AF117 transistors.

In the UK, many transistor radios of the 1960's used AF117 transistors in the RF stages. Over the years, these transistors (and others in the AF series) have failed because of internal short circuits. It has been shown that these were caused by hair-like whiskers growing out from the metal casing of the transistor into the internal workings. These were also shown to be whiskers of tin produced from the tin plating on the inside of the metal can. In the UK, most of the transistors were produced by Mullard. Has the same problem been found in transistors produced in Europe by manufacturers such as Siemens? If so, what transistors do members of the forum replace them with. There is no point using other good AF117's as the same problem will happen with the new old stock ones. In the UK, we have replaced them with other germanium transistors with similar characteristics, such as the SCAF125, although these appear to now have gone out of production. I have also used the silicon transistor BF450 with great success and without making any modifications to the circuits. They have similar biasing to the AF117.

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I usually replace the AF11x series as follows
AF112 -> AF136
AF114 -> AF124, AF134, 2SA240
AF115 -> AF125, AF121, 2SA116, 2SA240
AF116 -> AF126, AF136, 2N219, 2SA175, 2SA182
AF117 -> AF127
For all types above, AF 239s should work, too.
In critical applications it is necessary to consider detailed specifications (mainly capacities).

Respectfully, Marc

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