Subject: 5B07-0 and 5B04-0 PMTs opened today
Ioanni.Katsavounidis@lngs.infn.it
Date: Thu Feb 10 2000 - 10:55:26 EST
Ciao a tutti,
Today we worked on 2 PMTs that had problems:
- 5B07-0 ("very bright, one of the 2 tubes had double gain")
- 4B05-0 ("4B05-01 has lost gain from -4mV/spe to -2mV/spe in 2 months")
The counters were turned OFF between runs 19077/19078 and initially
5B07-00 (= ser. # 7273, the tube that had this strange "double gain")
got changed with a spare (= ser. # 7174), together with all 4 PMT HV bases
for 5B07-00,5B07-01,4B05-00,4B05-11. Checking the PMT gain under the new
configuration, we found big differences in HVs for these tubes.
Thus, we decided to swap tubes, including one of the spares as follows:
WAS -> IS
===================================
spare(1) (= ser. # 7431) -> 5B07-01
5B07-01 (= ser. # 7500) -> 4B05-01
4B05-01 (= ser. # 7420) -> spare(2).
In the final configuration, here are the HVs/base resistances:
PMT ser. # HV R(base) Splitter resistance
-----------------------------------------------------
5B07-00 7174 -1620V 9.4Mohm
5B07-01 7431 -1605V 9.4Mohm 89Kohm (installed 98K)
-----------------------------------------------------
4B05-00 6755 -1455V 9.3Mohm
4B05-01 7500 -1410V 9.4Mohm 300Kohm (installed 294K)
-----------------------------------------------------
PMT paper logbooks have been updated and tankend operation checklists
compiled and archived in the appropriate place.
5B07 and 4B05 will be put back in ACQ at the next run change
(19079/19080).
A presto,
Ioannis
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