Dual Mode, Analog/Photon Counting Photomultiplier Detection System

For spectroscopy and microscopy experiments in the UV/Vis/NIR region of the spectrum, a photomultiplier tube (PMT) is the ideal detector for quantitative low light level measurements. A PMT is extremely sensitive, with very wide dynamic range so it can also measure high levels of light. PMT’s are also very fast so rapid changes in optical signals can be reliably monitored. As a practical matter, PMTs are durable, long-lived, and economical.

Optical Building Blocks provides a simple, self contained PMT housing that operates in either analog or photon counting modes with the flick of a switch. This ambient PMT housing is ideal for standard side-on PMTs that are used from 185 to 900 nanometers. It has a very low dark count for a non-cooled PMT housing providing a dark count of only ~ 50 to 500 counts per second (cps) depending on the PMT selected.


Key Benefits

  • Compact Size
  • Inexpensive
  • Operates in Analog or Photon Counting Modes
  • Detection from 185 to 900 nm
  • Complete Package
  • LCD display of output signal
  • Easy to Use

PMT's are better than photodiodes and APD's for low light detection

Although the quantum efficiency (QE) of a PMT is less than that of a silicon photodiode or avalanche photodiode (APD), a PMT has a much lower limit of low light detection due to the high current amplification (~ 107) of the electron multiplier in the PMT. It is because of this large gain and low noise that a PMT provides significantly better low light sensitivity than a photodiode or APD.

Looking for NIR Detection?

For NIR detection beyond 900 nm please take a look at our CoolOne cooled PMT housing for photomultiplier detection from 185 to 1,200 nm and also our InGaAs detectors for detection from 0.8 to 1.9 μm.

The OBB ambient PMT housing includes the following

  • On/off switch
  • Complete analog and photon counting circuitry
  • Analog or photon counting mode/output switch
  • Line voltage power supply
  • High voltage power supply
  • LCD display of PMT high voltage or measured analog signal
  • Signal out BNC connection
  • High voltage adjustment knob
  • External high voltage control input BNC connection (for optional external control)
  • RF shielded case
  • Internal socket for most 1 1/8-inch side-on photomultiplier tubes

OBB’s photomultiplier detection system is very convenient and easy to use. It is built as a complete unit using modern design techniques and components. Everything needed to quantitate the intensity of light is packaged into a compact, attractive housing that attaches conveniently to your experiment. There are no unsightly boxes for power supplies or a multitude of cables tangled on your bench-top. The system incorporates a high voltage supply, all detector electronics, and the controls in a compact, attractive housing that also contains the PMT. You have a choice of standard PMTs to choose from or you can select from any other 1 1/8-inch side-on photomultiplier tubes that operate from -200 to -1,100 Volts DC. The PMT high voltage is shown on a digital display on the housing or you can select to show the actual analog signal from the PMT with just a flip of a switch. The high voltage can be adjusting manually or controlled externally with a signal at the “External Voltage Control” BNC. Power is delivered from an external AC adapter that is included.



All controls and displays are available on the front and side of the OBB PMT housing.

Control Specifications

Dual Mode, Analog/Photon Counting Photomultiplier Detection System


LCD display of high voltage or signal


On/Off switch
Analog/Digital Mode switch
Voltage/Signal Display switch
Voltage Adjust potentiometer
Analog Gain selection
Analog Time Constant selection
Analog Offset

BNC Connectors

Signal Out
External Voltage Control


Physical Specifications

Dimensions (WxDxH) 4 x 4 x 8 inches  
Weight 4 lbs  

High Voltage Power Supply Specifications

Input ± 15 VDC, 250 mA  
High Voltage -200 to -1,100 VDC manually adjustable LCD displays actual cathode voltage  
External High 0 to +5 VDC (0 = -200 V, 5 = -1,100 V)  
Voltage Adjust Continuously adjustable  
Input Regulation ± 0.05% max. (for 15 V ± 1 V input).  
Load Regulation ± 0.05% max.  
Ripple 100 mV p-p max.  
Temperature Coefficient ± 0.01% max. (+5 to 40°C)  
Drift ± 0.03%/hr. max. (after 15 minute warm-up)  

Analog Mode Specifications

Gain Settings: 1 µA = 1 V
0.1 µA = 1 V
0.01 µA = 1 V
0.001 µA = 1 V
Time Constant Settings:
(with Corresponding Analog Frequency)
0.05 msec (20 KHz)
0.5 msec (2 KHz)
5 msec (200 Hz)
50 msec (20 Hz)
500 msec (2 Hz)
Offset Correction: ± 50 nA  
Signal Output on BNC connector: Analog voltage  

Photon Counting Mode Specifications

Linear Dynamic Range: 5 orders of magnitude*  
Dead Time: 250 ns  
Signal Output on BNC connector: TTL  

* Linear dynamic range of the OBB photon counting PMT housing. The intensities were produced by attenuating the fluorescence emission of a fluorescein sample with neutral density filters.

The back of the OBB PMT housing has a ¾ inch opening which exposes the PMT photocathode. There are four mounting holes for M3 flathead screws.

Compatible Optical Building Blocks


OBB has an excellent 200 mm focal length monochromator that would allow you to use the OBB PMT housing as a scanning and tunable light detector. If you would like to couple the PMT housing to our monochromator, then we have a micrometer slit adapter to physically connect them and create a tunable detector with variable bandwidth selection. To learn more about our monochromators, click here.

Sample Compartment

If you would like to couple your PMT housing to a sample compartment for spectroscopy measurements of solutions or solids, then we have an ideal solution. The OBB QuadraCentric sample compartment is an excellent unit that has various sample handling capabilities. You can connect the PMT housing and then have up to three other input or output optical channels to or from the central sample holder. So you could create a right angle fluorometer or scatter system, a transient absorption system or a straight through absorbance spectrometer with the appropriate electro-optical components. For each optical channel in the sample compartment there are collection optics and a filter holder for wavelength selection. To learn more click here.

Light Guides

Liquid light guides, fiber bundles and single fibers are excellent light delivery components that offer flexibility and versatility. OBB Corporation has a selection of light guides to choose from, as well as SMA adapters for single fibers. If you would like to use a liquid light guide, fiber bundle or single fiber with your OBB PMT housing then we have a number of light guides and adapters to choose from.

Optical Choppers

If you would like to use the OBB PMT housing in analog mode with a lock-in amplifier for noise reduction, then we have  then we have an optical chopper with a USB interface that can do the job. It is used on a stand-alone basis with a third party lock-in amplifier. To learn more click here.

Other Accessories

Micrometer slit accessory

This allows you to continuously adjust a slit mounted in front of the PMT housing to attenuate the light delivered to the detector.