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Slight hum from SLI-80 power amp

I own an SLI-80 Amp for a little over a year.  My system has developed a very low, slight hum only on the right channel. One has to get right up to the speaker to hear this hum, but it is still a hum that should not be there.
Any ideas where I should start looking to eliminate this hum?  Thanks
richfrank
sfar's avatar
sfar
1,771 posts
 
The first test I would do is to one at a time swap the matching pairs of tubes left to right and see if that switch moves the hum.
jtcf's avatar
jtcf
1,620 posts
 
A loose or dirty cable connection could be the culprit also.If the tube swap gives no results try cleaning all of the connections.
richfrank's avatar
richfrank OP
34 posts
 
SFAR & JTCF: Received both of your suggestions and will follow your advise. Will report back later. Thanks.
richfrank's avatar
richfrank OP
34 posts
 
Swapped the tubes. The very slight hum stayed on the right channel.
I replaced the rectifier tubes with 5AR4's [had previously 5U4's] and readjusted the bias to 80 mA. No change. I did install in parallel a REL Acoustic sub-woofer system as per wiring instructions over ONE year ago with no problems. I wonder if there might be a grounding issue somewhere.  Very frustrating. I am totally baffled.
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