Front and center: 2N168A
Very Ancient Germanium NPN Transistor
Type Designator: 2N168A
Material of Transistor: Ge
Polarity: NPN
Maximum Collector Power Dissipation (Pc): 0.065 W
Maximum Collector-Base Voltage |Vcb|: 15 V
Maximum Collector-Emitter Voltage |Vce|: 15 V
Maximum Collector Current |Ic max|: 0.02 A
Max. Operating Junction Temperature (Tj): 85 °C
Transition Frequency (ft): 3 MHz
Collector Capacitance (Cc): 5 pF
Forward Current Transfer Ratio (hFE), MIN: 40
Noise Figure, dB: -
Package: OV17
https://alltransistors.com/transistor.php?transistor=1193
And it is Ancient! I’m sure I have a substitute on hand, but in a different package. I might even find one of those listed in the photo, if I dug around.
Germanium is a low current device. Largely displaced by silicon.
“The main difference between germanium and silicon transistors in switching circuits, be they either PNP or NPN transistors is that VBE for small germanium is about 0.3 volts whilst those of silicon are about 0.7 volts. Also germanium are more sensitive to heat than silicon and can end up in thermal runaway and destroy themselves. “
Yep, good old germanium transistors. Guitarists love them in their fuzz pedals and seek them out. That’s how I first learned about them...