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.
Yep, I have a diy fuzz effect pedal around here somewhere that uses a matched pair of germanium transistors. An older electrical engineer gave me a box of them after I explained how sought after they were. He couldn't get his head around the idea that I would want to use them in a new project when new silicon transistors would be superior for many reasons.
I would say they are like tubes because the distortion is more interesting than the silicon alternatives.
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 :)
Depends on the use. For low distortion, tubes fare better because their operating point is more linear than any single transistor. Ge doesn't make a huge difference here iirc.
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!
Tubes are better since they have amplify with less "zero point crossover distortion". Silicon has .7v and Germanium has .3v Vbe so that is why people seek them.
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 :)
Crossover distortion is completely inaudible if the amplifier is correctly biased as it amounts to a fraction of a fraction percent of the output power, like attempting to listen to a distorted 100 mW pocket radio put on top of a perfectly linear 500W amplifier set at maximum output.
The difference between germanium and silicon transistors lays in the former having much narrower bandwidth, so that it naturally and more gracefully limits higher audio frequencies, and some the artifacts of distortion become less audible making the sound more warm.
Tubes are better than both in this context because they saturate in a really graceful way and produce mostly even harmonics which give tube guitar amps their unique different sound; this is something hardly reproducible in solid state, unless DSPs are involved.
I wouldn't however use tubes for clean HiFi amplifiers as more modern technologies such as Class D today made possible building incredibly good amplifiers at a fraction of the cost, space and energy requirements.
They can also be used for guitars, but as Class D stages distortion sounds like pure junk, everything has to be redesigned so that the final stages are kept clean and distortion happens before entering them.
The distortion introduced by particular electronics is considered an inherent part of the instrument's musical quality by some musicians. Swapping out a high fidelity modern class D amplifier for an old tube amp is kind of like putting steel strings on a classic guitar or violin, instead of catgut or at least a modern plastic meant to emulate catgut. The instrument would never have sounded that brilliant to the musician who wrote a piece before steel strings were introduced.
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.
Semi-related, Brian Wampler made this[1] video where he tries a bunch of different opamps and diodes in some overdrive/distortion circuits, including some germanium and various colored LEDs for good measure.
Glad to see other people that enjoy building guitar pedals. That seems increasingly rare. There are some interesting read if you like electronics and guitars:
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."
A problem with germanium transistors is their tendency to degrade over time until they either start leaking too much current also when unbiased or go directly to short circuit, no matter if they're used or not, so it's advisable to test a small stock before buying bigger lots that could contain many now defective parts. Speaking from experience as I had to ditch like 25% of a big lot purchased years ago in which many were shorted to death.
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.
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.