Jeff of Arabica
Seasoned Member
  

Name the greatest of all inventors... Accident.
Posts: 968
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Hi Mike, Having the same Ultra pre-amp, I do have a couple questions. When you say you swapped the input tubes around in different configurations and the problem returns, are you swapping them within the same channel (i.e., Fronts, Rears, or Center/Sub)? As you know, the Ultra is comprised of three discrete pre-amps so I'm just trying to get a better sense of how you are troubleshooting this with regards to isolating the bad tube(s). That being said, if you are placing the tubes in different channels, is the hum moving to the corresponding set of speakers relative to where that input tube is placed? Or, is the hum always coming from the same speakers, no matter where the tubes are being placed?
Another thing to note is the Fronts channel does go through the Mix channel tubes so be mindful as you move the input tubes around. Those two input tubes above the Mix knob (far right side) could create audible issues in your two front speakers. .
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