What can you do with a leaky germanium transistor?
Leaky germaniums are all too common and if you select the good devices from a bag of transistors, you will have a pile of rejects that are not suitable for fuzz or booster circuits. What can you do with them?
You can use them as diodes. The base-emitter junction will have a forward voltage drop of about 0.25v and can be used as a clipper in a fuzz circuit.
Also, even though the transistor may have too much b-e current leakage for use in many circuits, it can still probably be used as a buffer. The basic circuit is shown at the start of this article and it can be built on stripboard using the same layout as for the jfet buffer that I published previously. The transistor pin configuration is different for the germaniums so you will have to match the leads to the proper pads.
Also, an AC128 or similar transistor will require a positive ground, so the battery power connections will have to be reversed. The black battery lead will go to the top row of connections on the stripboard and the red battery lead goes to the Gnd pad.
If you want to increase the input impedance of the Ge buffer, change the values of R2 and R3 to 470k.
I breadboarded this circuit last night using an AC128 with 700uA of leakage current and got good performance. A 2.5v pk-pk triangle wave was passed by the buffer with no visible distortion on the oscilloscope display.
You could even parallel Ge buffers as I did with the jfets, and make a germanium buffer/splitter!
Here is a sample stripboard layout for the buffer:
This circuit can also be built on the AMZ Multi-Purpose PCB.