Euphonium Yamaha YEP-642TS NEO - ArgentA main tuning slide trigger system has been added to the wildly popular Neo series YEP 642II euphonium offering enhanced, precise pitch control. The new trigger system has been tested for extreme durability to withstand the toughest action. Main Tuning Slide Trigger System A main tuning slide trigger system offers precise pitch control as well as solid tone. The lever plate can be pressed during a performance to shift the main tuning slide downward,