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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
carrington
1 posts
 
Ok, let's back up here for a moment. The hiss stays the same regardless of where the volume control is set? This isn't unusual since most input tubes come after the volume control. But the hiss is in both chanels, not just in one? Could be that both input or driver tubes have gone noisy at the same time - unusual but not impossible. I would probably contact the manufacturer for some ideas. It could be something simple like the EF-86's or perhaps the 12AU7's but it seems a little weird that tubes on both sides went down simultaneously. If I were you I would probably find some junker tubes (one of each - some end of life tubes would probably be just the ticket) and try them out in the various positions. Could be that the amp is burning up tubes because of power supply issues...
dweller's avatar
dweller
3,781 posts
 
Purchased a BAT 300X-SE and out-of-the-box it was hissing like a can of spray paint.
This was a constant hiss (both channels) and not volume dependant.
I didn't pee myself or throw a hissy-fit toward the seller but instead agreed to ship the unit to BAT for repair.
In a week or so, BAT shipped a fully repaired 300X to me and I've lived happily-ever-after. The repair cost me nothing.
BAT said the problem was a "voltage regulator".
jpstereo OP
53 posts
 
I replaced the 12au7s and I still have hiss in both channels. The EF86s are coming next week. If that doesn't clear things up then it's back to the manufacturer for a check up. Perhaps it is the voltage regulator.

Many thanks to all for chiming in on this issue!
herman
2,253 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.
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