INTRODUCTION 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 characteristics. 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. SPECIFICATION Transistors: Collector Voltage: 0 to 12V stabilised and continuously variable. (Monitored by panel meter.) Collector current: 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). Base Current: Less than 0.1/i.A min., approx. 50mA max. hfe: 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 indication IfxA). Overload Protection: 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 conditions. A mains fuse protects against direct breakdown in the mains circuit. The meter movement is protected by a heavy duty silicon rectifier in shunt with the meter. Diodes: 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. CONSTRUCTION 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 accidental damage. 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. MAINS SUPPLY Voltage: 110, 120. 200, 220 and 240 ±: 6%. The voltage is set by selecting the appropriate transformer tapping. Frequency: 50—50()c/s. Power: Approximately 50W. WORKING TEMPERATURE The instrument is designed to operate in ambient temperatures between 0°C and + 55'C. TECHNICAL INFORMATION 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 voltage. 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.