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

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

General
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 that there are no signs of heat stress or damage. Capacitors are checked for telltale signs of predictive failure including bulging, shrunken wrappers, or physical leakage. We also inspect the PCBs for discoloration from resistors or transistors that may have been running hot. On vintage units we often spot check select capacitors for value and ESR. 

If the amplifier passes visual inspection, we move on to a controlled power on sequence using a Sencore safety analyzer to monitor current draw in real time. Once the amplifier is determined to be safe to operate, we connect it to full AC mains for function and power testing. We connect the speaker outputs of the amplifier to a Sencore PA81 Power Analyzer which acts as a dummy load, DC offset monitor, and oscilloscope interface. We start with a low level 1KHz test signal at the amplifier’s input and slowly increase its amplitude while monitoring the output on an oscilloscope for signs of noise, clipping, distortion, or improper channel balance. We continue increasing the signal level until the amplifier reaches clipping. At this point we take an output power measurement and compare it to the spec sheet of the amplifier to verify proper performance. If the device under test has both balanced and single ended inputs they are both tested at this time. We finish off the bench evaluation with a 1KHz square wave check and a 20Hz to 20KHz sine sweep to assess the amplifier’s frequency response characteristics. This battery of tests will usually reveal if the amplifier has any issues that need further attention. 

Before the device leaves the bench, we perform a listening test with actual music using a variety of preferred test tracks. Our benches are outfitted with familiar monitor speakers which help us identify inconsistencies that will not always show up on our test gear. The main things that we are listening for are hum or noise with no signal present, proper center image, clicks, pops, or any other obvious undesirable audio characteristics. 

If the unit passes all of these tests it is moved to our long term testing rig where we simulate real word operating conditions for 6-8 hours. This allows us to monitor the unit for signs of thermal runaway or intermittent issues that only crop up when the unit has fully come up to temperature.