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Tube maintenance for Audio research sp-16 pre-amp

I have had occasional issues with background noise with the ARC sp-16.

A few months back, after bringing in the Bel Canto amps curently in my system, I noticed a faint but noticeable and irritating high frequency whine or tone when the system is on and no music playing. There is virtually no background noise otehrwise, so when this low level high pitch noise occurs, it is subtle but clearly noticeable. I re-arranged the 6 stock 12AX7 tubes that came with the unit and found that changing tubes around affected the noise. Eventually, I hit the right combo that eliminated the noise completely.

Yesterday, however I noticed the noise had come back. After checking all wires connections and such I then re-arranged the tubes again. The first try made it worse, then switching two of the tubes eliminated the problem again.

I am considering acquiring a set of 6 new tubes to see if that works to eliminate the problem again and then keep the old tubes as spares.

Questions:

1) I like the current sound and am not looking to change it much but am interested in advice regarding what tubes to use and where to get them.

2) Does this ring a bell with any tube gurus out there? has anybody had similar issues? Is this kind of noise as I describe it a common issue? Is it an indication of a bad or at least lesser performing tube or tubes in the bunch?

I'm also open to any advice regarding how to best handle tube noise issues when they occur moving forward. I tend to not like to have to fiddle around with this kind of thing, so any advice on how to best avoid this kind of issue down the road is appreciated.
128x128mapman
newbee
4,775 posts
 
Although you didn't make it clear I'm going to assume that the problem only arose in one channel (when it arose). If it occurred in both channels each time this solution wouldn't apply.

I think - you've got a bummer tube, or two. The switching around solved your problem because you positioned the bummer(s) in the least sensitive location. I have identical issues with my SP10. You can stop now and go back to listening to music, but do buy a spare pair anticipating they will fail before the others. Or you can put the new pair of tubes in the most sensitive slots and rotate the tubes after removing/replacing the tubes that buzzed (probably now in the least sensitive slots).

If you have had these tubes a long time just replace them with new tubes now and bear in mind that noisy ones can be rotated into the least sensitive slots and/or just replaced individually or pair at a time when the need arrises. Nothing wrong with keeping your present tubes for spares but weed out the buzzers. What ever makes you comfortable.

Re replacement tubes. It is best to get low noise tubes, that is tubes which have been actually tested for noise. This is not routine so you have to ask for it and you will be charged for it. That is one reason why ARC's tubes typically cost more. But I buy my tubes from other vendors because typically I don't care for the tone of the tubes ARC uses in their amps and pre-amps.

Oh, FWIW, tubes hiss and/or buzz to various levels of amplitude. This may only be a big deal if it bugs you. They may last just as long as a tube that is dead quiet. Tubes that crackle and pop get replaced once I'm certain that its not associated with problems arising from contacts in the sockets.

Hope that helps a bit.
thorman
1,262 posts
 
I guess my first answer would be to establish yourself with a good tube surplier..There are a handfull of good reliable sources that many of us use..These tube guys take a lot of time to pair and match tubes with double and triple testing..It may cost a couple bucks more but you can pretty much get the best quiet clean tubes around..

Names I might suggest to start with;
Jim Sautter ( audiogon member )
Andy ...(Vintage tube Services )
Jim McShane ( Jim McShane tubes )
This is at least a good starting point.Good Luck..
mapman's avatar
mapman OP
22,407 posts
 
NEwbee, yes, the noise was in one channel only.

More of a very high frequency whine, like a dentist drill, but very constant in tone, than a "buzz". Not very loud either, you have to mute and unmute the pre-amp to be sure it is there unless you listen right up in front of the tweeter.

Which are the least sensitive tube positions in the sp-16? There are 3 tubes in the pre-amp section and 3 in the phono section. The noise has been associated with any input hence I assume the pre-amp section, not the phono section.

I will likely lean towards Arc for the tubes unless someone can tell me something specific about other tubes that might offer improvement in some way without having major impact on the general sound.
rrog
1,958 posts
 
Mapman, That's exactly why you want to stay with ARC tubes, because you don't want to change the sound of a great sounding preamp.
thorman
1,262 posts
 
Just keep in mind Audio Research does not make tubes..They buy just like all of us..The just have them screened and re-lablelled for them..They can get a bad tube also..By buying yourself,you can get the same tube without the cost of the middle man ( Audio Research )..It requires more work on your part but,can be rewaring if you don't mind the extra work involved......
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