[Amps] AL-1200 Problem

[Donald Knight]

Hello Guys,
I was loading my AL-1200 up on 10 meters last night and all at once it made a strange noise and the grid current meter went to 0. The amp was still making full power out even after this happened. I've checked the zener diodes and they are good. Also checked the grid resistors on the meter board and they also check good. What I'm seeing now when I turn on the amp is it's pulling idle plate current and the grid meter pins negative just sitting there turned on and not even keyed up. It shows the correct 40ma in the cw position and 150ma in the ssb position but the amp is not even keyed up! Could someone please tell me what this might be and where to start checking for the problem? I did pull the tube out and turn the amp on and everything shows normal on the meters,correct high voltage and no plate current. Grid meter stays on 0.

                                                                                Thanks,Don Knight
                                                                                            n4dek