Tech Note 1135 Detail

e/m Tube Troubleshooting

Affected Products:

SE-9638 e/m Apparatus

e/m tube troubleshooting

PASCO Solution:

e/m System Experiment Setup

  1. Operate in a dimly lit environment with a shroud over the apparatus.
  2. Fully seat the e/m tube into the socket of the coil base.
  3. Place the black cloak over the apparatus such that the cloak completely covers the rear and sides of the unit.
  4. Switch the toggle switch on the base to the e/m MEASURE position.
  5. Turn the current adjust knob for the Helmholtz coils to the OFF position.
  6. Connect your power supplies and meters to the front panel of the e/m apparatus, as shown below.

  7. Adjust the power supply voltages to the following levels:
    • Heater: 6.3 VAC
    • Accelerator Electrodes: 250 VDC (with the polarity as indicated on the base)
  8. Slowly turn up the current adjust knob until the Helmholtz coil current is 1.50 A (6-9 VDC). Power supply ripple should be less than 1%.
  9. Wait between at least 2 minutes or until the intensity of the electron beam stabilizes.
  10. Rotate the tube in the socket until the electron beam is in the same plane as the Helmholtz coils. (The beam should become circular.)
  11. Adjust the beam focus to obtain a beam of uniform width and maximal visibility.
  12. The visible linewidth of the reflection of the beam of emission should not be exceed 3.0 mm at the point on the scale either on the emission side or on the side furthest from the point of emission.

The beam is not visible or dim.

  1. If the e/m base was purchased before 03-01-2010, disconnect the power supplies, remove the cover from the bottom of the base, and check that the electrical connections match the schematic on page 5 of the manual. If not, please contact Teacher Support to return the base for modification.
  2. Check that your experimental setup is correct.
  3. If the beam remains dim, increase the heater voltage to 7 VAC for 7 minutes and return the voltage to 6 VAC. (Do not remain at 7 VAC for more than 10 minutes.)

The beam is visible, but helical.

  1. Rotate the glass tube and socket within the base to make sure that the beam is emerging along the plane of the coils. (When correctly oriented, the beam will be circular.)

If you continue to experience problems, the tube probably needs to be replaced. If the tube is covered by the 1-year warranty, please submit a photo of the beam with the serial number of the tube to Teacher Support.

Creation Date: 03/16/2011
Last Modified:
Mod Summary: