VCM 163 Valve Characteristic Meter Equipment

The AVO VCM 163 is one of the few tube testers (British: valve tester) being able to measure tube electrode currents, e. g. plate and screen current (fig. 1, left-hand meter movement) as well as mutual conductance (fig. 1, right-hand meter movement) simultaneously. The VCM 163 is the latest and most elaborate tube tester ever built by AVO. All volt
VCM 163 Valve Characteristic Meter Equipment - schematic

ages applied to the electron tube under test are pure 50 Hz line frequency sine waves. The plate (British: anode) as well as the screen electrode via diodes D1 and D2 are supplied with sinusoidal positive half wave voltages (cf. fig. 2). AVO unusually terms rectifier diodes D1 and D2 suppressor` diodes probably due to the fact that they suppress the negative half wave. Via diode D4 an unsmoothed negative half wave (grid BIAS) is applied to the grid electrode in proper phase relationship, i. e. anti-phase, to the positive electrode voltages. This is quite a clever and economical principle because the power supply becomes extremely simple (among other things no filtering). In addition power requirement of the line transformer (C core type) is half compared to a DC supply. AVO engineers have evaluated and verified that if alternating electrode voltages are applied in their correct proportions an amplifying tube (by virtue of its property of self-rectification) produces DC plate and screen currents, which for all practical purposes, bear an almost constant relationship to those obtained from its DC static characteristics. In the VCM 163 the following relationship between AC supply and DC static characteristics is implemented: The left meter movement (cf. fig. 1) reads DC plate and screen current continuously. As a further consequence of the fictive static characteristic of the VCM 163 test conditions of a tube can be directly...

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