In my previous two posts about the 04-500 and 04-548 X-ray source I showed you all the steps necessary to completely disassemble and reassemble the source and also how to install the new style filaments.
This post will explain how to install the old style filaments in a 04-500 and 04-548 X-ray source. Refer to the disassembly and assembly videos for more information on a complete tear down of the source.
The new style filaments comprise a single assembly where the filament posts are brazed into a ceramic base. The old style filaments use a scheme where one end of a coupler connects to the filament wire via a special pointed set screw and slotted ceramic. (A metal tube holds the slotted ceramic in place.) The other end of the coupler connects to the filament post. The coupler needs to be tight and also positioned equidistantly between the molybdenum block and the copper cap. The coupler also needs to be fairly close to the base assembly, but not touching. If you are not careful, it is easy to crack the slotted ceramic that the coupler sits on.
With that background information in mind, let’s go through the steps in the procedure:
- Remove the cap from the X-ray source.
- Use a tweezers to hold the coupler in place and remove the upper set screws on both couplers (per filament) using an 048-4 spline driver, then remove the old filament. Note that sometimes you just need to replace a broken notched ceramic and the filament may be reusable (if it is not warped or open).
- Remove the lower slotted set screw (this is a special set screw with a point on the end of it). Use a tweezers to hold the coupler as you start to loosen the slotted set screw, then hold the set screw as you turn it CCW and remove it from the coupler.
- Carefully lift the coupler off of the slotted ceramic.
If the slotted ceramic is not cracked it can be reused. Sometimes the copper wire that is inside the ceramic is over-compressed from the pointed set screw. If this is the case, you need to either replace the wire or rotate the wire by 90 degrees so that the tip of the set screw can compress into a fresh section of the wire.
If the slotted ceramic is cracked it needs to be replaced. To replace the slotted ceramic, loosen the set screw in the base about ½ turn CCW, which will release the tension on the metal tube. The metal tube does two things – it protects the long filament ceramic and also provides a mechanism for securing the slotted ceramic. The metal tube has a slot in it that should be positioned perpendicularly to the set screw. When the set screw is tightened, it compresses the metal tube which keeps the slotted ceramic in place. There is a second long filament ceramic that is inside the tube that goes all the way to the filament connector at the other end of the source.
- To install a new notched ceramic, straighten the copper wire (it has been compressed by the pointed set screw) so that the new notched ceramic can slide over it. Slide the ceramic over the wire and position it so that the slot is about ¼” above the base and faces the set screw in the base. The end of the metal tube should be flush with the base – you may need to remove the flange opposite the filament wire feed-through in order to use a pair of needle nose pliers to push the tube up. The slots in the tube need to be perpendicular to the set screw.
- Slide the coupler over the notched ceramic and check that the bottom set screw hole is lined up with the hole in the notched ceramic. Loosen the set screw and adjust the height of the coupler by pushing down on the notched ceramic until the bottom of the coupler is about .050″ (or just under 1/16″) from the base. Tighten the base set screw. The coupler should be facing roughly parallel with the moly block and be equidistant between the moly block and the inside of the cap. The inside of the cap lines up with the top of the copper tube. Adjust the height and angle of the notched ceramic as necessary.
- Check the height of the copper wire; it should be flush with the top of the notched ceramic. Trim if necessary.
- Install the slotted pointed set screw into the coupler. Once you get it started, hold the coupler in place with a tweezers so that the coupler is equidistant between the moly block and the top of the copper tube. You need to tighten the set screw until it is holding the coupler firmly in place, so by holding the coupler with a tweezers you can maintain the correct position and also prevent the slotted ceramic from breaking.
- Verify that the coupler is in the correct position and that it is solid.
- Repeat steps 6 through 9 for the other couplers.
Now you are ready to install the filaments.
- Carefully slide the filament posts into the couplers.
- One side at a time, install the upper set screw and hold the coupler with a tweezers as you tighten the filament. For now, tighten the filaments just a little bit as you may need to make some adjustments to the height.
- Repeat steps 1 and 2 for all of the filament posts.
- Set the height of the filaments. They should be .030″ below the moly shield. Adjust them as necessary to get the height correct. If they are too low you can raise the couplers if needed, but in general I have found that the couplers need to be pretty close to the base.
- Once all of the filament posts are at the correct height, hold the couplers with a tweezers and tighten the filaments firmly.
- If the filaments are not parallel to the moly block, hold the couplers with a tweezers and use a needle nose pliers to bend the top, flat part of the filament posts as needed so that the filaments are parallel to the moly block.
- When finished, the filaments will be at .030″ below the moly block and parallel to the moly block. The couplers will be firm and equidistant between the moly block and the copper cap.
The pictures below will help to clarify the steps provided in the above procedures. Once you have the filaments installed, the system should be baked out. The X-ray source then needs to go through the outgas procedure outlined in the PHI 32-095 manual. With these old style filaments, the more slowly you outgas them the less stress they will put on the couplers and the more reliable the source will be. If you outgas the filaments too quickly they can warp out of position and also stress the couplers, resulting in ghost peaks and possible shorting/arcing in the X-ray source.
RBD Instruments provides all of the rebuild parts for the 04-500 and 04-548 X-ray sources. You can find those parts on our website at this link: RBD Instruments X-ray source parts