May 27, 2026
Hot tubes, wild side quests
Dimensions of the Geiger-Muller Tube Holder on the GGreg20_V3 Geiger Counter PCB
Tiny tube measurements sparked big maker energy and a sudden urge to chase cosmic rays
TLDR: The company published exact fit details for the glass tube used on its radiation counter board so buyers can choose compatible parts without guesswork. The community response skipped straight to maker fever, with one commenter joking that the post revived plans for a cosmic-ray tracking build.
A seemingly modest update about how big a radiation-sensing glass tube can be on the GGreg20_V3 board somehow turned into classic maker-community chaos: one part practical shopping guide, one part “you’ve activated my next weird project.” The company behind the board explained that people kept asking which replacement tube sizes actually fit, especially because the older Soviet-era option became hard to find and newer Chinese-made versions can vary a little. So they posted drawings, photos, and a plain-English attempt to stop buyers from ending up with a tube that’s just a bit too long.
And then the comments immediately did what comments do best: skip past the dry measurements and turn the whole thing into a vibe. The loudest reaction came from user magicalhippo, who basically said this innocent sizing note had reignited their urge to build a cosmic ray hodoscope — a device for tracking particles from space. In other words: readers saw “tube holder dimensions” and heard “permission to start an absurdly ambitious science side quest.” That’s the real mood here.
There wasn’t much outright fighting, but there was a deliciously familiar maker hot take bubbling under the surface: no detail is too small when your whole project can fail over a few millimeters. The joke writes itself — this is hardware drama at its purest. One team is just trying not to buy the wrong part; the other is already halfway to building a home lab because a sizing chart gave them ideas.
Key Points
- •The article provides additional PCB tube-holder dimensions for the GGreg20_V3 Geiger counter module beyond what is listed in the datasheet.
- •The guidance is intended for customers who buy the GGreg20_V3 without a tube and need to source a compatible Geiger-Muller tube independently.
- •The GGreg20_V3 was originally designed for the SBM20 tube, and that tube still fits the module.
- •IoT-devices adopted the J305 as a replacement after SBM20 stock became unavailable, but notes that J305 tubes on the Chinese market can vary in dimensions.
- •The article includes supplier-based J305 dimensional data, a technical drawing, and photos, and reports only a small number of defective or out-of-spec J305 tubes over several years.