Measuring hfe in transistors?

[AC30Dirty]

hey guys, i just got some transistors from small bear to install in my wah. I'm not to familiar, working with transistors though. My question is how do I measure the hfe of the tranny's so i know which ones are close in value. Can I do this with a multimeter? They will be going into a crybaby and a vox V847. Also how do i know which legs are what. (meaning emmiter, collector...) The transistors are BC109's, BC109C's and BC108's. thanks

[calpolyengineer]

Some multimeters have that measurement, most cheaper ones do not. I'm not aware of a way to measure hFe without the multimeter, but it must be possible. As for the pinouts, you should check the datasheets on those. The site I use is alldatasheet.com.

-Joe

[pyrop]

Hey there.
The transistors you got from SmallBear are they the real things in a metal can or are they the workalikes?
Yes you check hfe via a mulitmeter. The emitter on the BC107,8,9's is usually indicated by the tab.
BTW yes they are NPN! But it is always best to check the datasheets first.

pyrop  

[R.G.]

1. Go read the info at GEO on measuring hfe
2. If they're germanium, read the info and make the hfe/leakage tester at GEO
3. Multimeters do a quick and dirty gain measurement. Next time you look at one in your multimeter, leave your fingers on it, heating it up to skin temperature and watch hfe change.
4. Never, ever put transistors in a circuit until you know for certain what the pinout is. If you don't know, you can search for "{partnumber} datasheet" on google and most likely turn one up. You will only confuse yourself if you have not checked the pinout.
5. Close in value to WHAT? Do you know what value is needed?

[formerMember1]

5. Close in value to WHAT? Do you know what value is needed?

ac30dirty: For a wah i would use around 400hfe.. one transistors affects the Q and the other affects the sweep,... usually use higher one in Q1, but what really tweaks it right is adjusting how far apart they are from each other,.. like Q1 390 and Q2 405 or Q1 402 and Q2 435...

*edit*
read www.geofex.com & search forum... 

[jeffy]

I see how to check hfe for germanium transistors, is it the same way for silicon ones?

[AC30Dirty]

Thanks everybody for all the feedback. I placed some sockects where the transistors go and I'm tweaking with different values as we speak. I'll get back to you on this post and let everyone know how it went. Thanks

[Dave Eason]

measure the base current, then measure the emitter current, and isn't Ie = G x Ib ? Where G=Hfe.  Actually, Ie would equal the collector current plus the base current right? Assuming this is all for bipolar transistors..