UK Shipping included; overseas buyers see important note below*

Here's a rare opportunity to own a classic British-made Geiger counter. Mini Instruments models 5.10 and 5.40 have been a popular choice in education, industry and research for several decades and we now have new stocks available for personal users. The two models were produced from the late 1980s to the mid 90s. Although they have been around for a few years they have proved to be extremely reliable and continue to work as well as they did when they were made. There is no reason to suppose why they shouldn't continue to do so for many years to come. They have been extensively refurbished and updated by anythingradioactive, to the point where they now compare very favourably, and even exceed the performance, durability, refinement and ease of use of many modern instruments.

                                          First time buyer?  Please Click HERE

The key feature, still used on current Mini-Instruments (now Thermo Scientific) products, is a large and very easy to read moving coil meter, with a clever logarithmic scale. In a nutshell this means there is no need for a range switch and it can accurately display (in counts per second or cps) both high and low level readings (from normal background, to ‘get the hell out of there’…). Other highlights include:
  • Internal speaker (with mute switch)
  • LED ‘event’ flasher (most models)
  • Audio output socket
  • DC supply socket
  • Detachable probe
  • Adjustable HV supply (approx 250 - 700 volts & 300 - 1200 volts depending on model)
  • Battery Check function
  • Sturdy, compact metal case with carry handle and probe cradle
  • Convenient ‘curly’ probe cable lead
  • Portable operation with long battery life
  • Calibrated prior to dispatch
  • Operating Manual with calibration info and circuit diagram (generic)

As far as performance, reliability and ease of use are concerned the two models are almost identical. The only significant difference is that the Type 5.10's probe supply is adjustable from 250 to 750 volts whilst the 5.40 goes from 330 to 1200 volts. Additionally some units have slightly smaller cases with rounded edges (the others have square edges). They were originally configured to use hard-wired detection probes but their readily adjustable high voltage (HV) circuitry means that they can be used with a wide range of detection devices. This includes standard Geiger Müller (GM) tubes, 'pancake' type GM probes and even advanced Scintillation probes. The result is a highly versatile instrument, capable of functioning in a wide variety of specialist and non-specialist applications and environments (For advanced users the operating manual includes full details of how to carry out HV adjustments).
Refurbishment begins with a complete strip down. The cases are taken back to bare metal, primed and re-sprayed using top quality paint to give them a fresh new look**. Incidentally, we can also apply custom colours and finishes - details on request.
A small number of units in our inventory were originally supplied to the UK's Atomic Weapons Establishment  (AWE), which carried out a number of modifications. They included adapting the power supply for bench operation, adding an external HV output control and fitting a probe connector. Following decommissioning from the AWE we have either removed or adapted the mods. All units now function as fully portable instruments, powered by internal battery pack(s) requiring 8 or 12 standard 1.5 volt AA cells. The 5.10 and 5.40 continues to be an effective bench instrument as we’ve fitted a socket for a standard mains adaptor. Obsolete PTE 100 probe connectors have been replaced with modern TNC connectors. We’ve also installed or re-purposed an LED indicator as an event 'flasher'. All models also have an audio output socket (standard 3.5mm jack), so they can be used with headphones, connected to an amplifier, or a PC, for data logging or analysis.

After reassembly each unit is extensively tested (not a single failure or return so far!), the HV is adjusted and the unit pulse-calibrated – the latter is re-checked immediately prior to shipping.
Currently we are offering these units with a choice of probes (other types are available, or you can choose to use your own probe, just ask...). Instruments with supplied probes are set to the correct output voltage. Please note that some probes are in very short supply, so order early. The standard offerings, which you can select from the Option check boxes when ordering are:

AR-SBT-11: 32 x 18mm mica-window pancake type Geiger Müller detector, sensitive to Alpha, Beta and Gamma radiation (model no 51-SBT-R1)

AR-ZP1400: 16mm dia. mica window GM tube, sensitive to Alpha, Beta, Gamma & X-Ray radiation. (model nos 51-ZP14-R1, 51-ZP14-R2/2,  51-ZP14-S1 &  51-ZP14-S1/2)
AR-SBM-20: thin-walled Geiger Müller tube, sensitive to low levels of Alpha, Beta, Gamma & X-Ray radiation (model nos 51-SBM2-R1, 51-SBM2-R1/2, 51-SBM2-S1  & 51-SBM2-S1/2)


AR-GWG: factory original glass encapsulated Geiger Müller tube, sensitive to Beta, Gamma & X-Ray radiation. (model no 51-GWG S1)

AR-42B: factory original scintillation probe, high Gamma & X-Ray sensitivity (model no 54-42B-L1)

Also available Mini Instruments Type G & Type EL15 probes, custom GM and Scintillator. Details on request.  


Meter Display:                           Logarithmic scale, 0-2000 counts per second (cps)
Audio:                                        Internal speaker, switchable mute
Visual Display:                          LED 'event' flasher
Power Requirements.               8 02 12 1.5-volt AA cells or external 12 - 18 VDC
Current consumption:              1-3 mA (depending on activity)
Battery Life:                               Typical 300 hours (approx. 4-6 hours use per day)
Connections:                             Probe: TNC male; Audio: 3.5mm mono jack socket: External power: 2.1mm DC socket, centre pin positive
Weight:                                       1.6kg (inc. batts)
Dimensions:                              155 x 112 x 105 (& 165 x 115 x 155mm

*Very Important Stuff For Overseas Buyers:
The prices shown are for UK buyers and inclusive of delivery to mainland UK addresses. Overseas buyers should contact us before ordering for shipping options, which vary according to location. Please also note that this item may be prohibited or restricted in some countries.

** Please note that these units may have been in service for several years so there might be some slight marking (scuffs, small scratches, etc.) on the meter face. There may be other cosmetic blemishes, however these are generally minor in nature. 

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Mini Instruments Type 5.10 and 5.40 Geiger Counters

  • Product Code: Mini Instruments Type 5.10 and 5.40 Geiger Counters
  • Availability: In Stock
  • £0.00

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