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
jea48
4,494 posts
 
>>"Jea48: You wrote: "If you put back in the three tubes you had pulled before the hiss, and you still have it, then I think that eliminates the tubes from the equations." I'm not following you. If I put the same tubes back in and the hiss is still there I don't see how I ruled out the tubes. If it is a bad tube, then wouldn't putting it back in cause the hiss to continue?"<<
[Snipes]
>>>>>>>>>>>>
I misunderstood the start of your thread. I thought you had reinstalled the original tubes, the tubes that were in the Line One before the hiss problem.

If the preamp did not hiss before you pulled the original tubes, but did after installing the NOS tubes, then I suggest you start from ground zero. Pull all of the 6 nos tubes and reinstall the original 6 tubes. Make sure you keep the right channel tubes separated from the left channel tubes when you pull them. If the hiss is not there, then that's great news.... That means that one, or more, of the nos tubes you pulled from the right channel is either shorted or has excessive grid emissions.

Post back after you install the original tubes.......good luck.
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Phd, the Sonic Frontiers Line one, two , and three, are not hybrids as far as I know. The SFL-1 is a hybrid.
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Jim

jea48
4,494 posts
 
Snipes, curiosity killed the cat!!
How about an update.....
Jim
phd
1,324 posts
 
Snipes, I agree with Jea48, let us know!
snipes OP
119 posts
 
I've been tied up this week. Plan to swap out all the tubes in the next day or two. I'll update the thread with my findings.
snipes OP
119 posts
 
No update yet. Hope to get to it this week.
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