>I am working on my sons amp which blew up with a loud bang. What
>I have found so far is one tube with a grid to cathode short
>when filament voltage is applied.
** grid/cathode shorts are typically caused by cathode flaking. [
photos in Sept/Oct 1990 *QST* ] This can result from inadequate warm-up,
more than 350mA continuous cathode-current, or an intermittent parasitic
oscillation. I would test the tubes with a high-pot tester for the
presence of gas or evaporated gold. Leakage should be under 5uA @ 5kV
positive and negative on the anode with the grid grounded. More leakage
current with positive V on the anode means loose gold.
- R. L. Measures, a.k.a. Rich..., 805.386.3734,AG6K,