variation of the transistor was developed to increase the high frequency
characteristics. A second base wire was bonded on the opposite side of the
bar, and by biasing this second base in a negative direction, the active
base area could be reduced to gain higher frequency operation. After more
than 40 years my recollection of the frequency range of the triode
transistors is rather sketchy. They could operate of course in the AM
broadcast band and possibly much higher.
effort was directed at increasing the reliability of the transistors.
Moisture was the main problem, causing high reverse leakage and eventual
failure. Metal cans and headers for hermetic sealing was used for military
transistors, although special epoxy plastics were used commercially.
junction transistors were eventually discontinued when the epitaxial
transistor process became available. The grown junction process was labor
intensive and not easily automated. But therein lies another story!!