AF117 is there a definitive answer!

[davegsm82]

This may be a wild suggestion, but has anyone considered removing the grease and filling the can with (decent quality) Epoxy Resin?

The Tin whiskers will be NO match for Cured epoxy resin.

I dont think i've encountered one with whiskers yet, only got a very small RAACO drawer filled with germanium so there might be one in there to experiment with.

Dave.

[jim_jobe]

Originally Posted by Billy T

I consider that there is too much risk in the cap-flashing or soldering iron 'cures' and since AF117s and their ilk are an endangered species these day, it behoves us to protect them if we can.

I have had great success using two or three used mini-9volt batteries in series, joining ebc together (properly, by soldering if you can) and applying the voltage between them and the screen wire which connects to the can.

You are only trying to fuse tin-whiskers of microscopic thickness, and this method simple melts them, hopefully leaving a small ball on either end to inhibit regrowth. The cap-discharge method killed the transistors completely on several attempted cures and I think there is just too much energy floating around for comfort with that system.

You could probably even do this in-situ if access is good, just bridge ebc temporarily, nip the screen wire, apply the volts then reconnect the screen and remove the bridging. This has worked well for me on a number of used and NOS AF117s and I believe it is much safer and more reliable than bashing, heating or blasting!

Cheers

Billy

I always use a single PP3 and never had it fail to zap the whiskers. Just be careful not to connect it across base and emitter (or collector). I twist b,c and e together and then connect the battery between this and the case or screen lead. The cure has lasted for a couple of years at least so far on quite a few transistors but it's easy enough to do again if they regrow. I know you can sub AF125, etc but they don't look as good to my mind. It depends what you want I suppose,
Jim