11-010 Electron Gun Control modification to reduce noise

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Due to aging components, many of the PHI 11-010 5kV electron gun controls have developed a slight noise problem in the emission chopper circuit on the 623 board that results in about 300 mV of 60 hz ripple on the emission voltage, which translates into noise in the electron beam and Auger data.

Since the chopper circuit is never used (it was designed as a way to get N/E data with a lock-in recorder), a very simple solution to the problem is to bypass the chopper circuit.


  1. Unplug the 11-010 AC power cord and remove the cover.
  2. Solder a jumper between Pins 17 and 18 on the 623 board as shown below.  The 623 board is located on the side of the 11-010, just above the filament supply board.

This modification will reduce the noise level from about 300 mV to 50 mv or less and results in noticeably cleaner Auger data.

Chopper board resistors
This jumper will bypass the Chopper board circuitry
Chopper board schematic
Jumper location on Chopper board

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