You should be able to do the grid leakage and shorts test on both plates of the tube--not sure what is causing the problem here--dirty switch--faulty wiring--bad solder joint? Dirty tube socket could also be an issue. Grid leakage test can be tricky, and sometimes requires a selected tube--according to the manual.<P>Same suspects for lower test on G2/P2/K2 setting. You'd have to know that a certain tube tested a certain way on a TT1A to eliminate the tester from the equation.<P>"Ping"--what does that mean?<P>------------------<BR>