Rogue Audio Stereo 90 Tube Amplifier - $2000

Rogue Audio Stereo 90 Tube Amplifier - $2000

It has power to spare, a beautiful round mid-range and nice, controlled bass. The imaging is outstanding as well. As a longtime audio enthusiast, I have always held an appreciation for tube-based gear. 

Rogue Audio Stereo 90 Tube Amplifier
Rogue Audio Stereo 90 Tube Amplifier - $2000

Four classic 6SN7 tubes
Classic 6SN7 tubes

Rogue Audio have consistently introduced new tube audio products since the late 1990s. I like their approach of merging classic tube audio with modern internal components and design.
bias adjust in the Stereo 90
Bias adjustment meter in the Stereo 90

From the Rouge Audio Owners manual available here

The Rouge Stereo 90 features a Triode/Ultralinear switch:

The output transformer of a tube amplifier acts as the electrical interface between the very
different impedances of the loudspeaker and the tube circuitry. There are three
fundamental ways that the output transformer can be connected to the tube circuit.

1) Tetrode or Pentode connection – In this configuration, the highest power level
is achieved but at the expense of significantly higher distortion levels.
Practically speaking, this mode of operation is sonically inferior and has been
disregarded in the Stereo 90 design.

2) Triode connection – With this configuration, the lowest level of distortion is
achieved but at the expense of output power. In the case of the Stereo 90, its
power level in triode is high enough that it will likely provide plenty of power
for almost any speaker load.

3) Ultralinear operation – With this configuration, power levels near those of
tetrode mode are achieved with low distortion levels that approach those of
triode operation. For loudspeakers that demand very high levels of power,
ultralinear should provide excellent sound and plenty of power.

The triode/ultralinear switch allows the user to operate the Stereo 90 in either of
the two modes. In general, the sonic differences are subtle but for a given
loudspeaker one mode is likely to sound better than the other. There is a
complex relationship between the output transformer and the crossover network
so try both and see which one works best in your system. This switch can be
operated while the amplifier is playing but you will hear a small relay noise
through the loudspeaker. 

Product Description

Stereo 90 
General Features:
Ultra-wide bandwidth output transformers
Massive fully regulated high voltage supply
Matched quad output tubes
Heavy-duty gold plated RCA inputs
Heavy-duty gold plated binding posts
User selectable 4 and 8 ohm output taps
User selectable triode or ultralinear output
(4) KT88/6550, (2) 6SN7, (2) 12AX7 tube complement
Built in bias meter
Integral tube cage
Machined aluminum faceplate
Mechanically isolated transformers
Heavy (2 ounce) copper circuit board
All precision components
Fully tested, burned in, and auditioned
3 year limited warranty (6 months on tubes)

output power: 90 WPC minimum
input impedance: 200K Ohms
frequency response: 5Hz - 50KHz ± 1dB
THD: 0.1 % @ 1 W, 1% THD @ 90 W
input sensitivity: 1.0V RMS
dimensions: 18"W x 15¾"D x 7"H
weight: 60 lbs.
power requirements: 115/230V - 50 - 60Hz