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Author Topic: R.G.'s germanium tester  (Read 4505 times)

bobhill

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R.G.'s germanium tester
« on: August 07, 2012, 08:55:21 AM »
For those of you who are also putting together some old germ based effects, this simple device helps in determining leakage and hfe for germanium trannies. I built it one day when I was involved in testing and sorting a batch of a couple of hundred PNP and NPN germaniums I had acquired, and got to thinking about what I was doing, i.e. plug the transistor into the breadboard, power up, let it stabilize, take reading, hook the 2.2M resistor, take another reading, rinse and repeat etc. etc.

For the circuit I refer you to R.G.'s article on Geoefx about the tech of the Fuzz Face, his explanation is a lot more clear than I could manage in the space here. I had all the parts but the connectors in the parts stash, those came from Radio Shack.

For a quick explanation, the trim pot is a 5k set for 2.47k measured with my Fluke 8060a. Plug in the trannie, turn on the switch and let stabilize. The short leads plug into the meter. Labeling on the trace side shows orientation. Record the reading. The push button adds the 2.2M resistor into the circuit as per R.G.'s explanation. Take second reading, subtract the first and multiply by 100 for hfe. The circuit is normally set for PNP, for NPN reverse the battery and meter connections. It took me less than an hour to draw the traces with a sharpie, etch and then build the thing. I use a battery that is slightly used and measures 9.01 vdc, as R.G. says, close enough for our purposes. For purposes of illustration I have the battery in the PNP orientation and the meter leads in the NPN. It works like a charm and has been a time saver.






Roly

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Re: R.G.'s germanium tester
« Reply #1 on: August 07, 2012, 10:38:55 AM »
If you say theory and practice don't agree you haven't applied enough theory.