Audio Research Reference 300 mkII // Preowned / Tube Monoblock Amplifiers / Restored & Retubed (31301501/2)

The Audio Research Reference 300 MkII monoblocks are tube power amplification at its most unapologetically grand—massive, glowing, and absolutely regal in the way they command a system. Delivering 300 watts of pure tube authority from banks of 6550s, these amps don’t just drive speakers—they take control of them, with a combination of grip, scale, and tonal beauty that very few tube designs have ever matched.

Sonically, they’re classic ARC at the peak of its Reference-era prowess: huge dynamic swings, a holographic soundstage you can practically step into, and mids that bloom with lifelike presence without ever slipping into syrup. Highs are extended and airy, bass is shockingly tight for tube muscle of this size, and the overall presentation is one of effortless, unforced power.

Visually, the Ref 300 MkIIs radiate that iconic ARC laboratory aesthetic—industrial, purposeful, and glowing with the warm confidence of dozens of tubes ready to make music feel enormous. These monoblocks aren’t just amplifiers; they’re endgame statements for listeners who want the emotional reach of tubes and the scale of a powerhouse.

S/N: 31301501 / 31301502

RESTORATION

• Both units have new matched octets of Tung-Sol 6550's

• Both units have 3 new 6AS7 tubes in the power supply

  The following for both units:

• Installed jumpers to bypass faulty circuit board traces
• Replaced 8 resistors in power supply
• Replaced 2 mosfet power supply regulators
• Replaced 2 zener diodes in power supply
• Replaced 4 film capacitors in power supply
• Adjusted bias

FACTORY SPECS

Power output
280 watts continuous at 16 ohms from 20Hz to 20kHz with less than 1% total harmonic distortion (typically less than .05% at 1 watt). Actual maximum power available (at the point of clipping) is dependent upon the following: 1) power line voltage. 2) power line condition (ie: regulation, distortion). 3) type and brand of power output tube used. Typical power under average circumstances will be around 290 watts. Maximum power under ideal conditions will be around 300 watts.
Power bandwidth
(-3dB points) 12Hz to 100kHz
Frequency response
(-3dB points at 1 watt) 0.5Hz to 160 kHz
Input sensitivity
1.75V RMS balanced for rated output. (32dB gain into 16 ohms)
Input impedance
200K ohms balanced
Output taps
1, 2, 4, 8, 16 ohms
Output regulation
Approximately 0.8dB 16 ohm load to open circuit
Overall negative feedback
10dB
Damping factor
Approximately 11
Hum & noise
Less than 0.2mV RMS –110dB below rated output (IHF weighted, input shorted, 16 ohm output)
Power supply energy storage
Approximately 448 joules
Power requirements
105–125VAC 60Hz (210–250VAC 50Hz) 900 watts at rated output, 1200 watts maximum, 480 watts at idle, 280 watts standby
Tube complement
(4 matched pairs) 6550C power output, (4) 6H30 triodes, (3) matched 6A57, (2) 6N1P.
Dimensions
19" (48.3 cm) W x 10½" (26.7 cm) H x 23½" (59.7 cm) D. Handles extend 1½" (3.8 cm) forward
Weight
132 lbs. (59.9 kg) Net; Shipped in pairs, 410 lbs. (186 kg) per pair