The AVO Valvetester is a simple valve tester that works on the basis of steepness. The steepness (Trans Mutual Conductance) is often expressed in mA/V. The value of the steepness shows the extent to which the valve is still in order, and the wear and tear can therefore be measured. The tester itself consists of 2 separate panels. The settings are universal and in principle you can test any valve, including the newer types. For this, gradient feet were later released, as well as separate panels with other valve feet. First of all, the right filament tension must be chosen. The principle is according to the backing off principle, that first the mA/V controller is set to 100 mA/V. The Zero controller is located on the far right, and when the valve warms up, a measuring result takes place and after about 1 minute the zero controller must be set to 0 mA/V. After this, the mA/V can be set according to the AVO datasheet manual. If necessary, the Zero controller still needs to be set to 0 mA/V. After the valve is set according to the extensive AVO data manual, the valve can be tested.