The 1N6634 is a 3.9 V zener diode in an E axial through-hole package, rated for 5 W continuous power dissipation.
Electrical characteristics for BOM fit
Maximum impedance (Zzt) is 500 Ohms; reverse leakage is 175 µA at 1 V, and forward voltage drop is 1.5 V max at 1 A.
