First, be cautioned that voltages in the neighborhood of 10,000 V are present at the wires which lead from the power supply to the back of the tube cabinet. When the power is on, stay clear of these wires. The face of the tube and all metal cabinets are maintained at ground potential, so there is no danger at these points.
Before turning the power on, be sure that the ACCELERATING
VOLTAGE control and the INTENSITY control are turned fully
counterclockwise.
After turning the power on, wait about a minute for the
EDT filament to warm up. Then increase the ACCELERATING VOLTAGE
slowly to about 7-8 kV. Note: the ACCEL. VOLTAGE meter is a 0-100
microammeter in series with 100 megohms. Therefore, the meter reads
0-10 kV and the meter scale is easily converted from
to kV.
Then slowly increase the INTENSITY until a spot is seen on the EDT
screen. At this time note the target current.
It should be below 
(1/10) of full scale. Don't operate the tube at higher currents!
At higher accelerating voltages even smaller currents are required
for good results. Excessive current will not only burn up the
target, it will damage the phosphor screen. Adjust the focus knobs
(coarse and fine) to obtain the smallest, regularly shaped
spot possible. The best
focus control setting is affected by the accelerating
voltage so that some focus re-adjustment is necessary from time
to time.
Move the spot around with the position controls to obtain the diffraction pattern desired. The graphite is in the upper left quadrant of the target and aluminum is in the other three. Generally it is easy to find a place on the target where a good circular pattern for polycrystalline aluminum is obtained, while it requires a lot of hunting to find a place where a good hexagonal pattern from graphite is seen.