50W QRP Amplifier – 3D Printed Case Design and Livestream

With the 50W QRP amplifier project coming along nicely, I felt it was time to start thinking about a reproducible case for the project. And for custom, reproducible cases, 3D printing is my current tool of choice.

I ended up designing the case on a YouTube Livestream on Saturday night, to which a few great colleagues stopped by to ask questions and offer advice. The full video is below.

The case is in two parts – a box with standoffs for the PCB and holes for connectors, and a lid with labels. The standoffs and the attachment holes for the lid are meant to connect with M3 threaded-inserts and be held down with M3 machine screws.

This was my first time using Fusion 360’s Eagle Sync function – since Eagle was acquired by AutoDesk in 2016, it makes sense that they’ve been working to integrate PCB design workflows into their other products. The sync was fair straightforward – open Fusion360, select Eagle Sync, select your board file in Eagle, and after a minute or two of importing, up pops your PCB in Fusion360. Neat! I’m still struggling with how to handle board cutouts in eagle, and I’m not sure how well they’ll be supported in Fusion, but that’s a project for another day.

Here’s the final design as it turned out in Fusion360:

The PowerPole model was provided by Chris Wych, a theatrical propmaster who’s done some really interesting work with Fusion360, including using it to model some 2d-printable geodesic designs which then folded up into geometric shapes. Very cool!

First print of this design coming soon!

73

This post is cross-posted to my more general-purpose nerdery blog, jeff.glass/blog.

50W QRP Amplifier – Schematic, PCB ver 1

The 5W-to-50W QRP HF Amplifier project is rolling along nicely  – I received the first PCB draft in the male this week and am 90% of the way through assembling it, with only heatsink-placement left to sort out.

I’ve made a couple of additions to the schematic since the original layout, including a relay-activated indicator (R27 and its LED) and an RF-output sensing LED (from C14 to its associated LED to ground) along the the lines of VK3YE’s recent project. There’s also a space on the PCB now for a low pass filter with the same footprint as Hans Summers’ LPFs over at QRP-Labs. Not that you’d necessarily want to reuse a QRP LPF for a 50W amp, you’d be in danger of putting too much voltage on the caps, but that would be a simple change.

Here’s the schematic as it exists now:

 

And here’s the current boards (layout, unpopulated, populated):

I’ve already got a little laundry list of things to modify for a second rev of this board, including, in no particular order:

• Swap the Diode placements the vertical to preserve board space
• Add footprints for alternate relay packages
• Add footprints for alternate trim-pot packages
• Re-think component designators for clarity
• Add bypass jumpers for the 3dB input pad and the LPF.
• For some reason, the none of the component values printed on the silkscreen, will need to sort that out
• I’m not sure if I screwed up how to designate a cutout or if JLCPCB doesn’t do them for its bare-bones PCB service, but I’d like not to do the next set with a drill press and a nibbler.

Hoping to put this on the air soon for some signal tests. Hear you there!

73

This post is cross-posted to my more general-purpose nerdery blog, jeff.glass/blog.