UPDATE: 2024.03.03 They’re now available in the Hoppe’s Brain Shop!

Here’s a (literally) cool solution to replace those MT-200 output transistors in your vintage amp or receiver! These adapters equal the excellent thermal performance of MT-200 devices, using commonly available TO-3P or TO-247 transistors.

The entire adapter is solid copper all the way through; there is no insulating layer. The TO-3P transistor is simply surface-mount soldered to the adapter, using solder-paste and hot-air. The backplate (collector) is connected to the copper body of the adapter.

MT-200 transistors have terrific thermal performance, due to their large copper heat-spreader. In fact, most MT-200 devices are literally a TO-3P back-plate soldered to a larger MT-200 heat-spreader.

MT-200 devices are often rated for an additional 50W dissipation versus a TO-3P version of the same transistor, and this is entirely due to the action of the heat spreader. As you can see, a TO-3P soldered to one of these adapters must logically be identical in performance to a genuine MT-200 device. (I’ll be testing this assertion.)

And I have a version for those weird 4-pin NEC 2SD-746A and 2SB706A, used in Pioneer SX-980, SX-1980 receivers, and a few others.

Available next week!