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5 MA/DIV
1
VOL TS/D1V Ep
Control Settings for a 6 ALS Diode
PEAK VOLTS
SERIES LOAD
PLATE -GRID
PLATE -SCREEN-GRID
MA/D1V
VOLTS/D1V
100
51.:
PLATE
PLATE
5
1
Fig. 2-3.
Plate
Current
vs.
Plate Voltage
curve
for a 6AL5 diode.
Connect a
200
ohm, 2 watt resistor from the
c athode to ground to keep the power supply in
regulation. The curve can now be plotted in the
normal manner. The zero voltage point can be
determined by momentarily connecting the plate
to the cathode. Be sure the SERIES LOAD
s witch has put sufficient series resistance in
the circuit to limit the current to a safe value
when you do this. Position the line which you
obtain behind a graticule line. This line will
then be the vertical axis.
TRIODE C U RVES
By setting the PLATE-SCREEN-G RID and
PLA TE-GRID Controls to the proper positions
the following curves can be plotted:
plate
current versus plate voltage , grid current
versus plate voltage , plate current versus
grid voltage, and grid current versus grid
voltage.
Grid-Step Waveform
Triode curves involve the use of the grid
step generator in addition to the circuits used
in plotting diode curves. The grid-step wave
form is a stair-step waveform starting at
zero or some positive voltage.
It can be
s et to have from four to twelve steps going
n egative from ground or it may have as many
as eight positive steps above ground. In the
latter case the start of the stair-step wave
form is above ground.
The position of the
zero-bias curve can be determined by pushing
the Z E RO BIAS button.
The STEPS/SEC control provides a means
of selecting the stepping point of the step
generator. In the right hand pOSition, labeled
1 20,
the generator steps while the plate volt
age is at maximum and in the left hand position
the generator steps when the plate voltage
is at a minimum. In the
240
pOsition, stepping
occurs at both maximum and minimum voltage
points , and the faster switching rate reduces
flicker.
If
either end of the plate sweep is part
i cularly important, it is usually better to
s et the step generator to switch at the opposite
end. However, in some cases where no error
is introduced, the switching lines help to plot
a continuous curve between steps.
Plate Curren t vs. Plate Voltage
To display plate current versus plate voltage
cu rves the tube to be tested is connected in
the normal manner with the cathode to groun d ,
K , t h e grid to GRID A , or B connectors and
t h e plate to P.
Turn the PLATE-SCREEN
G RID and PLATE-GRID Controls to PLATE.
The following control s ettings should be
checked when a particular tube type is being
tested the first time:
1.
Set the HEATER Control to the correct
voltage.
2. Set the START ADJUST Control nearly
counterclockwise to avoid a positive grid
Voltage.
3. Set the PEAK VOLTS Control for a s afe
voltage.
4.
If high plate current is expected, set the
V E RTICAL MA/DIV Control nearly count
erclockwise to protect the small, low
current measuring resistors .
The other controls can be set after the
P O W E R - TEST switch is turned on and the
tube cathode has come up to operating temp
erature. Once the desired settings have been
obtained for a given tube type, other tubes
of the same type can be ins erted without
r e s etting the controls .
AA
O perating Instructions - Type 570
2 - 5
Summary of Contents for 570
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