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Tube hiss - any idea what's causing it?

I own an Eastern Electric M520 integrated amp that I am very fond of. However, recently I have noticed that there is a great deal of rather disturbing hiss eminating from my Omega XRS speakers once I power the unit up. The hiss does not increase when the volume is turned up. It's always there and very noticable during quiet passages. It's definitely a hiss and not a hum.

I checked the tubes and noticed that when I touch or slightly jiggle the front EF86 tubes, the hiss gets louder/softer when they are moved. Could it be that these tubes are going already? I do not have many hours on them. Maybe 100 at best. Should I consider replacing them or perhaps checking the other tubes too - perhaps the 5 AR4 rectifier tubes? I doubt it's the power tubes.

Do you have any thoughts/recommendations for me at this point. I am not sure how to proceed. As always, thanks for your time.
jpstereo

Showing 2 responses by herman

herman
2,215 posts
 
Well that is something that I overlooked. A solid state component common to both channels could cause the hiss. A rectifier or regulator perhaps.
herman
2,215 posts
 
The hiss is 99% for sure coming from the tubes. It is very unusual to get the results that Mr. Ghost did and have it go away. That is unless what he describes as hiss is actually something else. Corroded pins usually make more of an intermittent crackling sound than a steady hissing sound.

BTW hiss and microphonic are 2 different things. Hiss is just what it sounds like, a hissing sound that is steady. Microphonic means that external vibrations are picked up by the tube and you hear it through the speaker. If you yell at the tube and you hear your voice from the speaker then it is microphonic; meaning it acts like a microphone. You can also tap on the tube with something like the eraser end of a pencil and if you hear a ringing sound it is to some degree microphonic, but all tubes are if you tap them hard enough and tapping on hot tubes can damage them or cause them too fail so I don't recommend that.
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