Tuesday's bench session gave me a clean 60Hz hum, then Thursday ruined it

I spent Tuesday wrestling a 5E3 build that had a nasty 60Hz hum no matter where I moved the heater wires. Moved them tight against the chassis, twisted them perfectly, and got it dead quiet for about an hour. Thursday morning I fired it up and the hum came right back, louder than before. Turns out my grounding star point at the input jacks worked loose after a week of vibration from my drill press sitting on the same bench. Has anyone else had a ground point that seemed solid but needed a locking washer or a second nut to stay put?

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sam5302mo ago

Man, did you try putting a little thread locker on that ground screw? I had the same thing happen on a Princeton build once, the star washer just wasn't cutting it. I ended up using a locking washer AND a dab of blue Loctite on the nut, then cranking it down with a real wrench instead of just finger tight. That thing has stayed put for two years now, even with my kid slamming doors in the same room. Also check if the solder joint on the lug itself is good, sometimes the wire breaks free inside the solder and only shows up after the board flexes a bit. A second nut as a jam nut works too, but I found the Loctite way less annoying to deal with if you ever need to swap parts out later.

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