■ FIGURE 7. Top
■ FIGURE 5. The drilled box.
that side is small. Meter
calibration might be a
factor, but for home use
the tolerances are
acceptable, and adapters like this really help.
■ FIGURE 6. Base with
banana jacks mounted.
like these to test
components as shown in
Figure 2. Measurements
can be made on resistors,
capacitors, diodes, and inductors if the meter has
■ FIGURE 4. LC130 in action.
A Simple Test Fixture
Test Fixture Examples
A test adapter for attachment to coaxial connectors
is shown in Figure 3. Adapters like this have an
advantage in that they eliminate the need for a lot of
lead length from the measurement. So more accurate
results can be obtained. Figure 4 shows this adapter in
action: A Tektronix LC130 capacitance meter is measuring
a small capacitor. The marked value on the capacitor is
82 pF; the meter is indicating about 84 pF. Although the
meter was zeroed before the measurement, the
difference in reading could be from the component
tolerance or the extra lead length of the capacitor. One
side of the capacitor is at ground, so the lead length on
■ FIGURE 8. Our tester wired.
Fixtures quickly allow comparison of two devices to
be constructed. Test adapters of this sort are often
provided by manufacturers for their test instruments.
Tektronix offered an adapter that would do this, but they
are difficult to find and usually expensive. You can build a
simple box with a switch and two connectors to serve this
function. The fixture presented here is intended to permit
attaching to a transistor/FET curve tracer.
A small plastic box is appropriate for this project. I
used a blue plastic box to match the side cover colors
used on older Tektronix instruments. Figure 5 shows the
plastic box prepared for receiving components to attach
to a curve tracer. Figures 6 and 7 show the components
attached. (If you are using old stock components, be sure
to clean the contacts before you try to solder to them.
This is the voice of experience talking.
In Figure 8, the wiring has been completed. Since the
emitters of the test devices are at ground, only
the emitters and collectors need to be switched
from one transistor to the other; a double pole
double throw (DPDT) switch is required to
accomplish this. The long lead lengths do not
seem to present a problem in displaying
parameter curves, because the curve tracer
generator runs at 120 Hz. The schematic is in
The sockets used to construct this device
were (new) old stock, and were built to provide
■ FIGURE 9. Schematic.
BILL OF MATERIALS
ITEM MFR PART DIST PART
Plastic Box Hammond 1591MBU MOUSER 546-1591MBU BLUE
Switch (DPDT) Mountain Switch MOUSER 1081MD1T2B3M1QEEVX
Test Clips Grayhill 02-0 ALLIED 9487397
w/Banana Jack 02-1 ALLIED 9481000
Banana Jack Emerson 1080753102 MOUSER 5301080753102.
Transistor Sockets www.mouser.com
If you acquire a curve tracer made by
almost any vendor and perform testing on
transistors, there will be the opportunity for
the equipment to generate dangerous
voltages. Since some curve tracers supply
currents into the ampere range, combined
with higher voltages, you must be careful
not to exceed your limits. Happy testing!