Still in an intense ham radio frame of mind, Linux is waiting…

I have spent a surprisingly large amount of time trying to figure out the physical layout for point to point wiring of my tube transmitter. Deciding where the holes went was only the first step — then I had to figure out placement for the terminal strips that would hold internal components, and the wiring runs between them. I decided that I was going to try to lay out the circuits in sections, and build and test them one section at a time. This is a time-honored technique used in many ham radio kits, and one I have adopted for my scratch-building activities. It even resonates with the modular approach one takes to building software.

I also knew that I wanted to color code the wiring to some degree, and save a copy of the schematic highlighted with the color coding, so that when I look at the guts of this thing down the road I have a better chance of remembering what I did. This approach of precise documentation is probably not as imperative for a simple transmitter than it would be for a complex receiver (or a Perl script to make the software analogy) but it seemed to enhance the build experience for me.

Starting with pencil and graph paper, I tried to lay out the physical circuits and the interconnecting wires, making liberal use of terminal strips. I went through many sheets of paper, and several iterations until finally coming up with a layout for each section of the circuit. At one point I even cut out bits from one page and taped them to another, when I realized that a terminal strip was locate in the wrong spot on the original drawing. Here’s an example of what I worked from:

One of many wiring sketches.

With the paper layouts in hand, I started to build. This part was more fluid, more like what I was used to working with Manhattan style. For each block of components, I would mount them on the terminal strip before installing it into the chassis. Then locating where the strip should be mounted, I’d drill a hole, mount the strip, and then run the wiring from the new components to their already installed mates. This approach allowed the production of very dense component wiring on the terminal strips, more so than if I had installed the strips first, then tried to maneuver the soldering gun within the confines of the chassis.

Soldering gun… that was another difference with this project. I have done most of my building before this project using a Weller thermostatically controlled pencil iron, with a very fine tip. This project caused me to pull out the old Weller soldering guns. The 125 watt gun was okay, but actually I got the best results with the 250 watt behemoth that I formerly used only for attaching PL-259 connectors to large diameter coax.

The Behemoth

Here is a slide show that tries to show the organic nature of this kind of building. Unfortunately I did not get the idea of photographing my progress until the power supply section was built, so the first state shows the built and tested high voltage supply and filament wiring.

73,
de N2HTT