Picker International (Crown M600) 600W Class A/B Gradient Monoblock Amplifiers - NEW Price

$1,999 $2,199

Crown fans may be familiar with the M600 monoblock amplifier, producing 600W into 8 ohms with brute force Class A/B.

Apparently this amplifier design was well suited for a variety of industrial and medical applications. Variations of the design were sold under brands such as AE Techron and Picker International.

What we have here is a pair of Picker International 8506 Gradient Drive Amplifiers, likely produced for use with MRI and X-Ray machines. We also have several of these amplifiers available.

They were acquired from an avid audio collector who was planning out a massive 7 channel Altec system. We believe he may have intended to use these amplifiers for bass amplification.

Our bench tests showed that both amplifiers test clean to 630W into 8 ohms before clipping. They have surprisingly flat frequency response and are completely usable as full-range audio amplifiers.

These amps have a slot on the front with unpopulated PCB's. Looking at the crown M600, it appears as though different card and control variations could be inserted to offer additional features such as level attenuation.

These amps also feature BNC style professional input connectors. We've installed BNC > RCA adapters to allow them to interface with conventional audio interconnects.

This set passed our routine bench listening tests and operated with no audible noise or hum.

Cosmetic Notes: Some screws are missing. One amplifier had some of its large filter capacitors replaced with Crown branded units.

Multiple units available so please let us know if you need more than a pair.

From the web:
"Each unit has 2kW of transformer capacity and will drive its rated load all day long without blinking. Designed for extreme duty cycle applications like medical MRI coils and shaker tables, these make incredible subwoofer amps, having very high damping factors and output of nearly 600 Watts into 8 Ohms, 800 Watts into 4 Ohms and 1200 Watts into 2 Ohms" 

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

The SkyFi Testing Process for Solid State 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 transistors are checked for signs of stress or damage.

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 everything reads 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 then 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 be also be tested.

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.



Original Box





Not Applicable


Yes - Power

Physical Condition


Working Condition


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