my first gen. Model T is making a horrible crackling sound. i thought it was a microphonic preamp tube. i did the tap test and the tube to the far left crackled when i tapped it, but it did this with 4 different preamp tubes, so a bad tube was ruled out. does this sound like a bad socket? I cleaned the tube pins and socket with contact cleaner and still no change. if so, what size are the preamp socket holes on the Model T chassis?
