The OC171 Mystery (solved)

Old germanium transistors like the OC171 and later AF devices carry a ‘terrible secret’ inside their TO-7 metal can. If you switch on a ‘dead’ 1960s transistor radio containing one or more of the above mentioned trannies, try gently tapping them with a small screwdriver. In many cases the radio will crackle, burst to life or work intermittently and drop silent again after a while. Surprisingly, unsoldering a suspect OC171 from the circuit and checking its junctions using an ohmmeter will not reveal faults in the junction proper. The device will also achieve its normal electrical specifications.