A High Level RF (HLRF) system consisting of power amplifiers (PA's) and ferrite loaded cavities is being built by Brookhaven National Laboratory (BNL) for the Spallation Neutron Source (SNS) project. Four cavities were built and are being tested. Each cavity has two gaps with a design voltage of 10 kV per gap and will be driven by a PA directly adjacent to it. The PA uses a 600 kW tetrode to provide the necessary drive current. All the PA's were built and are being tested at BNL prior to shipping to ORNL. A dynamic tuning scheme used to help compensate for the effect of beam loading was implemented and tested.