21 Aug
2008
21 Aug
'08
8:26 p.m.
William Blair wrote:
The other factor ... this was a proof of concept here. OK , it worked
We got our Grant, Fame,PHD what ever and it shelved as it was for
achademic use only.
Like Zuse, and the other computer-calculators of the time had
paractical problems to solve.
The other minor factor ... solid state diodes did not happen untill
about the middle of WWII.
Ben,
> A
multi-stage direct coupled vacuum tube circuit. Fun.
>
Yes, be prepared for some fun, in both senses of
the word: it is fun to play
around with, but the implemention of tube logic can be problematic or
unreliable, at least in the way the ABC tried to implement both NAND and NOR
gates with resistive input circuitry.
Atanasoff makes it sounds easy in his paper, but if one reads it closely
it's not quite so, at least as measured by modern standards where one comes
up with a gate design and then simply repeats it ad infinitum.
After reviewing the ASM circuit on your web page, it became readily apparent to me that
it would likely be a major challenge to fill in the blanks for those missing resistor
values and end up with something that actually worked reliably.
The ABC reconstruction and the original required
(at least some) hand-picked
resistors in the gate circuits.
I bought the excellent book ?The First Computers ? History and Architectures? mainly
because of its content on Konrad Zuse?s relay-based machines. However, in its included
paper on the reproduction of the ABC, the authors state:
?In building add-subtract modules, we found the circuits very demanding of precise
resistor values. We have evidence that Berry hand-selected resistors from bins until he
found ones that worked, and we attempted the same tactic. In measuring the
characteristics of 10% resistors, we discovered the distribution about the nominal value
shown in Fig. 3. (It?s a graph of a bell curve between -10% and 10% with a big notch in
the center of the curve). Apparently, the manufacturer had already segregated the
resistors close to nominal value. Hence, we found it necessary to use 1% tolerance
resistors.?
So, here?s a 14 gate, multistage, direct coupled vacuum tube circuit that apparently
requires various hand-selected values of 1% resistors to work properly. Whew!!! I think
I?m going to start with something a great deal simpler, like a single flip flop or astable
multivibrator using an inexpensive 9-pin miniature dual triode at low voltages to see if I
can even get that to work.