worldradio: Substitutes for AF117 Germanium Transistors

AS many members will know, AF117 and similar transistors such as AF115,116, and OC170/171 were used in a great many British made radios of the 1960s & early 70s.  Due to the method of construction employed in the manufacture of these transistors, together with the fact that they are now between about 45 and 55 years old, they are prone to developing internal leaks or short circuits between one or more electrodes or between these and the metal case of the device.  This os often referred to, at least on UK Vintage Radio forums as the 'Tin Whisker' problem, and whilst a cure can sometimes be effected, I prefer to replace transistors of this type with later devices such as the AF127.  However these are now becoming scarce and relatively expensive at may £3.00 or £4.00 each in the UK, so recently I have used a less expensive alternative, such as the Russian made GT322A or 322B, often available from eBay  for around £1.00 each.  These work very well in the radios to which I have fitted them, most recently a Roberts R300 portable, without needing any circuit alterations or modifications.

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Yes, I too use Russian types. But often the RF & IF can be replaced with PNP Silicon if there is an emitter resistor. Yes, the collector current may be lower, but with suitable gain RF types, it's not a problem. In a Bush set no difference in performance using Russian Germanium or regular PNP Silicon for RF mixer oscillator and the IF amps. A Hacker set had the AM IF strip AF117 replaced with Russian types.

I think the problem was too much tin plating on inside of can. I have a perfectly working 1960s Ever Ready set with AF117 and rarely see problems with AF115. I've not seen the issue on similar can OC170  or OC171 (I forget which). I think it was particular Philips/Mullard plants at particular years. Older metal can top hat and glass Germanium are fine.

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Hello Friends.

Look also here for that Problem and a Solution. But only in german.

Mfg Knoll

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Hello,

I always use AF126 or AF127 transistors to replace AF117s. Likewise AF124s for AF114s, AF125s for AF115s and AF126s for AF116s. The AF12* transistors are expensive now but I acquired a load of them some years ago when they were a lot cheaper. I have tried discharging a capacitor through dead AF117s and heating them up with the tip of a soldering iron, both methods bring the transistor back to life ..... for a while. The problem with the AF114-AF117s was the tin lining, tin crystals form from the lining, travel through the jelly inside and eventually make contact with the electrodes, thus shorting out the transistor. The same problem existed with some contemporary Raytheon transistors.

The AF11* transistors were used in many British radios from 1961 right through the decade, however Mullard continued fitting them in their IF and FM modules well into the 1970s. These modules were fitted for example in the Roberts R707, which continued in production until 1977.  Replacement modules did thankfully have AF12* transistors.

There is at least one silicon transistor that apparently will replace an AF117 usually without modification, the BF450. However that has now become expensive too.

It's good to know that there is a cheap USSR replacement for the AF117, I shall acquire a few and see if they work OK. Thanks for the tip.

Regards ..... Howard

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