Funderberg gold sputter test:

See Figure 24. The powdery looking material on the paper is gold meltballs.

Use a high-pot tester to apply 2x the rated anode potential. The grid is at ground potential. If the positive leakage current is much higher than the negative leakage current, gold-spluttering is indicated. To reduce gold meltball leakage between the anode and the grid, hold the tube upright and strike the top of the plate cap vertically with the flat side of a 4oz ball peen hammer. Tapping will dislodge gold meltballs, which will then drop into the tube base. The leakage current should decrease. When measured leakage current stops decreasing, stop tapping. Do not invert tube or the process will have to be repeated.

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