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Restoration of a PDR-43 radiac meter?

  1. Oct 29, 2011 #1
    hello. i found a pdr-43 radiac meter at my local ham radio swapmeet today. the device looks like this: http://www.civildefensemuseum.com/southrad/im125dpdr43.html

    as a just for fun project, i would like to attempt to make it functional. right now the unit powers on but adjusting the check meter between beta and gamma does not do anything and the roentgen meter reads a 500roentgen/hr immediately upon powering up.

    i dont know much of anything about radiation or radiation detection but i am a ham radio operating and am fairly comfortable with electronics design. any help or resources would be great.
  2. jcsd
  3. Oct 29, 2011 #2


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    Hi ssbothwell.
    Was there not a probe associated with the device?
    Many of these hand held meters had a plug to fit the actual probe, with the mica window for the geiger-mueller tube that serves as the sensor.
    I have to say that the captions on the link you provide are not encouraging, as the unit has been 'stripped of the check source and some tubes'.
    You need the check source to calibrate the meter and tubes missing sounds ungood. However, there is no obvious empty socket.
    Maybe google the device number and see what turns up.
    Good luck!
    Last edited: Oct 29, 2011
  4. Oct 29, 2011 #3
    there is no socket or anything that a probe might plug into.

    i dont see any spots that obviously used to have components other than perhaps the highlighted points in this image: http://i.imgur.com/fxhbo.jpg

    those things look like clips but they might not be. perhaps they held the 'check source'?

    i'm not sure exactly how these meters work. is the 'check source' a radioactive sample that is compared against the environment for determining radiation levels?
  5. Oct 30, 2011 #4


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    The check source is exactly that, a known source that allows the meter to be properly calibrated.
    The items you identify do sort of look like they might serve as clips to hold a probe, but it seems unlikely the probe would be clipped to the motherboard when the device is built into a robust hand held casing.
    It may be that the greenish plastic surrounds the mica window for the sensor tube, but if so there should be a window on the casing, else the device would be shielded from what it is trying to read.
    Try this site: http://www.civildefensemuseum.com/southrad/im125bpdr43.html
    You were entirely right that the clips hold something, the GM tubes most likely.
  6. Oct 30, 2011 #5
    the pdr-43b in that photo has a slightly different board layout but clearly those things i highlighted are the same clips.

    what do you think the likelihood of finding those tubes and a check source would be?

    maybe i should just be satisfied with the device in its current state.
  7. Oct 30, 2011 #6


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    Finding replacement tubes should be feasible, there is a fair amount of data on the device on the web, including part numbers.
    A check source is more difficult, they are still sold with geiger counters, but those are currently available after a long lead time and at fancy prices. EBay may be a better bet.
    As is, the device is entirely unfunctional. It is too light to work as a doorstop, but would work as a paperweight.

    It is always a bit depressing to have a piece of gear that no longer works. Sort of a standing reproach.
    If you have the needed tools, you could build in an iPhone and use it as a communicator.
  8. Oct 30, 2011 #7
    haha, i would rather keep it as is then install an iphone in it. its a nice relic as is but it would be really amazing to get it functional. maybe i'll get lucky and find a check source and tubes, but until then its just gonna sit on a shelf.
  9. Oct 31, 2011 #8


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    I have a similar gamma survey meter (CDV-715) that has the same problem, it pegs out when on. I'm pretty sure that is a sign that the ion chamber has lost its gas or has otherwise malfunctioned. I don't think there is any way to fix it without getting a new ion chamber.
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