wierd ac128 gain problems

[arielfx]

i just got a bunch of ac128 for some fuzz faces i am going to build for local musicians. i had matched 2n404a (ti) that worked great this far. i bought a big lot and war promissed by the guy that all are within 70 - 150 gain range (i bought other things from him, like transistors for my clyde mccoy and other projects). i've read "tech of fuzz face" and built the little device and I am getting very strange readings based on it. I am getting gains of 40, 36 and so on. I am pretty sure that is wrong and I can't understand what am I doing wrong over here. if anyone can help me I will greatly appreciate it.

[Fret Wire]

Are you positive your transistor tester works correctly? Did you try it with some known trannys to see if it's accurate. If it does work right, did you try different pinout combinations? Not all Ge's have the same pinout for E,B,C. If you have some 2N3906's test them. They should be in the 200-300 range.

Are the tranny leads dirty, dull, or corroded? If so, hit em' with steel wool or scotchbrite then test again. Is the battery in your tester good?

Plus, AC128's, 2n404's, and TI182505's can go that low gain wise. How did their leakage test out?

[arielfx]

i have one last pair of matched 2n404a and i tested them in the "device" and they both show up very close to the values i bought them for.
i am sure the setup is 100% ok because of this reason... i only got ac128 and i am pretty damn sure they are in the range i asked when i bought them.

about the leakage.... a few show around ~1.00 - 0.80 in the "device".

[Fret Wire]

Ok, try my other suggestions...switching around the leads. Usually where they go in the tranny, the leads look like a triangle. The middle one, usually the furthest away is the base. Try switching the emitter and collector around. Battery?

Try cleaning the leads, and testing again. And check the data sheets, those trannys usually have a minimum gain that low. Add in their age, and it's a possibility that you have a low gain batch. Maybe the seller sent the wrong batch.

[Travis]

How different were the testing environments?  Did he test outside?  Are you testing in extreme AC?

OR

Does the higher gain measurement not account for leakage?

[arielfx]

i tested them both right here at my workbench during the night, actually i tested around 10 AC128 during the night and got all kind of annoying gains around 36 - 45.
the 2N404A was tested during the night and got about the same gain ratings as it did at the guy who sold them to me (i think he got some testing device or something).

all the transistors i messed with had some leakage but it seems that the AC128 got a much higher leakage in some cases and a little higher at most cases (compared to the 2N404A).

[Roland]

When your testing the transistors are you touching them with your hand? The heat from your hand will cause the changes your encountering. Some transistors(germanium) don't react too much when holding them but AC 128's are notorious . Use latex gloves! The worst I've ever seen for that particular problem are the nte germanium preamp transistors . There 158 isn't too bad but you'd be hard pressed to find one with an hfe under 200.

[arielfx]

i am not touching them at all, i noticed that the sensitivity of these devices is something you have to see to believe
i am waiting a few minutes until the reading seems stable.