Fujifilm PMT26A Photomultiplier Tube


The Fujifilm PMT26A photomultiplier tube module came from a teardown. The teardown of a Philips / Fujifilm PCR Eleva S / CR-IR 357 X-ray image scanner for computed radiography, became the basis for this reverse engineering project. You can see the teardown of the entire Fujifilm PCR Eleva S machine here. Teardown of the polygon laser scanner module here.

Computed radiography is based on reusable phosphor imaging plates, instead of film. The x-ray exposed imaging plate is scanned with a red laser timed to a photomultiplier tube. This reads out one single pixel on the imaging plate at a time. The returned light from the scanning laser has a different intensity dependent on the amount of absorbed x-ray energy. The signal from the photomultiplier tube is translated into a 12-bit grey scale resolution image.

This article covers the reverse engineering of the Fujifilm PMT26A PMT module. The module contains the photomultiplier tube, high voltage power supply and analog amplifier.


WARNING!: Working with electricity is dangerous, all information found on my site is for educational purpose and I accept no responsibility for others actions using the information found on this site.

Read this document about safety! http://www.pupman.com/safety.htm

Reverse engineering of Fujifilm PMT26A

It took a great deal of cutting with a new sharp box cutter, to get in-between the acrylic light guide and the blue glass filter window of the photomultiplier tube. It took about 30 minutes to free the two parts from each-other, without harming tube or light guide.

The photomultiplier assembly is mounted on a sheet metal holder with the tube going out through a grounded layer of mu-metal for shielding the tube from electrostatic interference. The PCB has a output amplifier and power supply part on the left side of the socket and a high voltage power supply module on the right side.

The Fujifilm PMT26A board has two connectors, both goes to the SCN23A card in the main computer of the Philips / Fujifilm PCR Eleva S scanner. CN1 is a 34-pin flatband pin header and CN2 is a coaxial output signal from the output amplifier.

Fujifilm PMT26A Power Supplies

The output amplifier is shielded, the differential amplifiers on the board is using +12/-12VDC from a 88M12T and 79M12T regulators. The +15/-15VDC input goes directly to the HV module. The HV module is a YE DHFF-001 from 2008, it does not have any datasheets available online.

From the pin 5 of the YE DHFF-001 comes the negative high voltage supply for the photomultiplier tube. The cathode of the tube is connected to the 4 blue capacitors that is tied to ground, to ensure a stable voltage at the start of the high voltage chain.

As more electrons are accelerated from the first dynode to the next and so on, less current is needed to drive them on, this is done with a pure resistive divider network between the dynodes, but it has its drawbacks with loss of linearity and output deviation in the region of 10-20% at high output current. A improved divider network uses capacitors to insure stable supply voltage at peaks and even individual power supplies for each dynode can be used to do the same.

From the photomultiplier tube handbooks from Hamamatsu, the requirements to a PMT high voltage power supply reveals that quality control is needed to achieve a line/load regulation at +/- 0.2% and ripple noise/temperature drift at 0.05%. The Hamamatsu R6233 photomultiplier tube is a 10-stage 14-pin version that can use up to -1500V dynode supply.

Fujifilm PMT26A Signal Amplifier

The Anode output signal from the Hamamatsu R6233 photomultiplier tube goes to a Analog Devices AD8610. The AD8610 is a precision, very low noise, wide bandwidth, JFET operational amplifier.

The next amplifier IC in the chain, which seems to handle Offset and Gain potentiometers, is the Analog Devices AD744. The AD744 is a precision BiFET operational amplifier.

A sampling IC from Analog Devices ADG417 is placed to the side of the signal chain, indicating that it might have to do with sample and hold, test, calibration or blue LED referencing. The ADG417 is a LC2MOS precision mini-DIP analog switch.

The output amplifier next to the CN2 output coaxial connector is a Analog Devices AD817, which is a high speed, low power, wide supply range amplifier. It can supply a minimum of 50 mA at up to 50 MHz.

Fujifilm PMT26A Schematics

Schematic from the service manual. I marked the needed pins for the module to run without the computer/scanner analog-to-digital conversion modules.

A photomultiplier tube can be a very sensitive instrument, depending on the negative supply voltage for the dynodes. From the PMT handbooks graphs show that common PMT behavior the amplification is highly dependent on the high voltage supply. The -500 VDC this module uses gives a mere amplification of 6.000 times. This level of amplification is sufficient for the computed radiography. For a more interesting task like radiation detection with a scintillation crystal, it is suggested that -1 to -1.2 kV is needed. The R6233 tube should give a amplification of 1.000.000 times and up towards 100.000.000 times, but at the cost of precession.

Cosmic Radiation and Detecting Muons

Cosmic radiation is a result of high energy particles, like protons and atomic nuclei, that moves through space nearly at the speed of light. These can come from our own sun, outside our solar system or from other galaxies. When these particles smash into the atmosphere of Earth, these particles smash into atoms and produces large amounts of pions, muon and neutrinos. The decay chains can be very complex and some of the resulting muons can reach the surface of the earth and be detected with scintillation materials or cloud chambers.

Early measurements of muons at Earths surface, posed a dilemma as the numbers were much higher than calculated. Muon are used as an good example of relativistic time dilation to explain the increased particle range for high energy particles.

Cosmic Radiation illustration by SyntaxError55: https://en.wikipedia.org/wiki/Cosmic_ray#/media/File:Atmospheric_Collision.svg

Experimentation: Getting the unit to run and scintillation plastic for radiation detection

19th October 2023

After having seen the connection diagrams in the manual, I was confident to test the module with power on. I was using a power supply with +15 VDC, -15 VDC and GND. I shielded the window of the PMT with aluminium foil to block out any light. You risk burning holes in the dynodes of photomultiplier tube, if its flooded with light while powered up. Protect and treat your PMT with great care.

Judging from the computer board power supply of +5 VDC for signals. I tried my luck with putting +5 VDC on the input pins I had located. It was also mentioned in the manual that the module has a “high voltage hardware ok” and “high voltage software ok ” signal, that both had to be high for the high voltage to get active. It turns out that the input pin 5, labelled HVSH is “High Voltage Software High”. When +5 VDC is applied to pin 5 the high voltage supply is generating -500 VDC.

The output signal is sine wave like peaks, with different pulse widths, depending on the detected particles.

The following 3 waveforms have a clear muon signature with a steep pulse and a subsequent event of 2/3 energy about 2 to 10 microseconds later. The mean life span for a muon is 2.2 microseconds.

The following 2 waveforms have different levels of energies and over different time frame signatures. So these will remain to be unknown particle interactions.

Demonstration of Fujifilm PMT26A

Teardown, reverse engineering and test of the Fujifilm PMT26A board.


[1] Hamamatsu, “Photomultiplier Tubes – Construction and Operating Characteristics”, January 1998.

[2] Hamamatsu, “Photomultiplier Tubes – Basics and Applications”, Third edition, Handbook, 2006.

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