The Avo Transistor and Diode Tester provides, in one
instrument, facilities for both transistor and diode
testing. The tester is a compact, simple to operate, direct
reading instrument, providing an accurate and convenient
method for the measurement of transistor and diode
Provision is made for the rapid and accurate measurement of
transistor hfe up to 1500 at a frequency of approximately
lkc/s and the measurement of leakage current between 1/xA
and 400mA for both p.n.p. and n.p.n. low and medium power
germanium or silicon transistors.
Both the forward and reverse characteristics of diodes can
be measured, the reverse characteristics at voltages up to
1000V under current limiting conditions.
0 to 12V stabilised and continuously variable. (Monitored by
0 to 1A max. Monitored by CURRENT meter, in 10 ranges from
50/u.A to 1.5A f.s.d. (first indication lju,A).
Less than 0.1/i.A min., approx. 50mA max.
0 to 1500 in 4 ranges. Accuracy ± 1.5% of reading, zfc 1.5%
of f.s.d. Measurement of hfe at collector currents lower
than about 250/a A will introduce progressively increasing
errors into the result.
Leakage Current: (IcEo)
0 to 400mA max. Supply current limited to approximately
400mA with SET VCe control fully clockwise. Monitored by
CURRENT meter on 10 ranges from 50juA to 1.5A f.s.d. (first
The collector power supply is protected against damage by
being current limited to approximately 4A on short circuit.
A 1A fuse in the collector power supply protects the lower
value meter shunts against overheating under heavy overload
A mains fuse protects against direct breakdown in the mains
The meter movement is protected by a heavy duty silicon
rectifier in shunt with the meter.
Forward Volt Drop: 5V and 1.5V f.s.d. measured across diodes
with a forward diode current of 0 to 5()()mA.
Breakdown Voltage: 0 to 100V at 3mA. Current limited on
short circuit to approximately 13mA.
0 to 1000 Volts at 200/xA. Current limited on short circuit
to approximately 1.3mA.
NOTE IMPORTANT. When the ‘SET V™' control is turned fully
clockwise and negligible current is being drawn it is
possible for approximately 140V to appear at the 100V
terminals on the 0 to 100 range and approximately 1200V at
the 1000V terminals on the 0 to 1000 range. Since the meter
full scale deflection is 100V or 1000V respectively, the
meter full scale deflection will be exceeded.
The instrument is housed in a strong metal case designed in
suitcase form for portability and ease of storage. The
mechanical structure is such as to provide inherent rigidity
of the assembly. The case contains the panel which carries
all the controls and within the lid space is provided for
housing the mains lead, a flying lead adaptor and a plug-in
adaptor for use with short-lead transistors, supplied as an
optional extra. When the lid is closed the case is
showerproof and the panel is completely protected against
Precautions have been taken to ensure that any loose
fragments of dust or metal inside the case do not interfere
with the operation of the instrument.
Using a length of transfer tape a thin film of adhesive is
deposited inside the case, in such a position, that any
loose fragments of dust or metal will be attracted to the
adhesive which will retain them indefinitely. .
All components likely to require replacement or adjustment
in service are conveniently located thus ensuring a maximum
of accessibility. The majority of components are located on
a hinged printed circuit board, this can be raised to permit
access to panel mounted components. The bolts securing the
printed circuit board form feet which protect the board from
damage if the panel is removed from the case. If the panel
is placed on a bench with the controls facing upward the
bolts prevent the printed circuit board from actually
touching the bench.
Dimensions: 15 in. x 9.5 in. x 5 in. (38 x 24 x 13 cm. approx.)
Weight: 21 lb. (9.5 kg.) approx.
Voltage: 110, 120. 200, 220 and 240 ±: 6%. The voltage is
set by selecting the appropriate transformer tapping.
Power: Approximately 50W.
The instrument is designed to operate in ambient
temperatures between 0°C and + 55'C.
The design of the instrument enables accurate measurements
to be made with the minimum of adjustments and setting-up.
The layout of the panel controls is such that operation of
the instrument, which centres around a FUNCTION switch and a
TRANSISTOR/DIODE SELECTOR switch, is largely
self-explanatory. These features together with the
protective devices incorporated in the instrument provide an
ideal tester for use not only by engineers and technicians
but also by unskilled personnel.
The instrument itself is protected against inadvertent
misuse and whilst testing faulty transistors and diodes a 1A
fuse in the collector supply protects the instrument from
damage if currents greater than 1A should be drawn. When
testing diodes in the reverse direction the short circuit
current is limited to approximately 13mA on the 100V test
and 1.3mA on the 1000V test. The controls are arranged to
give the highest possible degree of additional protection
during these diode reverse voltage tests. With the FUNCTION
switch set at VDR (the position for setting the diode
reverse voltage) it is also necessary for the TRANSISTOR./
DIODE SELECTOR switch to be in the DIODE position and
finally for the push button PRESS VDr to be depressed before
the 100V or 1000V can be obtained at the output terminals.
Transistors too, are protected to some degree by the setting
of the TRANSISTOR/DIODE SELECTOR switch. No meter reading is
obtained on the SET Vce position of the FUNCTION switch (the
position at which the transistor collector voltage can be
set) unless the TRANSISTOR/DIODE SELECTOR switch is set to
p.n.p. or n.p.n.
When testing transistors the nominal collector voltage may
be set down to zero. It should be noted, however, that the
measuring facilities in the collector circuit will introduce
a voltage drop. This could be as high as 300mV and will
result in the actual collector voltage being lower than that
indicated by the meter, by this amount. Due allowance should
be made for this when making measurements at low collector
The indicating meter has a 50¡xA movement and a scale length
of approximately 3.5 inches. Three simple scales calibrated
0 to 15, 0 to 50 and 0 to 100 are provided for all
measurements and a CAL mark for use during hfe measurements
is also indicated. This calibration mark enables the
measuring system to be accurately set up and ensures that
any slight variation in amplifier gain or oscillator output
level is adequately compensated for. All measurements are
indicated directly on the panel meter and full monitoring
facilities are provided. The meter is protected against
overload by a shunt silicon diode.
The panel markings are colour-coded, and basically all
markings around controls relating to transistor testing are
black and all those used during diode testing áre green.
Controls common to both measurements are coded in black.