If you keep up with various retro vacuum tube projects, you probably have run across [UsagiElectric] aka [David]’s various PCBs that he makes on his own Bridgeport EZ-Track 3-axis milling machine — massively oversized for the job, as he puts it. In a recent video, [David] walks us through the steps of making a sample PCB, introducing the various tools and procedures of his workflow. He points out that these are the tools he uses, but the overall process should be similar no matter what tools you use.
- Logisim to validate logic designs
- TINA-TI, Texas Instrument’s version of the TINA SPICE simulator
- DesignSpark PCB for schematic entry and PCB layout
- FlatCAM, a computer-aided PCB manufacturing tool
For this video, [David] makes a half-adder circuit out of four vacuum tubes plus a seven-segment VFD tube to show the combined sum and carry outputs. Momentary switches are used to generate the two addends. Using this example, he proceeds to design, simulate, build and demonstrate a working circuit board. We like his use of the machined pin socket inserts for building a vacuum tube socket directly into the board.
Now this process isn’t for everyone. First of all, a Bridgeport mill is a pretty good sized, and heavy, tool. That said, these procedures should adapt well to other milling machines and engravers. We should point out that [David] is making boards mostly for vacuum tubes, where circuit trace width and spacing distances are generous. If you’re planning to make home PCBs for a 273-pin PGA chip, this isn’t the technique for you.
It seems that the bulk of [David]’s vacuum tube PCBs are single-sided, and reasonably so. They use wire links here and there to jump over traces. Adapting this process to double-sided PCBs is doable, but more complex. Are you milling double-sided boards in your lab? If so, let us know about it in the comments below.