Given germanium transistors of arbitrary specifications, is it generally possible to substitute resistor values to get behavior akin to that with AC128s? I realize that figuring out said values is an exercise all its own, but I wanted to get an idea if it's even approachable. I have a box of 1980s NOS Ge PNPs (all same make and model) that I'd like to be able to make use of; just substituting them into the classic circuit does not produce a usable result.
Thanks!
Thanks!
I assume this should be possible. Ge-Transistor widely differed in cutoff currents and current gain, so this often requires re-calculation of biasing resistors.
It would be helpful if you measure DC-operating points with the original AC128, for instance each collector voltage of any pnp.
Then you replace and adjust biasing resistors to the same voltages.
Anyway a circuit diagram would be helpful.
It would be helpful if you measure DC-operating points with the original AC128, for instance each collector voltage of any pnp.
Then you replace and adjust biasing resistors to the same voltages.
Anyway a circuit diagram would be helpful.
From RG Keen's Geofex site:
The Technology of the Fuzz Face
It covers the circuit but also covers transistor selection. Plus there are changes that can be made to it discussed. Everything you need to know...
If you want to diddle with resistor values, that is why trimmer pots were invented.
The Technology of the Fuzz Face
It covers the circuit but also covers transistor selection. Plus there are changes that can be made to it discussed. Everything you need to know...
If you want to diddle with resistor values, that is why trimmer pots were invented.
Enzo - That's the site I based my own clone on. I used two AC134 transistors I'd been carrying around since the 1970s and it sounded glorious (I later broke one of them running some tests; I replaced it with another vintage Ge PNP I had on hand; I lucked out and it worked fine). I built a little tester based on his circuit and I also built a prototyping box with all the components laid out in Fraunhofer clips and banana jacks at every node. Between that and Qucs on the laptop, I'm about as well set up as I can be to get these transistors to work if I can just put in the effort.
As voltwide mentioned, as long as you are biasing them correctly, not a problem.
There are also some schematics for NPN distortion/ fuzzes around, you can plonk PNP Ge in those as well, just reverse everything with polarity, and bias correctly.
They will sound differently but, cover them in epoxy, slap a sexy name on it, add marketing hyperbole, sell them for >400$ 😀
There are also some schematics for NPN distortion/ fuzzes around, you can plonk PNP Ge in those as well, just reverse everything with polarity, and bias correctly.
They will sound differently but, cover them in epoxy, slap a sexy name on it, add marketing hyperbole, sell them for >400$ 😀
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