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Binary Adder Tube for High-Speed Computers (1955) [pdf] (philbrickarchive.org)
29 points by userbinator 15 days ago | hide | past | web | favorite | 20 comments

Von Neumann's popular IAS computer design (ILLIAC, JOHNNIAC, ORACLE, etc.) used an unusual analog adder design. It added two bits and carry-in as analog voltages, and then converted the resulting voltage to digital sum and carry bits. (Don't confuse this with an analog computer.) This seems convoluted to me, but apparently it was a viable alternative to a normal adder based on Boolean logic.

Edit: If you want full details on this adder, pages 60-63 of the manual [1] explains how the adder sums the voltages, getting 54V, 104V, 154V, or 204V from the sum. The digit resolver then turns this voltage into a sum bit. (The carry bit is easier, as it can be generated by a threshold.) You can look at the schematics [2] if you like vacuum tubes; the digit resolver is schematic #200.

[1] http://www.bitsavers.org/pdf/univOfIllinoisUrbana/ordvac/ORD... [2] http://www.bitsavers.org/pdf/univOfIllinoisUrbana/ordvac/ORD...

It's just surprising they stopped at 3 bits. Weren't those parallel machines? I wonder why they didn't go for 5, 7, or 9. Too many comparators in the ADC? I suppose it was too early to use Gray's 10-bit(?) single-tube ADC—if it ever even saw mass production?

This took the place of a full adder, which has three input bits. (In other words, it was a single adder with three inputs, not a 3-bit-wide adder.) I don't see how 5 bits would help.

A carry in, two bits from each addend, and three bits out. Halves your carry-chain length in a ripple adder, and the DAC and adder parts of the circuit are a doddle; even an R–2R DAC is plenty, even at many MHz. But then you need a 3-bit ADC for the output. They didn't know about lookahead carry yet, did they? As I said below, the Chinese abacus uses it, but the relevance of that may not have been apparent at the time.

Integrated Vacuum Tube (IVT) could have been a thing... http://www.ericbrasseur.org/intvac.html

Somewhat reminiscent of that is the Korg Nutube:


Also for anyone who has trouble accessing the page you linked:


Ironically, I got an error on the web.archive.org link but the other one worked just fine.

Toward the very end of the vacuum tube era, there were some "almost solid-state" tubes created, and mainly only used on televisions. You could find old TVs that had parts which were transistorized, and others that had these "tubes". Except they didn't quite look like tubes:


They were almost the size of then-contemporary transistors; just a tad larger. They were made in a special process (inside a vacuum chamber). Pretty much the zenith of the technology, and showed what it could be pushed to do.

I'm getting a "502 Bad Gateway" error

Interesting. A couple of comments:

• at 10 watts it uses several times as much power as my computer.

• what company is this National Union Electric Corporation? Apparently a HVAC company that merged with Eureka in 1959 and is now part of Electrolux: http://www.fundinguniverse.com/company-histories/the-eureka-... — how the mighty have fallen.

• You can hook up the same tube as an oscillator, a flip-flop, an XOR (“inhibitor”) gate, a 3-input AND, or an adder!

• it runs on 300 volts—not a TV flyback voltage but enough to give you a good strong jolt. Electronics has calmed down a lot since the wild 1950s.

• no numbers are given for price or reliability. I assume reliability would improve by reducing the number of tube filaments in your device.

• 300 nanosecond carry delay! That's pretty fast for 1950s logic! I wonder if it was that fast as a flip-flop, too.

History of the manufacturer National Union Radio Corp.; Orange (NJ)


Not only an adder, you could probably mix audio channels and create interesting effects.

In the Space Age, building 300VDC power supplies was basically a prerequisite for any teenage electronics hobbyist.

The BG2 tube was probably not mass produced.

This looks like a design that NU made prototyes of and was willing to manufacture if enough interest developed.

Aha, I see National Union Electric Corporation is the same company as National Union Radio Corporation, having changed its name in 1954, five years before the Eureka merger. Thanks!

You'd probably need feedback to mix audio channels with it, since it wasn't designed to be linear.

It runs on 300 Volts likely from a supply that can source a couple of Amps. I'd rather take the flyback transformer, it will zap you but the voltage will collapse nicely. That 300V is there to stay.

But it's DC, so it feels more like 150 VAC. Hope your hands are dry. Hey, did you fill that due diligence position at your fund?

> Hey, did you fill that due diligence position at your fund?

The response was nothing short of amazing, 30+ people responded, about half we made deals with an several of those are now regulars. Way beyond anything I imagined.

Oh, that's wonderful! Now I really wish I'd responded—at the time I thought it sounded like too much of a commitment. I hope things go really well there!

Vacuum tubes are high voltage low current devices, since they operate by electrostatic principles.

For anyone finding this interesting, I'd also recommend Ben Eaters build-your-own-computer tutorials on YouTube.

I'm curious, what other binary adder designs are out there? This adder-stage-chain design seems ubiquitous. I wonder if anything else can be done considering the current state of technology... or just for fun, like analog circuits or no clock, etc...

Carry-save adders (as used in Chinese 7-bead abacus) avoid the ripple-carry penalty mentioned in this article, as does the bit-serial design it mentions. Residue number systems are another option to limit carry chain length, which additionally save you loads on multipliers: https://web.stanford.edu/class/ee486/doc/chap2.pdf

When you don't need to add, just count and compare, you can use a LFSR, as the Atari video generator infamously did for sprite positions.

Modern computers, even back to the 1970s, usually instead use lookahead carry to get logarithmic carry delays instead of linear ones.

If you use a compound or otherwise non-binary base, carry logic is different, but the same basic options still exist. The 8008, 8080, 8086, i386, and amd64 instruction sets have “auxiliary carry” bits for use with BCD arithmetic; a separate DAA instruction adjusts the binary addition result to be a BCD result. The weirdest thing is that the 8086 added DAS, DAM (?), and AAA.

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