Grid1 leakage can cause the tubes to change the bias, causing damage of tube or amplifier. Even so, gassy tubes can spark violently and unexpected, which may damage the amplifier or loudspeaker tweeters. Causes for Grid 1 leakage can be: Grid Emission, tube socket dirt (like fungus at the inside), leaky mica inside the tube, and bad vacuum (Gas). It is very hard to differentiate between various causes of leakage, and such a tube needs to be replaced, even if it seems to work at the moment. Socket leakage after long storage often improves after burn in, but it may come back later. Leakage must be tested under full dissipation, also the socket must be heated up fully. In this condition the tube should not fail the test. Specially grid emission appears only at full power, and will recude to acceptable level below appr 70% of maximum power. Yet such a tube is alway a reject, even when you do not use it at full power. Grid leakage will slowly increase over time, and when it becomes critical, suddenly the tube will overheat and damage.

Grid 1 Leakage can simply be done, by setting the parameter test know to Ic1 (some testers call it Ig1): So this is the next position after "S" (for transconductance). However, before you do, the internal nano ampere meter must be calibrated, and this is not eplained easisly in the Russian manual. This card shows it in an easy to understand way, with pictures. Size is the same as all other cards.