| T O P I C R E V I E W |
| nonus |
Posted - 06/06/2024 : 10:14:47
Hello. I recently purchased a GMC-500+. The M4011 tube broke upon delivery.
 
I decided to replace the tube with an analogue one. I found SBM 20-1 at my local market. This tube is almost the same size as the M4011, but soldering is required.
I want to share the solution on how I replaced the M4011 tube with SBM 20-1. The main problem with fastening to the terminals is the lack of insulators at the ends of the tube. I made my insulators on a 3D printer.
It looks like it's working. I don’t know how to calibrate a new tube, I set the voltage of tube No. 1 to 400 V, dead time to 190 µs. Radiation source smoke detector.
.stl file: https://drive.google.com/drive/folders/1L16OdlTfxJCyQSkh4ATgTmpHkmbiccOs?usp=sharing |
| 4 L A T E S T R E P L I E S (Newest First) |
| nonus |
Posted - 08/03/2024 : 22:38:40
I think the sbt-20 is a more sensitive tube, so switching to the m4011 will be a downgrade. Also, if you have a connector for connecting external tubes, replacing the first tube inside loses its relevance. |
| Kaninbjerget |
Posted - 08/02/2024 : 08:58:09
Sorry for a little late answer.
Not an expert on tubes but I don't think resistor really matters that much - and it's still well above the minimum value. As for calibration you'll need to find out what it's sensivity for Cs-137 is as that's what generally used in GQ's geiger counters - and the other tube in the counter is also set for by factory default.
Otherwise M4011, J305 (~88-90 mm version) and J321 are all equivalents so any of those can go with factory default settings. Probably you cn't find a black tube but you can wrap it in non shrinked thin black heatshrink like it's done in most recent revisions of the 300 series.
The J321 / J305 / M4011 are readily available on Ali Express etc. and it's not going to break the bank. |
| nonus |
Posted - 06/12/2024 : 04:53:05
The voltage of SBM-20-1 is the same 400 V as SBM-20. Perhaps I need to change the resistor on tube 1, the SBM-20 has a recommended resistor of 5.1 MOhm. For the M4011 tube, a 3.1 MOhm resistor is used, in the SBM-20 datasheet the minimum resistor value is 1 MOhm. Overall it works well, even if there is some measurement error. I'm interested in trying other tubes. I ordered the SBT-10 tube. If I connect the sbt-10 to the gmc-500+ instead of the si3bg, will it work? I can reduce the number of anodes to 5 pieces if the gmc-500+ has a current limitation. The SBT-10 tube is highly sensitive, so it will be useful for checking food.
https://istok2.com/data/3019/ |
| EmfDev |
Posted - 06/11/2024 : 15:14:23
Looks like the SBM-1 has higher CPM reading with the smoke detector compared to the M4011. Not sure about the calibration though. Check the tube datasheet for voltage. |
