The MSC81058 is a common base hermetically sealed silicon NPN microwave transistor utilizing
a fishbone, emitter ballasted geometry with a refractory/ gold metallization system. This device is capable of withstanding infinite load VSWR at any phase angle under rated conditions.

The MSC81058 is designed for Class C amplifier applications in the 0.4 - 1.2 GHz frequency range.

NEW OLD stock from around the 1990 time frame.  This means its not a remake but the original recipe!   That means your old designs tend to work better because they are better adapted to the original transistors the design was made around.

I have 26 of these.  There are 2 manufacturers.  MSC and ST.  There is a mixture of both brands in this batch