KF506 
<p>NPN 75V 500mA 0.8W 100MHz
</p>
Made in  former Czechoslovakia by Tesla in 1980s.
<a href="//commons.wikimedia.org/wiki/User:Mister_rf" title="User:Mister rf">Mister rf</a>
CC BY-SA 4.0
<span class="int-own-work" lang="en">Own work</span>