Related Manuals for AVO 160A
Summary of Contents for AVO 160A
- Page 2 D5, R42 & R38: Anode voltage rectification added, components used D5 = D1, R42 = R38 = 100 kΩ ± 10% 1 W – this modification has been tested and proved to work in an original AVO CT160 and is also used by AVO in the AVO Mk IV.
- Page 3 Part 1: Modifications done by AVO AVO have updated the AVO CT160A to work more like the later AVO Mk IV in many areas, but not all. Apart from the looks on the front panels and the extra valve holder panel connected via the new contact on the original valve holder panel most modifications are easy to describe and understand if you understand how the original AVO CT160 works.
- Page 4 To measure rectifier valves on the 180mA range AVO have modified the CT160A in the same way that the AVO Mk IV is designed, with one extra resistor on the SET Ia & DR switch for the measuring range and also a resistor, R37, which is connected in parallell with the over current relay coil RL3.
- Page 5 Maybe this is a trade-off for some reason, maybe it was more expensive to have it there and have it changed in step with the grid volts switch, or maybe AVO found that it was not necessary to have that voltage there.
- Page 6 Diode and Rectifier testing on the ranges 60mA, 120mA and 180mA. Here AVO used two 3.9 Ω resistors in parallel with the relay coil RL3, which has a resistance close to 1.5 Ω in an AVO Mk IV, this will also mean a 57% decrease in current sensitivity.
- Page 7 AVO CT160A here in this circuit! Is this just a coincidence or something that AVO planned? My guess is that it is planned but the resistance for the resistors and RL3 will of course vary between each tester, but in the AVO CT160A service manual AVO says that these resistors will be "selected", which probably means that they are selected to work in...
- Page 8 It is quite long, but I really hope that you find it worthwhile to read through to the end! There is more to come in the future with a look at the Dutch Military special edition of the AVO CT160 named AVO CT160A.
- Page 9 400V tap on the HT transformer. AVO marked the taps on their HT transformer with the ‘mean voltage’, so it is labelled as ‘H400’...
- Page 10 For the anode current control measurements to be accurate, you must ensure that the remainder of the components in the AVO CT160 are within tolerance, and also that the tester is calibrated; however for the anode current controls in themselves to be accurate, you must ensure that a voltage of 1V Mean DC is developed across each of the 80Ω...
- Page 11 Part 3: Calibration resistors: To make sure that it is possible to calibrate the CT160 (and this also applies to the AVO Mk III and Mk IV) you will need to ensure that all the components are within the tolerance levels that AVO specified; not only the calibration resistors, but it is obviously worthless to have the correct value for the calibration resistors, if the rest of the tester is not within tolerance (especially the meter, anode current controls and 200Ω...
- Page 12 Page 11 of 17 In the AVO CT160, and also the Mk III and Mk IV, the same current is supposed to flow through the meter at the centre of the SET ~ calibration region on the meter scale. The centre of this area is usually marked by a red line, which is aligned with the 90mA line, or 90% of FSD.
- Page 13 CT160’s 66V rms circuit too; as it would then give you the same means of adjustment that is available in the AVO Mk III and Mk IV (the Mk III is more or less the same tester as the CT160, apart from some minor differences in both electrical and mechanical design).
- Page 14 However, I have been given such a schematic of an AVO Mk III, which I will come back to in the future, after I have checked it thoroughly.
- Page 15 When you are going to make the measurements on the AVO CT160 meter, I recommend that you use a small 1.2V NiMH battery, a few 1% resistors and three potentiometers (preferably 10 turn models for easier adjustment), one switch, plus a DMM (or an AVO 8) and some cables with crocodile clips for a quick hook-up of all components to check the meter movement.
- Page 16 Part 5: Meter protection: Since the circuit of the AVO CT160 is more or less the same as the AVO Mk III and not very different from the later AVO Mk IV, it is possible to protect the meter by the same means used in these other AVO testers.
- Page 17 There is some information on the Internet which says that there are two types of meters in the AVO Valve Testers, one at 30µA FSD and one at 33µA and with different internal resistance than the stated 3,250Ω.
- Page 18 NOTE: Never ever adjust the resistors inside the AVO Valve tester around the metering circuit if you are not absolutely sure of what you are doing! Changing one value will almost always affect all other values for all other ranges.
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