8 A average, 17 ns trr — what this diode is built for
The STTH8ST06DI is a standard fast-recovery rectifier from STMicroelectronics, rated for 600 V reverse voltage and 8 A average forward current in a TO-220AC insulated through-hole package. Its 17 ns reverse recovery time places it in the fast-recovery class, not a general-purpose 50/60 Hz rectifier — it is built for high-frequency switching circuits where trr dominates the turn-off loss.
Forward voltage is 3.4 V typical at 8 A — that is a higher Vf than a standard 600 V rectifier, but it is the price for the 17 ns recovery speed. Conduction loss at full load is about 27 W, so the TO-220AC insulated tab needs a heatsink sized for that dissipation. Reverse leakage is 6 µA at 600 V, which is low enough that it does not add meaningful loss at high line voltage, but it does rise with junction temperature — the datasheet curve matters if the heatsink runs near 150°C.
No pinout surprises — the cathode tab is the output, anode is the middle pin.
Sourcing and fit — what the kit needs
This is a part you can swap on site with a soldering iron and a heatsink — through-hole, insulated tab, no ESD-sensitive handling beyond normal precautions. The marking on the body is clear enough to get orientation right once. If you need a dual-source option, look at other TO-220AC fast-recovery diodes with 600 V / 8 A / sub-20 ns trr — but confirm the package and thermal pad before committing.