The STK411-210E is a fantastic piece of audio history. It delivers warm, robust 50-watt stereo sound with minimal external components. While it is sensitive to heat and increasingly rare, a genuine unit used within the datasheet limits (±37V, 8Ω, good heatsink) will last for decades.
This is a split supply IC. You need a transformer with a center tap (e.g., 28V-0-28V AC). After rectification and smoothing, this gives approximately ±39V DC. stk411210e datasheet
Note: Specifications vary depending on the specific application circuit and heatsink thermal capacity. The STK411-210E is a fantastic piece of audio history