Hi, I need help. Last August I purchased a new LP27a preamp (uses either 65 or 27 tubes, 6BX7, and 80 rectifier). I'm getting an increasingly annoying hum with this preamp. It sounds like a ground loop? I have swapped out the 80 tube several times and tried different 27 and 56 tubes to no avail. I tested the 6BX7 tube and it tests strong.
The hum will occur just turning on the preamp and connected to my amp with no inputs into the pre. I have several tube, solid state and hybrid amps, and they all hum.
Currently, I stopped using this preamp. Does anyone have any suggestions on how I can trouble shoot? Any suggestions as appreciated, thanks.
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