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CAUTION : Remember that the High Voltage Circuit Cards operate up to 2000Vdc, and the HV capacitors can retain that charge for a considerable time. Any maintenance should be proceeded by removing the power cord from the AC or DC line. With the unit turned off let 5 minutes elapse until any disassembly occurs. This allows the Preamp's bleeder string to discharge the HV Circuit Card HV Supplies, and the associated capacitors, after which the HV circuit cards may be handled without fear of shock. No maintenance should be done with any input power (AC or DC) connected.
Replacing the Photomultiplier TubeStart with the new tube, and the roll of tape in your hand. With the end half way down the tube and at a 45 degree angle bring it in a gradule arc, up and around the tube, close to the top of the PM face about 1/32", then go down around the tube and using about 1/2" overwrap, wrap the tube towards the base, covering about 1/2" of the base where the base and glass join, and leaving the rest of the base bare. Take the white or black tube protector ring and place it onto the tube. If it fits loose, wrap some tape around the end of the tube to make a slightly snug fit. Then take 8 - 3" strips of tape and place them vertically on the side of the tube protector and down onto the tape on the tube, so that they hold the tube protector in place. Run a piece of tape around the tube protector to keep the 8 strip ends in place. Place the 2 "O" rings on the tube by rolling them over the pins and base of the PM tube. Now just below the tube protector base run tape around and build up a shoulder so that you can roll one of the "O" rings onto the shoulder and gradually make a very slightly snug fit "test fit" into the chamber. (Using this method you are gradually adjusting the diameter of the "O" rings). Now with the upper "O" ring fit adjusted and in place, go to the base end of the PM tube and do the same thing. Test the fit into the chamber, it should be just slightly snug, and so that the "O" rings do not roll off the tape. The "O" rings should be trapped between and next to the tube base and the tube protector base. Take a measurement between the 2 "O" rings and cut a piece of corrugated cardboard to fit between them and long enough to go around the tube. You want about an eighth of an inch space between the ends of the cardboard. Crinkle the corrugations so that it fits smoothly around the tube. Take a roll of black tape and start from one end of the cardboard and go around the middle, another turn and move to the upper end and so on for 3 turns. The last 6" of tape should not be stretched, just laid down to finish the wrap on the cardboard. Now coat the "O" rings with a light coating of silicone grease or release agent so that they will slide into the chamber easily. Do not use automotive grease, because it will deteriorate the "O" rings. Push the tube into the cleaned up chamber until 3/16" to 1/4" of the base is visible. Take a tube of black silicone sealant that you can get in any auto parts or hardware store, and seal the end of the chamber/base joint. After I finish running a bead around the joint I usually smooth out the silicone with "saliva" on my finger. Keep it wet otherwise you will make a mess. Water does not work as well. Let dry overnight.
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