers in Alaska, Puerto Rico, Hawaii, Guam and Virgin Islands.
The Reference 75 is similar to the Ref 110 and Ref 150 in that all
three use input circuits using direct-coupled JFETs and a 6H30 tube. However,
the Ref 75 has only four Tungsol KT120 output tubes (in ARC's ultralinear
"partially cathode coupled" topology), compared with eight in the Ref
150, and eight 6550Cs in the Ref 110. The KT120—apparently the first output
tube specifically designed for audio applications—is more robust and powerful,
with greater dynamics, lower distortion, better tonal balance, a larger
soundstage, and a greater sense of presence. The Ref 75 shares the same
oversize power supply (520 joules of energy storage) as the Ref 110, but has
improved interstage coupling capacitors, and more damping material on its
capacitors and heatsinks.
The circuit design is straightforward, and careful attention was paid to
ensure that signal paths would be as short as possible. Removing the cover and
looking inside confirmed the simplicity and elegance of the circuit layout. In
fact, with only one pair of output tubes per channel, there's no need for a
The Ref 75 also sports a pair of VU meters,
which give the amp a bit of the vibe of ARC's classic D79 amplifier, from the
1970s. These double as adjustment meters for biasing each of the four tubes
individually. The meters are illuminated, and their lights can be turned off.
The Ref 75 comes with a burly, detachable, power cord fitted with a 20-amp
plug. It has 4 and 8 ohm output taps, as well as 12V triggers for input and