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Tube preamp noise question

I have a question for experienced tube preamp users. I purchased my first tube component, a preamp, a few months ago and am having a noise issue. It uses 5881 and 6SN7 tubes for their respective functions. I have not yet contacted the manufacturer because I wanted to sort out the issue myself if possible. The noise I hear is somewhat like the crackle and pop of a scratched LP. Sometimes, it could also be described as like the “roar” of a natural/propane gas flame (e.g. Bunsen burner), and sometimes it sounds like “squeaking” of Styrofoam rubbing, etc. It comes and goes and does not seem to go away as the tubes warm up. At first it was only in my left channel so I swapped the tubes from L to R but the noise remained in the L channel. My thinking at that point was that it wasn’t tube related and must be something in the electronics of the pre. After a month or so, now the same of noise is appearing in the right channel as well. The noise is not subtle and can easily be heard while music or a movie is playing. It’s embarrassing when having friend over as well.

My question is what may be causing this? My speakers are sensitive (95 db/w) so not sure this could just be tube rush because of the volume and intermittent nature, but I'm not familiar with tubes enough to rule that out. Is it a case of noisy tubes that I can replace or should I be concerned about the innards of the component? I appreciate any insight and thoughts you may have.
gjames
musicslug
430 posts
 
welcome to tubes! the good news is that a lot of issues that will come up simply involve replacing tubes. you need to know which tubes do what (L or R, phono or line, etc. - do you have the user's manual?), then start using logical deduction to figure out where the problem tube is. e.g. is the noise on both channels? is it phono only or all inputs? having a spare set of pretty much any tubes you use is definitely worthwhile. not a bad idea to keep a log of what tubes you've changed out and when...

p.s.turn off the power when taking out tubes!
dfhaleycko
178 posts
 
Another possibility you might consider is dirty tube sockets, particularly on older tube gear. Parts Connexion offers slender nylon brushes that can be used to clean tube sockets. A fine brass brush can be used to clean tube pins as well. Sometimes crackling noises in tube gear are solely due to poor or erratic connections to the tubes.

HTH!
gjames OP
35 posts
 
Thanks everyone for the responses. It sounds like the consensus is that it is tube related. I'll report back with my results.
atmasphere's avatar
atmasphere
11,831 posts
 
Gjames, if the sound appears only in one channel, the first thing I would do would be to swap the interconnects from the preamp to amp, left for right *at the amp input only*.

See if the problem moves. If it does not--> amp
if it does --> preamp

The compalint sounds like a microphonic tube, and swapping it did nothing, but what if it was in the amp?
gjames OP
35 posts
 
As promised, I have an update to the original post. The problem was in the 6SN7 tubes. Thanks to McFarland who graciously supplied me with some spares that he had on hand, I replaced the stock tubes and voila, no more of the noise that was present before. Thanks to all who responded and pointed me in the right direction and most of all to Mcfarland for supplying the replacements. Now I'm off to find some good NOS 6SN7s to take up permanent residence.
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