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Ringing from the tweeter

Hello fellow Audiogoners,

The ringing began about a year ago or longer in the left tweeter. It sounded like tuning in to radio stations in the old days, which I attributed to my Rogue Audio 99 preamp's tubes going bad. At first it was intermittent, then more and more present. It was audible and annoying when changing sides or records, even with the volume all the way down, but not apparently audible with the music. I had a rare listening session when the ringing was not there, but once it began it was pretty much always there. Muting the preamp would get rid of the noise so I assumed the problem was the preamp tubes, not my M-180 tube monoblocks.

About a month ago, I installed new tubes in the preamp, four NOS hand-picked and thoroughly tested by Andy from the VTS. The tubes are dead quiet and sound terrific, but just a week or two after I put them in, the ringing from the right tweeter this time began again, first intermittent, now pretty much constant, just as before. Again, muting the preamp gets rid of it.

Andy told me that the 6SN7 tubes should last years so I'm quite upset the problem returned so fast. Any idea what may be causing the ringing other than the new tubes going bad so fast? Is the preamp somehow “overstressing” the tubes, for lack of a better word, and needs to be checked out? The tubes are the type that can handle higher voltage, btw. The only other source would be my solid state phono preamp or the cartridge, which I think is rather unlikely.

I’d appreciate your opinion or suggestions.
actusreus

Showing 2 responses by mulveling

mulveling's avatar
mulveling
2,134 posts
 

(aware this is a very old topic) The Rogue 99 is a VERY high gain tube preamp. Combining this with NOS 6SN7GT tubes is bad news. No matter how well screened and low-noise selected the tube guy says they are, older GT series 6SN7 are not usable in the 99’s right-side slots (as you face the 99’s front) without noise gremlins. You can maybe get away with them in the left-side slots, but they will also have less sonic impact in those slots. The right-side slots "see" the most downstream gain.

My recommendation is to stick with modern Russian low-noise selected Tung-Sol 6SN7GTB (e.g. Upscale Audio’s Platinum grade) and/or try the later GTA and GTB series Sylvania tubes (angled black plates), which have a design that lowers their microphony (I prefer the tall bottle variants). Some other brands of vintage GTB might be quiet too (Raytheon, RCA), but I haven’t personally tried them in this unit. I know the vintage Tung-Sol GTB are generally quiet, because they used the same Sylvania GTB plates. If you really want to avoid modern tubes, you can try NOS 6SN7GT in the left slots and vintage 6SN7GTB in the right slots.

Ringing or whistling sounds just go hand-in hand with those older GT tubes in high-gain slots, unfortunately. You might think you’ve found a magic "quiet" set, but more often than not it won’t last (as you’ve found). These 6SN7GT tubes have very large plates compared to 12A*7 series tubes, and those 80 year old micas aren’t holding things down firmly enough for the gain levels involved. I do love the older 6SN7GT in power amps, where they are far enough downstream to not surface their noise issues, but still have a big impact (positive) on sound.

mulveling's avatar
mulveling
2,134 posts
 

What’s a “high gain” slot in an all tube device? The tube supplies any gain, so gain cannot be greater than what the tube can provide.

It means you add up all the net gain you see downstream, starting from that slot (inclusive). Add in power amp, and account for speaker sensitivity. The 99’s tubes come after volume attenuation, so that doesn’t help. The right-hand slots in the 99 account for the 1st stage of amplification, so they are more sensitive to noisy tubes. The left-hand slots come after (mu-followers), so their noise issues don’t get subjected to the amplification of the 1st tubes. I have experience with this unit. It was not RFI / EMI, at least in my case, though it's quite possible that was OP's problem.

At 23dB, it is a high gain preamp. You add a high gain amp (which many of Rogue’s own amps are), add sensitive speakers (like my Tannoys), and you will have problems with old 6SN7GT’s in those slots, guaranteed. The 99 mostly shipped with cheap Chinese Shuguang 6SN7, which honestly I wouldn’t trust to be low noise either. New (screened) Tung-Sols or vintage GTB’s are the best bet.

I’ve said for a while Rogue needs another reference rig with high sensitivity speakers, so they can hear some of these things for themselves.

Yes, I agree in general most of the old "best sounding" 6SN7GT’s from the 1940s are not usable in line stage slots due to noise / microphony.

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