Bill (Grannyring), I'm doubtful that it's a ground loop issue given that exactly the same symptoms occur when nothing is connected to the amp's inputs as when a component is driving those inputs. But it can't hurt to try a cheater plug to defeat the AC safety ground, and see what happens.
On the other hand, though, it seems conceivable to me that these symptoms might result with some designs BECAUSE there is no safety ground, due to a wiring problem in the house (or in this case, the apartment building). And also if the zero ohm connection that should exist at the breaker panel between AC safety ground and AC neutral is a significantly higher impedance, due to corrosion, looseness, etc.
Therefore I second Seikosha's suggestion of trying the amp at a friend's house, if possible. Or at least checking the outlets with a multimeter or an outlet tester. Post back, Scott, if you'd like further details on how to do that.
I'm assuming, btw, that the outlets are 3-prong types. Let us know if that is not the case.
Finally, regarding what appears to be a suggestion above to try the amp with no speakers or headphones connected: As most are aware a tube amp having output transformers should not be operated without a load. Otherwise there is a risk of damage or degraded long-term reliability to the output transformers and/or the output tubes, as a result of "inductive kickback." Although it is unlikely (but not totally impossible) for that to be a problem if no signal is being put through the amp.
Best regards,
-- Al
On the other hand, though, it seems conceivable to me that these symptoms might result with some designs BECAUSE there is no safety ground, due to a wiring problem in the house (or in this case, the apartment building). And also if the zero ohm connection that should exist at the breaker panel between AC safety ground and AC neutral is a significantly higher impedance, due to corrosion, looseness, etc.
Therefore I second Seikosha's suggestion of trying the amp at a friend's house, if possible. Or at least checking the outlets with a multimeter or an outlet tester. Post back, Scott, if you'd like further details on how to do that.
I'm assuming, btw, that the outlets are 3-prong types. Let us know if that is not the case.
Finally, regarding what appears to be a suggestion above to try the amp with no speakers or headphones connected: As most are aware a tube amp having output transformers should not be operated without a load. Otherwise there is a risk of damage or degraded long-term reliability to the output transformers and/or the output tubes, as a result of "inductive kickback." Although it is unlikely (but not totally impossible) for that to be a problem if no signal is being put through the amp.
Best regards,
-- Al