MILSPEC TEARDOWN: CP-142 RANGE COMPUTER
Posted by Jonathan M. McCoy on 16th September 2020

As some of my preceding paintings right here at Hackaday will attest to, I’m a large fan of World War II generation. Something approximately going in with wooden airplanes and leaving with jet combatants and area capable rockets has usually captivated me. So whilst one in all my lovingly crafted eBay alerts changed into precipitated by using something claiming to be a “Navy WWII Range Computer”, it’s safe to mention I changed into interested.

Not to say I had any concept of what the component became, mind you. I only knew it looked vintage and I had to have it. While I eagerly awaited the tool to reach at my doorstep, I attempted to perform a little research on it and got here up pretty a great deal empty-surpassed. As you may think, a whole lot of the technical facts for hardware that changed into developed in the 1940’s hasn’t pretty made it to the Internet. Somebody become selling a technical guide that potentially might have blanketed the feature of this device for $one hundred on another site, but I concept that is probably a chunk immoderate. Besides, where’s the a laugh in that?

I decided to attempt to decipher what this device does through a careful exam of the hardware, consultation of what little technical records I could pull up on its person components, and some modern gear. In the cease I suppose I actually have an awesome idea of how it works, but I’d actually like to pay attention if there’s all of us available who might have in reality labored with hardware like this and could fill in any blanks.

 

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OVERVIEW
The first thing I changed into struck with turned into how large and heavy this aspect is. Compared to modern hardware, the CP-142 is constructed like a literal tank. It’s built of thick folded sheet metal with a captivating crinkle coating of a few kind that simply screams “Old School Military”. It’s roughly the scale and form of a toolbox, with a gap on the bottom that makes me assume it was at the start meant to straddle some different piece of hardware.

Controls are very minimum: there’s an energy switch and “Intensity” dial on the left, and a window to view a mechanical readout on the right which reads “Miles”. On the side of the tool, there’s a 70mm graduated dial which actions the counter when it’s turned around. It’s straight away clean that rotating the dial is supposed to set a selected distance, but more on that later.
After loosening two thumbscrews on the lowest, the CP-142 may be opened up on a hinge to view the internal components. Two truly categorized first-rate adjustment knobs close to the number one manipulate seem to indicate that starting up the hardware to fiddle with the internals was not unusual. There’s even a little hex key stressed to the body of the tool which can be used to loosen or dispose of the control dial, possibly so the operator may want to align the marked graduations with the pointer on the front of the case.

ELECTRONICS SECTION
The left-hand aspect of the CP-142 is dedicated to the electronics, which consists of 4 12UA7 tubes, a 6AK5, a 6AL5, and a Raytheon UX-7350 transformer. There’s no PCB in this tool, all the wiring is executed factor to a point, with a few tough metallic “rails”.

WIRING
A thick package deal of wires comes out of the electronics phase into a bus bar that’s placed right below the lid hinge. There’s also a transfer here which cuts electricity to the device when the lid is opened. Clearly, the device would be opened sufficient that a safety interlock and methods to save you twine fatigue from repeated commencing and remaining become deemed necessary.

The bundle of wire is wrapped up with loops of black thread every 10mm or so, which was in reality achieved via hand. It’s the first rate to feel the connection to the producing staff of the time. In all likelihood, a woman who was a part of the exertions force who stepped as much as help the battle effort turned into tasked with tying those little thread loops round bundles of wires for 8 hours a day along the one’s employees routing the wires and doing the point-to-factor soldering.

Above the bus bar, the wiring goes to the power switch, depth dial, and a bulb which lights the mechanical show. The construction of the transfer is some thing I’ve by no means visible earlier than, as in place of having a Bakelite body as you’d normally anticipate from the technology (and that’s present in different areas of the CP-142), it’s fabricated from sandwiched pieces of some kind of fiberboard.

DIAL ASSEMBLY
Everything in the CP-142 is a fascinating look at how hardware, and in particular navy hardware, turned into designed 70-strange years in the past. But of all of the additives of this gadget, the dial meeting is the most brilliant. It takes input from the person, however additionally presents them with a actual-time display of the range presently selected. This is completed mechanically, with the counter and dial on the same axle.

A pair of beveled gears are used to attach the axle to a huge potentiometer established ninety stages from the dial. Rotational end-stops are provided by a small section of threaded rod and a touch constrained nut that rides it. The nut can not rotate, so it moves horizontally across the rod because the dial is grew to become. Once it hits the minimal or most journey, precisely machined ledges come into contact, making similarly rotation not possible.
Or you enter tool aficionados accessible, I have to mention, the movement of this dial is high-quality. The dial itself weighs in at 260 grams, and even with all of the mechanical movement involved it feels extraordinarily clean. I’ve spent more time than I care to admit spinning this dial to and fro over the last few days.

AWAKENING A SLEEPING GIANT
I’m no longer sure at what factor I determined I desired to try to strength up the CP-142. I kept searching for the purple tag attached to the tool that announces “TESTED OK – 4/6/54” and wondering if a machine that has been in storage for sixty-four years might nonetheless paintings.

None of the wires had been categorized, however documentation for the vacuum tubes turned into easy sufficient to come back by means of (the 12AU7 continues to be utilized in audio amplifiers), and with a multimeter, I should tune where the whole thing turned into going. The bus bar and rigorously coloration-coded wiring also helped immensely. I knew what voltages the vacuum tubes wanted, and on which pins they have to be getting it. In concept, it ought to simply be a be counted of plugging the appropriate voltages into the bus bar and hoping for the exceptional.
I’ll be completely honest, once I saw that show flicker on and people tubes begin warming, up for the primary time in over six many years, it becomes a quite extremely good moment for me. This is the type of era that I’ve always favorite, but to have this legitimate piece of history up and going for walks on my bench gave me a possibility to hook up with that technology that I’ve in no way had earlier than.