Obsolete — sourcing the 24V 500mW DO-35 Zener
Microchip Technology lists the 1N6009B as Obsolete.
Zener voltage is 24 V nominal with a ±5% tolerance — the actual clamp voltage for a given part lands between 22.8 V and 25.2 V. That spread matters when the Zener sets a supply rail or protects a 24 V bus; the worst-case low side may not hold off a 23 V rail. Power dissipation is 500 mW maximum. In a 24 V shunt regulator, that limits the steady-state current to about 20 mA — beyond that the junction temperature climbs past the 175°C absolute maximum. Maximum Zener impedance (Zzt) is 62 Ohms — this is the dynamic resistance at the test current. A 62-Ω Zzt means the regulation voltage shifts about 62 mV per mA of load change, so this part is a clamp or protection device, not a precision reference.
DO-35 axial — what it asks of the board
The 1N6009B comes in the DO-204AH (DO-35) axial-lead package, supplied in Bulk. Through-hole mounting with 0.020-inch diameter leads — the hole size on the PCB should be 0.031 to 0.035 inch for a reliable solder fillet. Operating temperature range is -65°C to +175°C, which covers military and industrial thermal profiles. The 175°C junction limit is the hard ceiling; derate power above 25°C per the standard Zener derating curve.