Transistor leakage

[ckim715]

Hey all,

just curious; what is considered "high leakage"? I ordered some AC176s from the fleabay, and they range from .3-.4 leakage (I'm assuming 300-400 mA).

[midwayfair]

Depends on the gain, but anything above 300uA is pretty high for a transistor of 100hfe or lower. 500uA is about the highest I'd ever consider using for anything up to ~130hfe, EXCEPT in a circuit that requires leakage current to function, like a TB MkI or MkII, or for lower gain leaky pieces, the Harmonic Percollator. So don't just chuck leaky transistors. They might be useful. They will also work as diodes if they're ridiculously leaky (1mA or so ...).

[ckim715]

Thanks for the info. I'm using the AC176 for a Cosmopolitan build, which to my knowledge uses a fairly leaky AC176 to begin with. Hoping one of these will work out..

[selfdestroyer]

Depends on the gain, but anything above 300uA is pretty high for a transistor of 100hfe or lower. 500uA is about the highest I'd ever consider using for anything up to ~130hfe, EXCEPT in a circuit that requires leakage current to function, like a TB MkI or MkII, or for lower gain leaky pieces, the Harmonic Percollator. So don't just chuck leaky transistors. They might be useful. They will also work as diodes if they're ridiculously leaky (1mA or so ...).

Nice explanation Jon. I always wondered what a base would be for quick testing with the Peak DCA.

Cody

[miter53]

"How much leakage is too much? 100uA is common, 200 happens pretty often. More than 300uA means the device is suspicious, and more than 500uA I would say is bad."

From R.G. Keen's "Technology of the Fuzz Face"

[Bret608]

Thanks for the info. I'm using the AC176 for a Cosmopolitan build, which to my knowledge uses a fairly leaky AC176 to begin with. Hoping one of these will work out..

You should be fine with these for a Cosmopolitan. If you have one 50-60 hfe that would probably be best regardless of leakage. Paul (JakeFuzz) sent me a 2n1304 in that range, and it sounds great paired with a high-gain BC108 for the silicon (680-ish hfe).