Audio Research D70 MKII Tube Amplifier - Complete Set

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This is the perfect amp to get the most out of your high to medium efficiency speakers.

Coming to you in great survivor condition, you can tell this amplifier was well cared for over its lifespan.

This was originally sold as a D70 in 1984, then it was Factory Upgraded to the ARC MKII designation in March 1985. Details to confirm this are as shown on the included paperwork with your purchase.

Tested, adjusted, and working as it should throughout.

It also includes a nice set of matched Winged C tubes

Plus your purchase comes complete with the original owner's manual, service paperwork, bias tool, AND the original box.

A full collectors set!

Audio Research D70 MKII Tube Amplifier - Manual

Specifications:

POWER OUTPUT
D-70: 65 Watts per channel minimum continuous (both channels operating) at 16 ohms from 20Hz to 20kHz with less that 0.5% total harmonic distortion (typically below .005% at 1 watt).
Approximate actual power available per channel at "clipping" (both CH. OP, 1kHz): 70 Watts.

D-70 MKII: 60 Watts per channel minimum continuous (both channels operating) at 16 ohms from 20Hz to 20kHz with less that 1% total harmonic distortion (typically below .005% at 1 watt).
Approximate actual sine wave power available per channel at "clipping" (both CH. OP, 1kHz): 60 to 70 Watts.

(Note that actual RMS power output is dependent upon both line voltage and "condition" ie: if power line has high distortion, maximal power will be affected adversely, although from a listening standpoint this is not very critical.)

POWER BANDWIDTH
D-70: (-3dB points) 10Hz to 60kHz.
D-70 MKII: (-3dB points) 15Hz to 30kHz (30 watts at less than 1% THD).

FREQUENCY RESPONSE
-

INPUT SENSITIVITY
D-70: .95V RMS for rated output.
D-70 MKII: .85V RMS for rated output.

INPUT IMPEDANCE
D-70: 75K ohms, nominal.
D-70 MKII: 110K ohms, nominal.

OUTPUT TAPS
-

OUTPUT REGULATION
D-70: Approximately .4dB, 16 ohm load to open circuit.
D-70 MKII: Approximately .6dB, 16 ohm load to open circuit.

OVERALL NEGATIVE FEEDBACK
D-70: 22.2dB.
D-70 MKII: 20.5dB.

DAMPING FACTOR
D-70: Approximately 20.
D-70 MKII: Approximately 15.

DISTORTION
Intermodulation distortion: less than .1% at 1dB below rated output (80V p to p, 16 ohms - SMPTE method).

SLEW RATE
D-70: 12 V/µs.
D-70 MKII: 10 V/µs.

RISE TIME
D-70: 3 ms.
D-70 MKII: 5 ms.

HUM & NOISE
D-70: Better than 90dB below rated output (Broad-bandwidth unweighted, inputs shorted).
D-70 MKII: 85dB below rated output (Broad-bandwidth unweighted, inputs shorted)
(Peak to peak output noise envelope approximately 5mV)

POWER SUPPLY ENERGY STORAGE
Approximately 150 joules.

POWER REQUIREMENTS
D-70: 105-125 VAC 60Hz (210-250VAC 50Hz) 500 watts maximum 240 watts at "idle".
D-70 MKII: 105-125 VAC 60Hz (210-250VAC 50Hz) 600 watts maximum 240 watts at "idle".

TUBE COMPLEMENT
D-70: (2 matched pairs) 6550, (1) 6550, (1) 12AX7, (7) 6DJ8 (ECC88).
D-70 MKII: (2 matched pairs) 6550, (1) 6550, (1) 12AX7, (3) 6DJ8 (ECC88), (4) 6FQ7/6CG7.

DIMENSIONS
19" (48 cm) W (standard rack panel) x 7" (18 cm) H x 14½" (37 cm) D (front panel back).
Handles extend 1 ⅝" (4.1 cm) forward of the front panel.

WEIGHT
49 lbs. (22.3 kg) Net.
63 lbs. (29.1 kg) Shipping.

The SkyFi Testing Process for Tube Amplifiers:

We start with a visual inspection of all internal components to make sure there are no signs of stress or aging. Capacitors are checked for telltale sings of bulging or leaking, resistors are checked for signs of overheating or cracking, and tubes are inspected for signs of stress overheating or cracking.

We then power up the unit carefully and run a simple 1k sine wave while monitoring the output on an oscilloscope for signs of distortion or noise. Finally we run the amplifier to its full rated power into the appropriate resistive load provided by our Sencore amplifier tester. If there is an issue, it will usually be noticeable at this point. If it all looks clean we will often test for THD (Total Harmonic Distortion) measured by our Keithley distortion meter, and compare it against the original manufacturers specifications. The amplifier the remains powered on to "burn in" on our test bench for a few hours to make sure there are no heat related issues. If there are balanced inputs available they will also be tested.

We also test all tubes for output gain and leakage on our calibrated B&K 747 tester against the original manufacturers specifications. If needed, the tubes will be replaced from our vast NOS (New Old Stock) vintage or modern inventory.

Final testing involves pushing actual music thorough the amplifier. We've learned over time that some issues are only noticeable to a trained ear while listening to familiar source material. Our test bench has reference vintage KEF speakers that we're very familiar with which quickly reveal any discrepancies. Some amplifiers will then move into our listening room where they are tested with our in-house reference speakers of choice.