21 Dec
2025
21 Dec
'25
5:16 p.m.
So Santa had his sleigh out for some test drives tonight. For
ballast (the real gifts won't be loaded until Wed night), he used
a big stack of engineering drawings from the 1940s. Fortunately
for us, his "spirited" driving included one turn that was too
tight and out flew the drawings, where they landed on my lap. For
anyone who's as eager as I am to geek out over 1940s computer
design, I share them with you here:
http://cs.drexel.edu/~bls96/eniac/drawings/
There are over 900 drawings in the set. Most of these images come
from scans of microfilm taken of the patent trial exhibits. There
are also about 100 copies that the Smithsonian had imaged and put
up on their web site. I've processed them all to approximate
something like we remember from our technical drawing classes in
college (well those of us old enough to have taken them). The
quality varies widely, but a large subset are readable down to
the measurements for the panels and the component values in the
circuits.
If you've read Kathy Kleiman's excellent book (Proving Ground)
about the original ENIAC programmers, you may have found yourself
wondering what the block diagrams from which they figured out how
to program the machine looked like. Well, those are among the
drawings here. So feel free to try your hand at figuing out how
to program it from them.
One subset of the drawings is conspicuous by its absence, the
PX-15 series. From what I can tell, those were drawings of a
delay line memory unit that was never built. Those drawings were
not part of the trial exhibits and were not microfilmed. However,
some physical copies do exist, and I am hoping to get back into
the archives to scan them at some point in the future.
Beyond that, there are a number of drawing numbers that are
skipped, and I suspect that these are drawings that do (or did)
exist, but were not microfilmed for whatever reason. So if anyone
has or comes across any drawings that are not on this list, or
better copies of those that are, feel free to send scans my way.
For anyone wanting to grab copies of the full set, it should be
pretty easy to extract a file name list from the index.html file.
I'll leave the sed command for extracting the list as an exercise
for the reader.
For printing, all of them are sized in the PDF files for 8.5x11
or 11x17 paper. Be warned, printing all of them without duplexing
and folding the 11x17s to fit into a normal binder, ends up
filling 2 4-inch binders.
By the way, if anyone has access to the adapter shown in drawing
PX-4-119, I think there's an error in the drawing and I'd like to
check to see if either there really is or if I'm missing
something.
Thanks and have fun,
BLS
21 Dec
21 Dec
8:07 p.m.
On 2025-12-21 6:16 p.m., Brian L. Stuart via cctalk wrote:
So Santa had his sleigh out for some test drives
tonight. For
ballast (the real gifts won't be loaded until Wed night), he used
a big stack of engineering drawings from the 1940s. Fortunately
for us, his "spirited" driving included one turn that was too
tight and out flew the drawings, where they landed on my lap.
Well this is not the first mishap,remember the movie "Santa Claus
Conquers the Martians"
For
anyone who's as eager as I am to geek out over
1940s computer
design, I share them with you here:
http://cs.drexel.edu/~bls96/eniac/drawings/
That was the first computer I knew of was from the 1950's Book of knowledge.
There are over 900 drawings in the set. Most of these
images come
from scans of microfilm taken of the patent trial exhibits. There
are also about 100 copies that the Smithsonian had imaged and put
up on their web site. I've processed them all to approximate
something like we remember from our technical drawing classes in
college (well those of us old enough to have taken them). The
quality varies widely, but a large subset are readable down to
the measurements for the panels and the component values in the
circuits.
If you've read Kathy Kleiman's excellent book (Proving Ground)
about the original ENIAC programmers, you may have found yourself
wondering what the block diagrams from which they figured out how
to program the machine looked like. Well, those are among the
drawings here. So feel free to try your hand at figuing out how
to program it from them.
One subset of the drawings is conspicuous by its absence, the
PX-15 series. From what I can tell, those were drawings of a
delay line memory unit that was never built. Those drawings were
not part of the trial exhibits and were not microfilmed. However,
some physical copies do exist, and I am hoping to get back into
the archives to scan them at some point in the future.
Beyond that, there are a number of drawing numbers that are
skipped, and I suspect that these are drawings that do (or did)
exist, but were not microfilmed for whatever reason. So if anyone
has or comes across any drawings that are not on this list, or
better copies of those that are, feel free to send scans my way.
For anyone wanting to grab copies of the full set, it should be
pretty easy to extract a file name list from the index.html file.
I'll leave the sed command for extracting the list as an exercise
for the reader.
For printing, all of them are sized in the PDF files for 8.5x11
or 11x17 paper. Be warned, printing all of them without duplexing
and folding the 11x17s to fit into a normal binder, ends up
filling 2 4-inch binders.
By the way, if anyone has access to the adapter shown in drawing
PX-4-119, I think there's an error in the drawing and I'd like to
check to see if either there really is or if I'm missing
something.
Thanks and have fun,
BLS
To help with the programming.
https://www.cs.drexel.edu/~bls96/eniac/simulator.html
Ben.
23 Dec
23 Dec
4:16 p.m.
On Sun, Dec 21, 2025 at 09:07:03PM -0700, ben via cctalk wrote:
Well this is not the first mishap,remember the movie
"Santa Claus Conquers
the Martians"
I haven't thought about that movie in years. What a classic.
To help with the programming.
https://www.cs.drexel.edu/~bls96/eniac/simulator.html
I really need to update that page too, and I promise someday
I will get around to adding the modifications that were made
to the machine over its life. I've also had some requests
that I add some more substantive interactivity.
Now where is that time turner I asked Santa for?
BLS
5:39 p.m.
On 2025-12-23 5:16 p.m., Brian L. Stuart via cctalk wrote:
On Sun, Dec 21, 2025 at 09:07:03PM -0700, ben via
cctalk wrote:
Do you have a good introduction on how to program that thing?
Well this is not the first mishap,remember the
movie "Santa Claus Conquers
the Martians"
I haven't thought about that movie in years. What a classic.
To help with the programming.
https://www.cs.drexel.edu/~bls96/eniac/simulator.html
I really need to update that page too, and I promise someday
I will get around to adding the modifications that were made
to the machine over its life. I've also had some requests
that I add some more substantive interactivity. Now where is that time turner I asked Santa for?
Back in 1955.
BLS
Ben.
8:35 p.m.
On Tue, Dec 23, 2025 at 06:39:03PM -0700, ben via cctalk wrote:
When Back to the Future came out in 1985, 1955, 30 years earlier,
seemed like such ancient history. And now it's been 40 years
since then. I'm too young to be this old.
BLS
On 2025-12-23 5:16 p.m., Brian L. Stuart via cctalk
wrote:
Not as good as I would like. This paper:
https://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=8467000
goes through a pretty simple programming problem and develops
the programming on the ENIAC to solve it on the simulator,
but that's about the extent of anything I've done yet along
those lines.
At one of the VCFs this year, I was talking with some people
about further developing the interactivity of the simulator
and the idea came up to create a video or other online experience
that walks the user through a simple calculation. So at least
a better form of introduction is on my list. When is another
question entirely.
On Sun, Dec 21, 2025 at 09:07:03PM -0700, ben via
cctalk wrote:
Do you have a good introduction on how to program that thing? To help with the programming.
https://www.cs.drexel.edu/~bls96/eniac/simulator.html
I really need to update that page too, and I promise someday
I will get around to adding the modifications that were made
to the machine over its life. I've also had some requests
that I add some more substantive interactivity. Now where is
that time turner I asked Santa for?
Back in 1955. 
22 Dec
22 Dec
10:42 a.m.
On Dec 21, 2025, at 8:16 PM, Brian L. Stuart via
cctalk <cctalk(a)classiccmp.org> wrote:
So Santa had his sleigh out for some test drives tonight. For
ballast (the real gifts won't be loaded until Wed night), he used
a big stack of engineering drawings from the 1940s. Fortunately
for us, his "spirited" driving included one turn that was too
tight and out flew the drawings, where they landed on my lap. For
anyone who's as eager as I am to geek out over 1940s computer
design, I share them with you here:
http://cs.drexel.edu/~bls96/eniac/drawings/
Wow.
I glanced at a few of them. Was surprised to see an inverter using a 6L6. Then looked a
little further and came across an element that uses an 807.
The 6L6 and even more the 807 are rather substantial power tubes. 807s are commonly seen
in amateur radio transmitters in the 1940s and 1950s, good for 50 watts or so power
output. I have a couple, they are very nice tubes. I don't remember the 6L6 ratings;
20 watts, perhaps? Both are also rather large, the 807 especially, when compared to
typical "receiver" tubes.
paul
23 Dec
23 Dec
7:09 p.m.
On Mon, Dec 22, 2025 at 01:42:54PM -0500, Paul Koning wrote:
I glanced at a few of them. Was surprised to see an
inverter using a 6L6. Then looked a little further and came across an element that uses
an 807.
The 6L6 and even more the 807 are rather substantial power tubes. 807s are commonly seen
in amateur radio transmitters in the 1940s and 1950s, good for 50 watts or so power
output. I have a couple, they are very nice tubes. I don't remember the 6L6 ratings;
20 watts, perhaps? Both are also rather large, the 807 especially, when compared to
typical "receiver" tubes.
Good catch. The majority of the 6L6s are used in parallel pairs in
the circuits identified as "transmitters." They are drivers for
transmission lines that can be up to about 80 feet long with taps
about every foot. The pulses they're transitting are about 2
micro-seconds long. So they really are like small RF transmitters
pushing long transmission lines pretty hard.
When I first saw those designs, I thought in terms of over-design
from the context of TTL signals on busses measured in inches. Then
again, we're talking about a 50 volt swing charging up a big long
coax capacitor. So the more I've dug into it, the more respect I
have for the design. In fact, there are also pulse amplifiers
that can be inserted to bump the signals on long lines.
One of these days, I'm hoping to write all this up into a thorough
technical description of the machine including all the modifications
that were made over its 10 year life. The scary part is that I've
been digging into it for about 10 years now.
BLS
25 Dec
25 Dec
9:58 a.m.
On Dec 23, 2025, at 10:09 PM, Brian L. Stuart
<blstuart(a)bellsouth.net> wrote:
On Mon, Dec 22, 2025 at 01:42:54PM -0500, Paul Koning wrote:
Sure, that makes sense. And there's a fair amount of power involved to produce fast
pulses of significant amplitude.
It reminds me of the CDC 6000 series mainframe console display. That uses what amounts to
oversized oscilloscope tubes -- electrostatic deflection tubes, but 14 inches diameter vs.
the usual 5 inches or so you would find in a typical oscilloscope. We sometimes referred
to them as "radar tubes" but classic radar displays use electromagnetic
deflection (with a rotating yoke).
Since the display rate is pretty fast -- a vector-drawn character takes about 2.5
microseconds, with 100 ns per stroke step -- and the deflection waveforms are at least
several hundred volts, the deflection final stage is a push-pull pair of 3CX100A microwave
transmitter tubes, rated at 100 watts at several hundred MHz. In the DD60 display they
are DC amplifiers, with 2 kV anode voltage. Not the usual environment for a computer
technician to work in.
paul
I glanced at a few of them. Was surprised to see
an inverter using a 6L6. Then looked a little further and came across an element that
uses an 807.
The 6L6 and even more the 807 are rather substantial power tubes. 807s are commonly seen
in amateur radio transmitters in the 1940s and 1950s, good for 50 watts or so power
output. I have a couple, they are very nice tubes. I don't remember the 6L6 ratings;
20 watts, perhaps? Both are also rather large, the 807 especially, when compared to
typical "receiver" tubes.
Good catch. The majority of the 6L6s are used in parallel pairs in
the circuits identified as "transmitters." They are drivers for
transmission lines that can be up to about 80 feet long with taps
about every foot. The pulses they're transitting are about 2
micro-seconds long. So they really are like small RF transmitters
pushing long transmission lines pretty hard.
When I first saw those designs, I thought in terms of over-design
from the context of TTL signals on busses measured in inches. Then
again, we're talking about a 50 volt swing charging up a big long
coax capacitor. So the more I've dug into it, the more respect I
have for the design. In fact, there are also pulse amplifiers
that can be inserted to bump the signals on long lines.
20
days inactive
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days old
7 comments
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