Neat!
NOS germanium transistors are still highly sought after(and therefore expensive) for music gear such as guitar distortion pedals and pre-amps. They impart a lovely ‘gooey’ quality that modern transistors just can’t do.
NOS germanium transistors are still highly sought after(and therefore expensive) for music gear such as guitar distortion pedals and pre-amps. They impart a lovely ‘gooey’ quality that modern transistors just can’t do.
For non-distorted applications if you do overdrive a bit it can be a lot less harsh too.
Also very difficult to make two the same, so specs were wide and top parts were hand selected from large batches of on-spec parts.
One of my best sources of tasty germaniums was from boards about the same vintage as these IBMs.
I think it's good to make musical or audio circuits from just about any tube or transistor whether it was originally intended for audio or not.
A very simple 2-transistor PCB can have art where it can mirrored and used for NPN or PNP, with positive or negative ground to your battery clip.
I like transistor sockets like there were on some of the early solid-state scientific instruments. Before they could be sure the transistors were more reliable than the sockets.
Put on adjustable bias and find some superb high-performance small-signal BJT silicons for reference. Leave one in then audition the germaniums in the other socket, biasing each one accordingly.
Without a guitar pedal enclosure you can just cut a long guitar cable in half and solder it to the PCB's input & output with the battery hanging off. If the situation arises the whole thing could then be heat-shrunk right there into the middle of the cable. Don't ask me how I know. The python that swallowed an alligator. Doesn't matter if it's positive or negative ground since it's floating.
One megohm impedance for guitar input is good, and play it by ear for a wide choice of output impedance into the guitar amplifier.
I guess I kind of like playing a fuzzy guitar as much as ZZTop :)
Been known to make a pedal or two.
Outside their operating point is another story. As said elsewhere, Ge has a smaller and less sharp drop than Si, which is worlds different for all sorts of clipping distortion applications. The classic example is the Fuzz Face, where the gentler clip made for a warmer sound. Think early Hendrix versus late Hendrix. But the transistors were so inconsistent and the circuit so sensitive to the gain that only one in fifty would sound good!
My understanding though is that it is something you can tune by adding biasing diodes but requires matching.
I am not an expert...just something I remembered from school :)
https://en.wikipedia.org/wiki/Crossover_distortion
Edit: added Vbe
From an engineering perspective, guitar tube amplifiers are horrible at fidelity. But in terms of accurately reproducing what 1950s rock-and-roll sounded like live, they're ideal.
Not super-scientific but good fun.
https://www.analogman.com/fuzzface.htm
http://www.geofex.com/article_folders/fuzzface/fftech.htm
Another one
https://jacquespedals.com/the-ac128-transistor/
An excerpt:
"EPILOGUE : When supply will dry…
In a very close future, all stocks, including mine, of original germanium AC128 or any usable germanium transistor will dry.
Forever.
After this extinction, that only a few aficionados will notice, there will be no other possiblities to obtain THE original fuzz tone than a used Germanium fuzz box or a digital model."
About the AC128, I stopped using it in pedals years ago. It was an ordinary low cost part that later became famous for being used in the original fuzz pedal; as a result it is today sold at outrageous prices, while any normal Ge transistor would work with no difference in sound. It's not the part number, it's the technology: Ge transistors are slower (as in narrower bandwidth) and their sound is therefore less harsh, warmer than Si ones. A pair of ultra cheap ACY* SFT* or many russian ones (less prone to leaks due both to higher [military] standards and their relatively shorter age as the soviets kept producing them long after the west stopped) would sound equally great once the circuit is being adjusted for bias and gain.