There are two issues being discussed in this thread: the original issue of a transformer hum and hum coming out of speakers. They are two separate issues. The transformer hum is mechanical, the speaker hum is electrical. Hum out of the speakers is caused by one or more ground loops in the system.
Mechanical hum is caused by other issues, typically: a DC offset in the AC line; electrical noise in the AC line; a poorly designed or implemented transformer; or an old transformer.
I have three essentially identical amps that are about 25 years old. The transformers in them did not hum, at least audibly, when they were new. Now I can hear them from across the room. Everything I read indicated that since the noise was constant and occurred with no fluorescent lights on and no motors running that it was caused by DC on the AC line. As it happens, I built these amps at a company I used to own. I consulted with my ex-partner, the design engineer and he said he doubted there was DC on the line and that the transformers, which are toroidal, were probably just old and the windings had loosened slightly. I decided to build a DC blocker anyway. It didn't help. I tried an isolation transformer. It didn't help. I then built a fixture to measure any DC offset on the line. What do you know, it was zero.
In the end, I moved the amps to the room behind the front listening room wall. All's quiet on the listening room front.
oldschool1 - I suspect the right transformer in your amp is humming louder because the bias on the right channel is slightly higher.
Mechanical hum is caused by other issues, typically: a DC offset in the AC line; electrical noise in the AC line; a poorly designed or implemented transformer; or an old transformer.
I have three essentially identical amps that are about 25 years old. The transformers in them did not hum, at least audibly, when they were new. Now I can hear them from across the room. Everything I read indicated that since the noise was constant and occurred with no fluorescent lights on and no motors running that it was caused by DC on the AC line. As it happens, I built these amps at a company I used to own. I consulted with my ex-partner, the design engineer and he said he doubted there was DC on the line and that the transformers, which are toroidal, were probably just old and the windings had loosened slightly. I decided to build a DC blocker anyway. It didn't help. I tried an isolation transformer. It didn't help. I then built a fixture to measure any DC offset on the line. What do you know, it was zero.
In the end, I moved the amps to the room behind the front listening room wall. All's quiet on the listening room front.
oldschool1 - I suspect the right transformer in your amp is humming louder because the bias on the right channel is slightly higher.