BC108C Gone Wild

[RRJackson]

Anyone got any idea why I'd get a reading like this from a BC108C? Normally these seem to have an hFE of about 250. Some of them are as low as 50 or so. Some as high as the mid-500s somewhere. This one...

[Gus]

Test it with a DMM set to diode test, do the following four tests note the meter reading
+ probe on base - on emitter
+ probe on base - on collector
- probe on base + on emitter
- probe on base + on collector

[PRR]

Replace the battery in the Peak. (It may get stupid when batt is nearly dead.)

[RRJackson]

Test it with a DMM set to diode test, do the following four tests note the meter reading
+ probe on base - on emitter
+ probe on base - on collector
- probe on base + on emitter
- probe on base + on collector

+ probe on base - on emitter = 1.246v
+ probe on base - on collector = .687v
- probe on base + on emitter = OL
- probe on base + on collector = OL

What does that mean? Why would those second two measurements be out of range?

[Gus]

The four measurements are an old school way of testing transistors
Note the two diode drop voltage base to emitter compared to the Base to Collector
It could be a Darlington transistor and not a 108

Test a 108 that checks correctly on the peak for the voltage from base to emitter

[RRJackson]

HA! You are correct! It is NOT a BC108C! If I wasn't old and half-blind I'd have noticed. It's some kind of photo-transistor. It has that transparent dome thingee on top of the metal encapsulation. Yikes. Musta got into that batch of trannies and I never noticed the difference. I'm sorry about that.

-Rob

The four measurements are an old school way of testing transistors
Note the two diode drop voltage base to emitter compared to the Base to Collector
It could be a Darlington transistor and not a 108

Test a 108 that checks correctly on the peak for the voltage from base to emitter

[tacobender]

Do these devices work for getting a correct hfe on a germanium transistor, I've been thinking about getting one.

[RRJackson]

Do these devices work for getting a correct hfe on a germanium transistor, I've been thinking about getting one.

Yeah, they're absolutely awesome. You don't even have to attach the leads to the correct legs of the transistor; it automatically identifies them. Then it gives you the hFE factoring in leakage. SO handy. I can evaluate and match up a few dozen transistors in a tenth the time it used to take.

-Rob

[JustinFun]

Do these devices work for getting a correct hfe on a germanium transistor, I've been thinking about getting one.

As Rob says, they're great. If you use germanium at all you will never ever regret getting one.

[hymenoptera]

I own both the DCA55 and the DCA75 Pro, and I might suggest spending a little more and get the 75 if you think you'll want to measure JFETs or would like to see curves on anything. The 55 doesn't do JFets and doesn't have the option of USB to computer software for curve tracing. If all you want is to read hfe on silicon bjts and germanium then the 55 is fine.

But yeah, they're both great little (expensive!) tools, and get used all the time here.

[duck_arse]

stick that transistor under a big magnifying glass and peer inside, you might see the two die making it a darlington.