Small Bear's germanium tranny tester confusion

Started by bluesdevil, December 06, 2005, 08:14:14 PM

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bluesdevil

Okay, I know Im not the brightest one here... especially with math. The Small Bear method looks to be the simpliest way to test Germanium transistors for leakage and true hfe, but I still manage not to grasp it.
    Well, I set up everything on my breadboard with battery and connect the tranny for the leakage test with my meter on the micro amp scale..... I get  .61 micro amps. Okay then I switch in the 1M resistor on the tranny's base and get 226.0.  Am I supposed to divide these two numbers for the true hfe? I'm confused because on the instructions it states the base current reading should have the same number in microamps as the battery does in volts (9 ma and 9v). .... why do I come up with such a huge base measurement number?
       I was hoping somebody here could show me an example of how the equation works with actual numbers  I gave instead of the words used in the instructions..... I think that would clear it up.
                   
       
     
"I like the box caps because when I'm done populating the board it looks like a little city....and I'm the Mayor!" - armdnrdy

bluesdevil

Here's a link to the instructions..... just scroll down to near the bottom of the page for it.
http://www.smallbearelec.com/HowTos/FuzzFaceFAQ/FFFAQ.htm
"I like the box caps because when I'm done populating the board it looks like a little city....and I'm the Mayor!" - armdnrdy

Mark F

Subtract leakage current ( .61) from full collector current, current with 1 Meg resistor,( 226). That is your True collector current. Now, if you want to be precise, measure the exact battery voltage and measure the exact value of the 1 Meg resistor. Now divide the Batt. Voltage by the resistance & that gives you the exact base current. Now divide the true collector current by the base current & that gives you the real gain of your leaky germanium transistors. I hope that wasn't too hard to understand. :icon_wink:

bluesdevil

Thanks Mark, I understand!! My mistake was in not subtracting the collector currect and leakage to get the true current reading and then divide THAT by the battery voltage/microamp conversion number. I was also expecting the leakage to be a hell of a lot more than .61 microamps. Not complaining about that, though.
      I needed some guidance, but am very happy to know I'm not totally hopeless. ... well, maybe not.
     
"I like the box caps because when I'm done populating the board it looks like a little city....and I'm the Mayor!" - armdnrdy