Today Karen and I replaced the PMT and base assembly on LNCU3 and the
base on LNCU4. As the new (i.e. out of the box) base was too long for the
NC PVC housing, we swapped the 'posts' which form the axial structure of
the base, with those from an older base (which measured OL resistance at
the HV terminal and did not work.) That base will go to Mario for repair
along with another which measured an overload resistance (SHV R s/b ~
13-16 MOhms). With a good signal on LNCU3 and 4 I proceeded to gain match
them with 3 Sr-90 sources using LNCU5 as a benchmark. After ballparking
the voltage with the scope and then fine tuning with the DAQ I believe
that the proper voltages for the new setup should be:
LNCU3: -2675V
LNCU4: -2675V
(see plot below)
NOTE that these tubes are now drawing a lot of current (about 1.6 mA a
piece) this is in comparision to the 1.1 - 1.5 mA of the other NC tubes.
Pete
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Pete Karpius
Graduate Research Assistant
Nuclear Physics Group
University of New Hampshire
phone: (603)978-6152
FAX: (603)862-2998
email: karpiusp@einstein.unh.edu
http://pubpages.unh.edu/~pkarpius/homepage.htm
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