Germanium transistor tester questions

[Bret608]

Hi all,

I am in the process of building the following GE transistor test circuit (thanks again for the vero, Josh!):

http://tagboardeffects.blogspot.com/2012/08/germanium-transistor-tester.html

I have a question or two--is this essentially doing the same job as the Small Bear test circuit? Could the SB circuit be built on this layout, and if so, what to do about the 2.49k resistor?

Just wondering--the SB circuit seems a bit simpler and easier to use, but honestly I could go either way.

Thanks!

Bret

[muehring]

I'm not familiar with the small bear test circuit.  Maybe post a link.  I recently built the geofex tester you mentioned and I recommend checking out this thread on byoc http://www.buildyourownclone.com/board/viewtopic.php?f=9&t=38231&p=327228&hilit=germanium+tester#p327228
Duhvoodooman has a gain calculator on there that helps if you don't have perfectly matched resistors and battery.

[Bret608]

Hey,

Here is the Small Bear version:

https://www.smallbearelec.com/HowTos/FuzzFaceFAQ/FFFAQ.htm

Actually though, thanks for pointing out the spreadsheet from BYOC! I was having trouble finding those exact values in the electronics lab where I work, hence my liking the simple 1m arrangement. I'll look again and see if I can find anything close to RG's values. It's good to know the formula works even if you're not 100% on with the resistor values.

One more question, this time about powering the test circuit. Would it be possible to power it off of my circuit testing rig, which has alligator clips for power and ground, instead of a battery?

[muehring]

Using the testing rig to power it should be fine if it's 9v.  Just measure the voltage it's supplying and put it in the spreadsheet if you use it.

[Bret608]

Thanks!  That makes sense to put it in the spreadsheet as I know it's putting out something like 8.96 volts.

Can I use it that way to test both PNP and NPN, as long as I reverse the power and ground from the test rig and the DMM leads as appropriate?