
Binary Adder Tube for High-Speed Computers (1955) [pdf] - userbinator
http://www.philbrickarchive.org/adder.pdf
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kens
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...](http://www.bitsavers.org/pdf/univOfIllinoisUrbana/ordvac/ORDVAC_Manual_Volume_1_1952.pdf)
[2]
[http://www.bitsavers.org/pdf/univOfIllinoisUrbana/ordvac/ORD...](http://www.bitsavers.org/pdf/univOfIllinoisUrbana/ordvac/ORDVAC_Manual_Volume_2_Circuit_and_Logical_Diagrams_1952.pdf)

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kragen
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?

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kens
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.

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kragen
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.

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

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Stratoscope
Somewhat reminiscent of that is the Korg Nutube:

[https://korgnutube.com/](https://korgnutube.com/)

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

[https://web.archive.org/web/20190109044731/http://www.ericbr...](https://web.archive.org/web/20190109044731/http://www.ericbrasseur.org/intvac.html)

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

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kragen
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-...](http://www.fundinguniverse.com/company-histories/the-eureka-
company-history/) — 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.

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

[https://www.radiomuseum.org/dsp_hersteller_detail.cfm?Compan...](https://www.radiomuseum.org/dsp_hersteller_detail.cfm?Company_id=2955)

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.

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kragen
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.

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

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lxe
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...

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kragen
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](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.

