Germanium transistors: logic circuits in the IBM 1401 computer
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[1]: https://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.52...
Even "depleted" uranium is somewhat radioactive, and it's a toxic heavy metal.
To be fair, I think the sharp chunks of metal and plastic would kill you before the heavy-metal poisoning could.
Now there's a sentence that I never thought I'd write.
- Difficulty growing high quality crystals
- All the process chemistry for building devices would be different
- Toxicity/radioactivity
The third one is IMO the least important. There are a lot of semiconductor materials that theoretically have properties comparable to or better than silicon for solar cells (as this paper suggests). But having a theoretically good band gap doesn't matter if the actual material as grown is full of deleterious defects. We're really good at growing near-perfect silicon crystals. We're not so good at growing perfect crystals of iron (II) sulfide, uranium dioxide, etc.
Even if that could be solved, re-developing all the chemistry and tooling for fabricating dense logic/memory devices based on uranium dioxide instead of silicon would require an extraordinary investment of money and time. It could be comparable to or even more expensive than the transition to extreme ultraviolet lithography.
And it can take kilos of 99 percent pure raw material to end up with a few grams of 99.999 or better.
Silicon was already available in rail cars having 99+ percent purity for steelmaking.
What a wealth of material you have on righto.com!
Blown away.
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.
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
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!
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.
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.
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.
So in things like amplifiers it gives you less zero point crossover distortion. In digital I believe it lends to a faster switch time but I could be very wrong on this part.
Germanium is much more rare so the cost is naturally higher...from what I know.
I can't imagine a logic circuit of that era that was technically capable of being clocked at 100Mhz, 30 years before these frequencies became the norm.
Based on the speed, it's plausible that it is a type of ECL, but I don't know where the diodes would fit in. IBM had other names such as current-steering logic for ECL.
Keep in mind that the 10ns speed doesn't mean you can run at 100 Mhz, since there are likely to be multiple levels of logic, as well as other delays. But it's still pretty fast.
I understand that transistors amplify current but how do they amplify voltage (like in CMOS)? Isn't voltage going to amplify current also?
I never understood this.
In a bipolar (NPN or PNP) transistor, the current through the base causes a larger current through the collector, amplifying by the beta factor. So the transistor is amplifying current. But the current depends on the voltage between the base and emitter, so from that perspective the voltage controls the transistor too.
Whether you're amplifying current or voltage depends on the circuit, so I can't give more than a handwaving answer.
In field effect transistor (in which the actual physics involved are at least for me simpler to grasp) the gate is isolated from everything else and voltage at the base directly changes the geometry of the conductive channel between the S and D pins. In effect the gate voltage directly influences the resistance of the component. MOS is an name for particular practical realization of this mental model.
In bipolar junction transistor (ie. PNP/NPN) there are two diodes that are positioned just so that conduction of one of them influences the other in such a way that when one is positively biased the other will conduct even when reverse biased. For the typical BJT these two diodes have significantly different construction and thus there is difference between emittor and collector, but the effect works both ways (and in fact many circuits will somewhat work even with the 2N3904 connected the wrong way around). The effect is also caused by change of properties of doped semiconductor material in response to electric field gradient but (at least for me) there is no directly applicable model involving discrete lumped components changing their parameters in response to external stimuli that matches the underlying physical principle.
Your DC battery or power supply provides your headroom, and the transistor Base or Gate senses a small increment of that voltage and can sometimes deliver as much current as it takes to push the voltage across a resistance or impedance right up to the rails.
Any voltage through a resistor will produce a current, and any current through a resistor will produce a voltage. By properly connecting resistors at the transistor base and collector, one can turn a driving voltage into a current and the collector current back into an output voltage. The basic common emitter transistor amplifier circuit is a good example as it shows how a current amplifier like a transistor is used to amplify a voltage. Resistors are the secret that allow all permutations: voltage to voltage, current to voltage, voltage to current, current to current.
In BJT transistors the "control stimulus" is the current flowing through the base pin, while for (MOS)FET transistors it's a voltage potential between the gate and source pins.
The amplification happens because in the right region the change in effective resistance is high for small variations in the "control stimulus".
If you drive a BJT with a resistor in front of the base pin, you can drive it with a voltage. If you put a resistor between the gate and source pins, you can drive a MOSFET with a current source.
So the way you control them is different, but what they end up doing is the same. And by using a resistor you can effectively change the way you drive them.
Of course, some times this is easy, and some times it is hard. Once you find the bad card, the restoration team likes to fix the bad card rather than just replace it. This can have its own challenges. I spent a long time trying to fix a card from the printer that ended up having a cracked trace that was intermittently bad. All the signals looked good, yet the card didn't work.
For a detailed look at a problem, I wrote a blog post about a core memory problem that turned out to be an inductor that failed open. After fixing that, the computer wouldn't power on. We replaced some weak transistors in the power supply, but that didn't help. Finally we found an undocumented fuse that had blown, probably from one of the boards we swapped. Replacing that got everything running again.
http://www.righto.com/2017/12/repairing-1960s-mainframe-fixi...
Anyway, thank you for those detailed information on the article.
It reminds me of how NASA simply lost so much of the original media, and what he have today is either purely accidental or the result of a considerable amount of work done by volunteer restoration groups. We really need to get a grip on this problem now, and it would be nice if IBM would actually help out with that - instead of leaving it to volunteers.