15-255G Filament Change Procedure

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This post explains how to replace the C75-010 tungsten filament used in the Physical Electronics 15-255G double pass CMA.    Refer to the pictures below for more details.  RBD Instruments provides the C75-010 filaments as well as any other parts that you may need for your 15-255G analyzer.  We also offer a complete analyzer rebuild service that includes a new filament and electron multiplier.

15-255G Filament Change Procedure

 Use gloves, de-magnetize all tools and clean all tools with Isopropanol.  Set up a work area with UHV aluminum foil.  Or use regular aluminum foil and clean it with isopropanol.

Set analyzer on stand or use manuals and support analyzer on handles, facing up.

  1. Remove outer magnetic shield (3 screws)
  2. Remove inner magnetic shield (4 screws)
  3. Carefully remove conical ceramic cover.   Note that sometimes the conical ceramic will stick inside the cover. Be careful not to let it fall out if it does stick. If it falls out an breaks a replacement conical ceramic is expensive!
  4. Remove conical ceramic and carefully set it on the aluminum foil.
  5. Carefully lift inner cylinder up and off of the electron gun assembly. Note: If the inner cylinder does not move freely, use a heat gun to expand the inner cylinder so that it will slide off. Do not force it! Be careful not to damage the grids.
  6. Look at the electron gun detail to familiarize yourself with the electron gun assembly.
  7. Remove the deflection cover (3 small flat head screws)
  8. Remove the deflection support screws (4 flat head)
  9. Remove the deflection support post that is located between the two ceramic posts.
  10. Tilt the electron gun out and down so that you can access the bottom plate of the electron gun.
  11. Remove the three long screws that hold the electron gun assembly together.
  12. Remove the V1 emission screw
  13. Remove the 2 filament couplers from the filament posts. You will need a .048 4 spline wrench.
  14. Remove the 3 filament support ceramics.
  15. Remove the filament whenelt cap assembly. Note the orientation of the emission tab and filament posts as when you put the new filament in it will need to have the same orientation.
  16. Remove the 3 screws that hold the filament base on and remove the filament.
  17. Install the new filament in the same orientation as the old filament into the emission cap.
  18. Install the 3 screws and the filament base and tighten slightly.
  19. Position the filament so that it is centered in the hole and tighten the 3 screws. This is best done using a microscope. For best results the tip of the filament should be perfectly centered.
  20. Install the filament assembly on top of the 3 filament support ceramics and use the 3 long screws to hold the assembly together. The three long screws need to be tightened firmly so that they all have the same distance with respect to the base.
  21. Reconnect the V1 wire
  22. Reconnect the filament couplers.
  23. Install the deflection support post, screws and cover.
  24. Ohm out the connections to the filament and V1.
  25. Degauss the gun assembly.
  26. Install the inner cylinder over the electron gun assembly.  Line up the dead spots on the ceramic tubes.
  27. Reinstall the upper outer cylinder.
  28. Carefully install the conical ceramic. The resistor part should be 180 degrees out from the center flat ceramic. Ohm out OC (outer cylinder) to ground and make sure it has the correct resistance of 600 k ohms +/- 100 k ohms.
  29. Install the conical cover and tighten the screws firmly and evenly.
  30. Install the inner magnetic shield
  31. Degauss the analyzer.
  32. Install the outer magnetic shield.
  33. Degauss the analyzer. Installation complete.


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2 thoughts on “15-255G Filament Change Procedure

  1. Hi,
    Unfortunately, I broke the conical ceramic of the CMA. Can you please let me know about its price? The model is 10-155.
    Best regards,

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