56 V Zener, 500 mW — obsolete but still sourced
The 1N6018B is a 56 V Zener diode in the standard DO-35 axial-lead package, rated for 500 mW continuous power dissipation. The ±5% tolerance on the nominal Zener voltage means the regulation point falls between 53.2 V and 58.8 V — tight enough for most clamp and reference circuits in that voltage tier.
The 500 mW power rating is the thermal limit at 25 °C ambient — derate above that. With a 56 V Zener voltage, the maximum steady-state current is about 9 mA (500 mW / 56 V). The 200 Ohm maximum Zener impedance (Zzt) at the test current means the regulation voltage shifts about 200 mV per mA of load change — acceptable for many bias and protection roles. Reverse leakage is specified at 100 nA maximum at 43 V reverse bias — 13 V below the Zener knee. This ensures the diode does not conduct prematurely in a standby circuit. The DO-35 glass package is hermetic, suited for humid or corrosive environments where plastic packages degrade.