2. amps-preamps
  3. 1142033337

preamp tube hiss from my SF Line 1

I'm trying to diagnose a very audible hissing sound that recently showed up. The symptoms are, hissing sound coming from the right speaker. Its very noticable from my chair. It does not get louder as I turn up the volume. The sound is there regardless of which input I select. It does go away when I switch on the HT Passthrough. I thought I had a bad tube and have tried swapping out each of the three tubes ont the right channel and it makes no difference. All the tubes are NOS Amperex and I've been using them for a while now without any issue. This all started when I swapped out the bottom pair of tubes with some better ones that I had. All my tubes were recently tested so I know they still have plenty of life in them. Any ideas? I find it unlikely that I have multiple noisy tubes, but of course I could try putting the stock ones in all three right positions. Any insight would be appriciated.
snipes
gnobber
43 posts
 
I just experienced a static/hiss last night for the first time. Kind of like when a turntable reaches the end of a record. Not noticeable during music, but noticeable when I hit 'pause'. I swapped cables on the amps and source, and isolated it to one side of my preamp (BAT VK30, with 6 6H23 Russian Rocket logos, 2.5 years old). Later that evening, the noise mostly went away. So, I was wondering . . .

-should I isolate the one bad tube and replace it?
-or, should I replace a pair of tubes to keep the same age on them?
-just wait for the noise to come back?
-is this noise a warning that the tube will have a catastrophic failure in the near future?

thanks for your help and advice
snipes OP
119 posts
 
My problem turned out to be two seperate tubes were making noise. It took a while to troubleshoot, luckily I had a nice stash of extra tubes to mix and match while trying to isolate it. I'd just replace the problem tube unless they are inexpensive and you think they are getting up there in age.
gnobber
43 posts
 
Thanks for you reply, Snipes.

In my case the problem came on suddenly, so I would think it would be one tube vs. two. Do you think 2.5 years is 'getting up there in age?' I probably do 5 hrs per week, so maybe 700 hrs at this point?
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