Re: Are your transistors growing whiskers in their old age?

greenboxmaven
 

I also enjoy restoring older complex portable radios. The Mullard transistors used in early solid state Eddystone receivers are famous for failures. Some people disconnect the case/ground lead, others connect the E-B-C leads together and apply a condenser charged to about 100 volts to the leads and the case to fry the whiskers. I felt there was nothing to lose for a more radical repair. These transistors had fairly large cases and were obviously soldered together. I unsoldered the top of the case from the header and swept the leads with an artist's brush, taking care to not touch the crystal, which was embedded in silicon grease. I then cleaned the case out with the brush, and reassembled the transistor. My success was 100% in eliminating the shorts or leakage, and about 90% overall. The receivers are working fine today. As early solid state equipment ages, this problem will become worse. To my knowledge, there has not been any problem like this with molded plastic transistors. It does occur in ICs because there is space around the silicon slab. I wonder if any of the designers back then could have imagined the equipment being restored and used 50 or more years later.

Bruce Gentry, KA2IVY

On 3/3/20 10:58 AM, Brad Thompson wrote:
Geoffrey Thomas wrote on 3/3/2020 9:53 AM:

The AF117 transistors were exhibiting this problem in the late 1970's, tin whiskers is why we had lead in solder, of course.


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