18 V regulation in a field-swappable package
The 1N6006A/TR is an 18 V zener diode from Microchip Technology, rated for 500 mW continuous power in the DO-35 axial-lead package. That 18 V nominal is the voltage it holds across its terminals when reverse-biased into breakdown — useful for clamping a supply rail or providing a local reference on a board that sees -65°C to 175°C ambient. For a precision reference circuit that needs tighter than 5%, you reach for the 1N6006B (5% grade) instead; for a general-purpose clamp or bias rail, this grade keeps the BOM cost down without over-specifying.
Leakage and forward drop — the real-world limits
Reverse leakage is specified at 100 nA maximum when 11 V is applied across the junction — well below the breakdown knee. That low leakage means the diode draws negligible current from the circuit it is protecting until the voltage actually exceeds 18 V, which matters for battery-operated gear where every microamp counts. Forward voltage is 1.1 V maximum at 200 mA forward current. If the diode sees forward bias in the application (e.g., reverse-polarity protection), the 1.1 V drop at 200 mA dissipates 220 mW — within the 500 mW power budget, but the junction temperature rise from that dissipation plus the 175°C absolute max leaves a safety margin of about 50°C at 25°C ambient.
DO-35 axial — swaps without a hot-air station
You can cut the old part out of a board and solder the replacement in with a standard iron — no hot-air station, no preheater. That makes it a field-service-friendly part for repair techs who carry a kit of common zeners. Tape & Reel packaging (the /TR suffix) means the parts come on a reel for automated insertion or pick-and-place into a carrier tape. For a bench repair or a small-batch build, the reel is less convenient than a cut-tape or bulk tube, but the parts are the same silicon either way.