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Replacement Amplifiers

Unholtz-Dickie offers a full line of high performance Class D switching power amplifiers. These amplifiers used in UD's new shaker systems, are offered as replacements for older, water-cooled vacuum tube amplifiers or bipolar transistor amplifiers. Many vibration test systems purchased over the past 30+ years include low efficiency, water cooled Power Amplifiers housed in large multi-bay consoles. These old technology linear amplifiers consume large amounts of 3-phase electrical power, occupy excessive amounts of valuable floor space and require environmentally "unfriendly" water cooling systems. All of these problems have one common solution - A new SA Series Power Amplifier from Unholtz-Dickie!
SA Series Power Amplifier

Key Benefits Include

  • Totally Air-Cooled
  • Modular Design (15 to 480 KVA)
  • Class D, High Efficiency Switching Design: >90% Efficiency
  • EMI Shielded Cabinet
  • Small Footprint
  • Increased Shock Performance
  • NO Transformer Coupling
  • SA-Command Link for Remote Operation from APEX SL
  • Very Low Maintenance

SAI Series

The SAI Series Power Amplifiers have become a benchmark in class D power amplifier design for electrodynamic shakers. Representing the latest technology in MOSFET and IGBT circuit design, these amplifiers provide one of the most efficient totally air cooled designs in the industry. These compact amplifiers are modular in design, and can be configured from 15 KVA up to 480 KVA in one to four bay consoles.

The amplifier includes a comprehensive operating/status meter panel for pushbutton startup and monitoring of critical amplifier/shaker status, voltages and currents. A simple pushbutton selection provides for external startup through a simple contact closure. In addition, all SAI Series Power Amplifiers can be configured with the new SA-Command Link Interface which allows communication with APEX SL Vibration Control System for starting, stopping and monitoring the amplifier/shaker system.

Advanced designs in filtering and shielding have provided significant improvements in the reduction of radiated and transmitted emissions (EMI). The standard SAI Series power amplifiers are provided with a special EMI shielded console designed with minimal penetrations including metal gaskets on all external joints, special plating for better electrical continuity and corrosion protection, EMI shielded cooling ducts, and 3-phase line filtering.

Elimination of Water Cooling

SAI Series Power Amplifiers are 100% air cooled, eliminating cooling water consumption and the related expenses associated with maintaining cooling towers (chillers), pumps and leaky pipes/hoses.

Reduced Power Consumption

SAI Series Power Amplifiers are over 90% efficient and typically use less than half the 480V (380V) 3-phase power that existing linear power amplifiers consume for the same test. Further power savings are achieved due to the reduced load on the cooling tower (or chiller) which previously had a combined load from the shaker and power amplifier. A typical 20,000 lbs force vibration system with an old technology linear amplifier rejects about 170 KW to the cooling water loop at maximum force output. After replacing the original linear amplifier with an air cooled SAI Series Amplifier, the total system heat rejected to the cooling water loop is only 50% of the original load. This results in major savings at the cooling water tower (chiller). Conversely, this extra 85 KW of cooling capacity could be used for other lab equipment.

Reduced Floor Space

A typical water cooled linear amplifier rated at 120 KVA output is housed in a 5 or 6 bay console, occupying approximately 30 sq. ft. of actual floor space plus another 25 sq. ft. for required wall clearance. The Model SAI120 (120 KVA) is housed in a 1 bay console (5 sq. ft. plus wall clearance). This floor space advantage speaks for itself.

Increased Random and Shock Performance

The SAI Series Amplifiers typically provide at least 10% more random vibration performance and 50% more shock performance than a comparable linear amplifier. Contact UD for the performance characteristics on your specific shaker/amplifier combination.

Spare Parts and Service Support

Some amplifier suppliers have officially discontinued parts and service support for their water cooled linear amplifiers, thereby forcing their customers to find a replacement solution. SAI Series Power Amplifiers are available to replace most brands of linear amplifiers (see table below). Please contact UD for a recommendation and prompt quotation for your system.

SAI Series Power Amplifiers can be used to upgrade older UD shaker systems, as well as those from other manufacturers.


  1. Final KVA requirements are based on the shaker efficiency, manufacturer and age.
  2. Force ratings are estimates based on typical input KVA ratings. Actual force values will depend on shaker efficiency, manufacturer and age.
  3. Estimated force rating based on sine and random testing. Shock performance will be higher.

UD Replacement Power Amplifiers have been interfaced to a variety of shakers from different manufacturers. Typical large, older competitor systems were supplied with messy hydrostatic bearing oil supplies, large heat exchangers, and massive matching transformers. UD SAI Series Amplifiers are DIRECT COUPLED, eliminating the need for the transformer. In addition, the neatly packaged shaker heat exchangers and oil supplies will reduce floor space by up to 80%! A partial listing of competitive shakers that can be easily driven by SAI Amplifiers includes:

Shaker Models
860 C210 249
890 C220 300
964 C150 335
984 C90 340
994 C60