A Vacuum Tube Single Board 1-Bit Computer [video]
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What's the memory? It ought to be a delay line, for traditional reasons.
It's hard to find non-IC delay lines today. "Analog" delay lines in guitar pedals now use a charge-coupled bucket brigade IC. They're analog in amplitude, but discrete in time. I was expecting that someone would still be manufacturing some kind of acoustic delay line product, but there's not much out there.
The EDSAC rebuild people built a delay line memory.[1] Not too complicated, but a pain to get it to work.
You need a piezoelectric or magnetostrictive transducer driving a metal rod, with a receiving sensor at the other end. Liquid level sensors which work that way are common. A metal rod dips into the liquid, and a transducer at the top sends a ping down the rod. The impedance change where the rod enters the liquid causes a reflection, which is sensed by the transducer that sent the pulse. Converting one of those into a delay line might be possible.
You need some length. The speed of sound in steel is around 5,000 meters per second, so you'll need 5 meters for a millisecond delay. This can be a coil; it doesn't have to be straight. A longer delay line can store more bits, but the cycle time is slower.
These things are temperature sensitive, so they either have to be self-clocking or temperature controlled.
Another interesting option (for ROM) is core rope memory. CuriousMarc has the ultimate explanation: https://www.youtube.com/watch?v=hckwxq8rnr0
> at the speeds they are targeting, I think delay lines might be difficult
Speed of the torsional wave is around 3000-3500m/s depending on the alloy you use. You can make the coil about several dozen meters long before running into issues (practical torsion wire delay lines were 20 to 80m long). That would give 6 to 27ms of delay, which can keep 600 to 2700 bits in the loop at 100kHz, or 10 times more at 1MHz. The same amount of cores would be far more labor intensive to make.
There is no RAM, just a single 1 bit accumulator. It's made of vacuum tubes configured as NOR gates.
Also, maybe: build some op-amp analog adders, multipliers, and wire them into a digital computer via ADCs and DACs for your math functions. (Could also do log, antilog, maybe other functions as well.)
Do you really need pentodes at the speeds involved? It looks like the guy is toggling a switch by hand to generate a clock signal. Pentodes are devices for RF amplification.
Those 6AU6 tubes are 7 pin units, but they contain only one pentode element. Two pins for the heater, then five pins to hook up the pentode.
There exist common 8 or 9 pin tubes that contain two triodes, with which you could cut the tube count in half. (You wouldn't save any money because those tubes cost about twice as much. But less board area and fewer tube sockets counts for something.
About why to use tubes? I don't know, entertainment purpuoses I guess. His ventures into computing using tubes entertain some at least[0].
[0](n=1)
I'm planning on building a stereo Mullard 5-10 next year, I know it will be objectively worse than a modern HiFi amp or even a more recent valve-based design at actually being an audio amplifier but I think it would be a fun anachronism to use a homebuilt 1950s amp with modern equipment and there's a lot to be said for the aesthetics of valve amps as well.
What's the concern with using tubes? Do you really need tubes for guitar distortion?
He's also done quite a few videos restoring old vacuum tube based test equipment from like HP. He does some really cool work.
Technically no. But most professional guitarists still swear by tube driven amps. Solid state is getting better every day, but I think we're still a long way out before most guitar players give up their tube amps.
I am perfectly happy with my Line6 Helix, but a few friends still turn their noses up at it.
Tubes are still the reference model.
All the DSP cores in a modern amp are just a cover band playing tube tones.
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1. I mean other than digital solid-state getting more highly integrated and faster, to run more complex software. The necessary analog audio paths in a DSP system aren't getting better.
It’s more “tube virtualization” is getting better every day.
Reliability/longevity, power draw/dissipation, high or higher voltages.
(Speaking of the latter, I wonder what plate voltages the guy is using. I'm guessing it could be well below 100V.)
Most guitar amps in what sense? Most guitar amp units shipped? Probably the biggest volume there is amateurs.
> recreate some sounds from the 40s-60s.
Try 40s-90s-00s--...?
Tubes are commonly used right for tones right up to the heaviest metal. It's common for some solid state driving device to be used, like an overdrive pedal. That doesn't necessarily provide any needed gain, but rather shapes the clean tone, which has an effect on what kind of distortion you get.
(Ironically, one difference between "old school" metal and "modern" metal that amps used in modern metal have more tubes: like three 12AX7's in the preamp rather than two. Nothing needs another vacuum tube more than "modern"!)
In other words, the use of tubes in rock guitar continued to evolve well into the 1990s. So tubes are the key to authentically reproducing the sounds heard in 90s and later metal, not just 40s through 60s.
Which is not to deny that solid state devices aren't used for distortion, either as driving elements for tubes or alone.
I prefer to have solid state almost everything, including the power amp; but there should be a couple of tubes in there for making noise.
- You've not gotten away from hardware; it's still there.
- You're using billions of transistors to simulate the operation of dozens of transistors/tubes, which is inelegant. The chip with those transistors may be small, much smaller than your project, but, in theory, your design with the few dozen transistors could be shrunken down to a chip that would be barely visible to the naked eye.
The educational value of building hardware is obvious to me; it cannot be replaced with simulation, and simulation runs on hardware that someone built, who knew how.
Why even bother building something when you can simulate it on your PC in 10th of the time?