All tubes are screened for shorts, gas, and heater-to-cathode leakage (unless it’s a directly heated tube), and then tested for emissions and transconductance (Gm) on an Amplitrex AT1000 (in some cases on a Triplett 3444). Measurements are compared to published standards and/or the Amplitrex database for emissions and conductance. Diode sections and tubes are measured for peak forward and reverse current. Full-wave rectifier tubes (like 5U4, 5Y3, GZ34) are measured for peak forward and reverse voltage drops for both sections. All tubes (unless you specify Autobias mode) are measured in Fixed Bias mode, which is our default mode and the one we consider most valid in general most of the time. See the Bias page for details.