Audio Research D-76A Vintage All-Tube Amplifier, Survivor Condition

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The ARC 76A is a favorite among vintage audio collectors and tube rollers.

This one is in what we call "survivor" condition, original and unmolested.

We fitted a new set of tubes and did a light service to get it working nicely.

Cosmetic condition is good with only a few visible signs of use, please look over our photos for more info.

Audio Research D-76A Tube Power Amplifier - Manual

SkyFi Service Notes:
This unit appeared to be all original on initial inspection. After testing all of the tubes it became clear that the output tubes needed replacement. We swapped out all of the 6550's and biased them up to service manual spec. The input attenuators and jacks were also cleaned. After service, this amplifier tested clean above up to its rated 75W with ease.

SkyFi Cosmetic Notes:
• The terminal strips exhibit the typical cracked barrier guards that we normally see on units of this age. Using period correct small spade connectors or spade to banana adapters is encouraged.
• Light marking under left handle of face plate.
• Light black paint marks on face plate.

SkyFi Tube Notes:
• All 6CG7s are vintage GE, all testing well on our Modern and Professional Amplitrex AT1000 Tube Tester.
• 12AX7's are a mix of GE and RCA, also tested well on our Amplitrex.
• The original GE 6550's were at the end of their lifespan and were replaced with two matched sets of known good Svetlana Gold Label 6550 from our stock. All tubes biased to service manual spec.
• The 6550 in the power supply section was also replaced with a Svetlana tube.

Click below to add our recommended matching cables from Kimber Kable, all brand new as SkyFi is an official Kimber dealer.

Kimber Kable - RCA Interconnects

Kimber Kable - Speaker Cables

More from Audio Research:
INTRODUCED
1974

SPECIFICATIONS:
POWER OUTPUT
75 Watts per channel minimum RMS (both channels operating) into a 4, 8 or 16 ohm load from 20 Hz to 15 kHz with less than 1% total harmonic distortion

INPUT SENSITIVITY
1.5 volts for rated output

INPUT IMPEDANCE
80K ohms at 20 Hz; 30K ohms at 15 kHz

OUTPUT TAPS
4, 8, 16 ohms

DAMPING FACTOR
14 at 8 ohms (1 kHz)

DISTORTION
Intermodulation distortion: less than .5% at rated power

HUM & NOISE
More than 80 dB below rated output

POWER REQUIREMENTS
100, 120, 200, 220, 240 VAC; 50-60 Hz, 550 watts at rated power output

TUBE COMPLEMENT
(4)12AX7, (8) 6FQ7, (2 matched pairs) 6550, (1) 6550

DIMENSIONS
19" W x 7" H x 12-1/4" D

WEIGHT
52 lbs.

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 modern and professional tube 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.