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.
Most likely the EF86's are microphonic, not necessarily dying. Its not unusual for tubes that sound OK at first get noisy shortly thereafter, depending on their initial qualities and how hard they are driven in the curcuit. You may need to focus on getting some 'low noise' tubes. Research the needs in your pre-amp for low noise tubes and if it has a reputation for needing low noise EF86's buy accordingly. I agree its not likely that the power tubes are going bad, and I doubt that its the rectifiers either.
I agree with Newbee's response - tubes can turn microphonic after they get some time on them - its not unusual for microphony to show up after a few weeks of initial use. Might be worthwhile to have a few extras on hand anyway, so getting some replacements to try will let you swap them around to locate which tube or tubes are the culprits.

Fwiw, tube dampers can ameliorate microphonics and give quieter output. Herbie's Audio Lab dampers are the best I've tried.


How do you like the Omegas. I am considering the XRS for a system up north in my cottage. I was thinking of driving them with a Cary CAD300SEI or SLI80.

Sounds like a bad tube to me I had one do a similar thing in a cj pre-amp replaced the tube and all was fine. I had a tube go microphonic in a different pre-amp which is characterized by you tapping on the or around the amp and the tapping eminates out your speakers.

The XRS are great and Louis is a wonderful person to deal with. My highest recommendation!
I just had a similar problem and it was not the power tubes, it was the driver tubes. It can't hurt to get a new rectifier tube(s) as you will probably need them one day anyway whether it is the problem or not. If the hiss is only coming from one channel, switch the tubes from the hissing channel one by one to the non hissing channel to find the culprit tube, process of elimination. Good Luck!

You know come to think of this , I have the same issue in my ARC ref 1, I just bought 4 matched sets of EH 6922 Gold pin, and it seems like one or more has gone microphonic, with my ear up close to the speaker you could hear a hiss and a bit of a hum, the hum being the lesser. Also it's seems less in the right channel than the left. I will be honest, I do not have any dampers on the tubes.
How can I rectify which tube(s) it the culprit? The tubes have less than 10 Hrs on them.

thanks in advance guys.
Check out the tube sockets ,sometimes they don't hold the tube pins tight. Erwin.
Try moving them around. I had some hissing and rotated all - Power and Pre-amp tubes, Left to Right. Checked bias and adjusted as needed. The hissing went away. Thought in my case it might have been an oxidized connection that changing out "fixed". In any case swapping all L to R seems to have fixed things - now for several months.
I switched all the driver tubes around L-R and I still have the hiss. Getting some new EF86s and we'll see what happens. Not sure what my options are if that doesn't work.
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.
Herman -
I definitely had "hiss"...constant very low level background noise in L channel as I recall. Could really only hear it when the volume was cranked all the way up with nothing playing. It was noticeable however as previously the JoLida had been dead silent. I think in my case, Bless (Erwin) above has hit on it...bad pin connection. Rotating and consequently re-seating all the tubes seems to have made a better connection and fixed things for me.

Jp - Hope you get to the bottom of it and it doesn't prove to be anything major. I'd also check all cables and interconnects. Funny how those things can manage to work loose...but you've probably already done this.
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...
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".
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!
Well that is something that I overlooked. A solid state component common to both channels could cause the hiss. A rectifier or regulator perhaps.