MSTR-4 MCTP-4 Alpha-Beta-Gamma geiger tube

This is a cool tube! The MSTR-4 is a mica end-window all glass geiger tube. Is so rare to find out there but once you can find one the problem is shipping, is so fragile! Is extremly sensible, the seller told me that it’s natural background is 25000CPM!!! I need to test it but… the trouble that it need 1200V to operate. Some photo and info sight down there on the page.

  • Working Voltage 1200V – 1350V
  • Plateau Length 200V Plateau Slope 5% / 100V
  • Inherent counter background (cps) 25 000 Pulses/min   !!!!!!
  • Interelectrode Capacitance 25pF
  • Load Resistance 8 – 15 MOhms
  • Working Temperature Range +5 +35 С
  • Length 180 mm
  • Diameter 35 mm
The MSTR-4 geiger tube with it’s datasheet
MSTR-4 view from back

Take care about the round electrodes. They could easily be detached from the glass if handled roughly. Don’t try to solder on it contacts or the glass will break. Use round clip from a PCB fuse holder.

MSTR-4 mica window

The mica window makes this tube to be very sensible. It can detect weak alpha rays too!

Stay tuned, I’ll try to feed his 1.2Kv needs and make a video of it @ work.

SI-22G CИ-22Г Geiger Muller tube

This tube is highly sensitive, similar to the STS-6, ideal to make a natural background monitoring equipment. It could be used also to make a personal dosimeter but it’s size is a limiting factor.

SI-22G tube

It’s characteristics:

  • Working Voltage: 360 – 440V
  • Initial Voltage: 285 – 335V
  • Recommended Operating Voltage: 400V
  • Plateau Length: 100V
  • Plateau Slope: 0.125% / 1V
  • Inherent counter background (cps): 1.16 Pulses/s
  • Cobalt-60 Pulse Gamma Sensitivity: 540 pulse/uR
  • Load Resistance: 9 – 13 MOhms
  • Working Temperature Range: -50 to +70С
  • Length: 220mm
  • Diameter: 19mm

SI3BG CИ-3БГ Geiger Muller Tube

I’ve bought this tube some time ago with other tubes from an ukrainian seller because of it’s price. Usualy it is sold at 2€ each. This tube is so small and cute but is… absolutely useless.

SI3BG russian geiger tube

If you try to measure the natural radioactivity or if you try to test barely radioactive samples like pechblende or uranium glass you’ll obtain CPM in the range of 4-5 for the natural background and 15-20 for a medium active pechblende sample.

Typical application circuit

It was made to test fallout from a nuclear explosion. I’ve seen is usen in russian personal counters to help other two SBM20 tubes when the situation is too hot. Practically, is just usefull for pocket counters/alarms for soldiers during a nuclear war.


Homebrew a Geiger rate meter

Hi! In order to count pulses generated from Geiger tube when striked by a ray, we need a counter. If we combine a pulse counter with an high voltage supply for the Geiger tube, we have made a rate meter.

This is my inplementation:

Homebrew rate meter for geiger tube

On the left there is the power on/off switch and the BNC female connector where you connect the Geiger probe. In the center the 16×2 LCD display shows on the top line the result Counts Per Minute (CPM) of the… last minute. On the lower left there is a 60 second countdown to show how much time remain to update the CPM line. On the lower right there are the total pulses counted from the last 60 second countdown. It reset each 60 seconds. On the front panel, top right, you can see the voltage selector (400/1000V) to power the tube. The 1Kv position is for photomultiplier tube. The “pulse” RCA connector is used to send the tube pulses, amplified, to a PC soundcard or other devices for future use.

HV main board lower side
HV power supply plus linear regulators and pulse amplifier










The HV section is very simple, a single transistor oscillator that drive a CFL lamp transformer from an old LCD display. The rectified output is leveled by a series of zener diodes and filtered by a C-R-C-R-C network of 10nF@2Kv rating blue disk cap. and 1Mohm 1/4W tru-hole resistor.

HV power supply schematic, CRC filter omitted. 5V supply filter omitted too…

The output noise is down below 4mVpp at 1000V!!! with 80-100Megaohm load. The pulse amplifier is used to reverse the pulse polarity from negative to positive, enlarge it and drive the counter circuit. I’ve copyied it from the Theremino website at the section  Theremino PMT

Pulse amplifier adapted trom Theremino PMT

The counter, finaly, was made by an Arduino nano that drives the LCD and count the pulses incoming on the interrupt pin D2 on the falling side of the pulse. The source code is splitted in various images.

Library initialization, pin definitions
Global variables, custom characters definition
countPulse interupt funcion
Timers and display.

STS-6 CTC-6 Geiger Muller Tube

Hi! I’ve just received two STS-6 Geiger Muller tubes from Ukraine. They are HUGE! Their size is 199mm long X 22mm diameter. In this video that I’ve made you can see I’ve enclosed in into a thick walled Alluminium pipe so I can filter out all beta’s and count just gamma’s. This because without it, my pechblende sample count more than 14500 CPM at 2cm from the probe. Uranium decay emit alpha + a lot of beta BUT…some of his impurities (radium) decay with gamma. I’m interested in gamma emitting sources.

The Uranium decay

This is the video:

And some more info about the tube and pics:


  • Working Voltage 390 – 400V
  • Initial Voltage 285 – 335V
  • Plateau Length 80V Plateau Slope 0.125% / 1V
  • Inherent counter background (cps) 1.83 Pulses/s
  • Interelectrode Capacitance 10pF
  • Load Resistance 5 – 10 MOhms
  • Working Temperature Range -500 +700 С
  • Length 199 mm
  • Diameter 22 mm
The STS-6 tube with it’s original box and datasheet. The screwdriver is for size comparison
This tube is so BIG!

Tube amplifier with EL84 push-pull stereo

Hi! In the mid of year 2016 I’ve made this project: a stereo amplifier to improve my TV audio You know, LCD TV’s speakers are so… @#[]! I’ve choosed to use a classical vacuum tube design: a push pull of EL84 tubes drived by ECC82. Output 12W of power per channel.

12W seems not too much but… hey! I can guarantee that my 60 sqm living room are very well sonorized with half of that power.

EL84 Push pull <– Here you can download the zip file with PCB’s ready to print, schematics…

The schematic is very accademic, nothing unusual for this type of amplifier.

Schematic of the amplifier

As you can see into the next photo, this design is very well know into the literature and online with few little differences like a negative feedback loop (that I have not included) and on driver tube.

Another classical design 90% identical to mine

The first section of the ECC82 amplify the incoming signal to drive, the second section. Now it generate an identical but 180° shifted signal on it’s chatode to drive the EL84 tubes in push-pull mode class AB. The tubes are connected in ultralinear mode because avoiding the global negative-feedback loop, I still need some form of feedback in it. Solved using an audio output transformer designed to operate in ultralinear mode. It is a 8k plate-to-plate handmade by me. Take a look at this extract from EL84’s datasheet. The ultralinear mode have such low distortion at full power!!!

EL84 push-pull comparison chart

I ve choosed the ultralinear tap at 43%. If you know how to made such type of transformer you know what I’m talking about… if not, please buy one ready made from Hammond, they have good value for the price. this is just a suggestion.

The transformer make 90% of the quality of the amplifier because it characterize heavily the sound.

The power supply is straightforward:

Power supply schematic

It separate the power supply from the left and right preamplifier/driver tubes, into the schematic they are marked X1-X2. The double CLC filtering drop down at the right level the ripple.

X4, the power output is just two positive contacts for the 300V one for the left and one for the right output power transformer. The ground is taken by the X1-X2 ground and then there is no need for another one ground (and the PA-tranny doesn’t need gnd).

Each PA transformer is made by 4000+4000 turns of Ø0.14mm CuEn (copper enameled) wire. The secondary winding is 4+4 ohm so 75+75 windings of Ø0.8mm CuEn. The magnetic core is a EI96/80 column size is 32x32mm weight is 1.7Kg each.

The power supply transformer is a 250V @ 200mA plus 3,15-0-3,15 @ 5A The filament winding (3,15-0-3,15) is a bit unusual because I prefer to balance the filaments current grounding the center-winding-tap to the methal chassis of the amplifier. With this trick I can reduce the 50Hz hum made by filament at infinitesimal level.

This power transformer is made by a primary winding of 826 turns of Ø0.4mm CuEn wire (in Italy mains are 230Vca). The high voltage secondary winding is 987 turns of Ø0.25mm CuEn and the low voltage winding for the filament supply is 25 turns of Ø1.4mm CuEn. The core is a EI96/80 column size still remain 32x32mm same weight of the audio transformers.

In total 5.2Kg of iron and copper 🙂

I’ve made some PCB for this project