Your new speakers are significantly more sensitive than your old speakers, so you're going to hear more system noise as a result.
The first step is to systematically replace the tubes in the Rogue with new tubes tested for low noise. I suggest Vintage Tube Services or Upscale Audio as sources for tubes tested for low noise.
Start with the small signal tubes. The EH and Sovtek tubes can be improved upon, and you likely will hear the results without any effort.
The horns that Klipsch used are brutally efficient/bright, and any noise upstream(like the preamp section of the integrated) will be brought out without mercy. Replace the small signal tubes with "Platinum Graded" ones from Upscale Audio, ie: the choices here- (http://www.upscaleaudio.com/12AU7ECC82_c_44.html) and (http://www.upscaleaudio.com/b12AX7ECC835751b_c_40.html) If you click on the tubes, you will be presented with the various grades available. While you're at it; upgrade to some quality NOS tubes and you'll be rewarded with a much improved presentation.
The sensitivity of the Klipsch is going to drive you crazy with tubes. There will always be noise, how much will depend on the tubes. You may be in for a lot of 'tube rolling' before you are satisfied. Your search for a quiet amp may be endless.
Well don't get discouraged. The others are right but you can have tube amps with your Klipsch and still have a decent noise floor without too much difficulty. My neighbor has LaScalas that are even more sensitive than your Cornwalls and we haven't had that many problems finding tube amps (and tubes) that are quiet enough.
Keep in mind though that some amps just inherently have a high noise floor, so you may not be able to save all of them with quiet tubes. I had a Rogue Magnum 99 for a while and it was pretty noisy, even with my 91dB sensitive speakers....
You made a great choice of speakers though! You have the potential of higher resolution than the majority of other stereo systems with those Cornwalls. Get them right and they'll knock your socks off.
Not an enlightened suggestion on my part but it might be worthwhile to call Mark at Rogue and see if he has speciifc NOS tube suggestions, or other ideas.
Prefacing this that I have a Cronus Magnum but it is driving 89db Tylers - Rogue had installed NOS Sylvania 12ax7 and au7s when they sent me the amp; and I currently have Siemens and Tungsols via Upscale in it now - like it with either "version"
As previous posters mentioned, your vintage Klipsch will pick up virtually any minor oscillations of the amp.
Technically I would experiment with adjusting feedback (obviously lowering the gain factor which may significantly help avoiding noise) along with adjusting bias current to the specified level of the THD which is more like re-tuning the amplifier.
Some suggestions. I use a pair of Klipsch Fortes, which are a bit less sensitive with your Cornwalls, with tubes and have no noise issues at all. But, I have a few suggestions for you. First is to really establish that it is the amp that is causing the trouble. Short one set of inputs and turn the selector switch to those inputs. If the noise is still evident your issue is the amp. If it is not, then the issue is your source. Buying quieter tubes is certainly an option, but an alternative is to call Rogue and find out if they can diminish the gain in the amp. You may find that this really knocks the hiss down, and it may also help you to advance the volume knob into the linear part of it's range, as now you are probably using it at the very beginning of it's travel, which sounds the worst and usually has the worst channel matching as well.
I am totally not up-to-date on tube equipment. Are test points and adjustment pots easily accessible??
I like the 'tune up' idea before any tube changes.
Lowering the gain of the amp sounds too much like a re-design?
I know this is a BAD thing to say, but SS?
Adjusting a gain very often is a feature of amplifier without any kind of re-dedign. It's rather 'adding' to an existing functionality and making the unit less-depended on tube quality. Most-likely, if higher quality tubes are purchased at the more than half-price the amp worth, the noise may still be an issue.
Tube amps are flexible in general in terms of adjusting a gain and/or lowering input sensitivity. The pot you need to install instead of feedback resistor to figure out the value at which the noise dissapears. Adjusting bias may or maynot be necessary neither on small signal or power tubes.
Congrats on your new speakers...I used to own Chorus in the late 80's. Klipsch'r really great w/the right tube amp. The Rogue is decent & very ballsy but noisy & somewhat unrefined & not quite 20/20 vision if you know what I mean. I was once the proud owner of a new Cronus hot-rodded to the max by Rogue w/their choice NOS tubes & it was somewhat noisy even w/my 92dB speakers & the bleed thru on the speakers while using the headphone section drove my better half crazy late at nite. I think if you find something more refined & perhaps triode driven you'll be in heaven. I'd love to try something like an Almarro 318B w/Corns....good luck.
Just get some small signal tubes that are graded low noise(even if they are cheap ones), and see if that doesn't ameliorate the problem. If your sources are not tubed, chances are they are not generating any hiss.
Many thanks for all your suggestions - I am going to explore them over the next few days. Mark O'Brian has always been super friendly and helpful - but I was really interested in what my Audiogon community had to say about the amp/speaker combo. I am going to try some new tubes first. And recheck all connections. The Cronus is my first tube amp and I love it - though part of the fun of this hobby s exploring new frontiers of sound - which I am getting in spades from these Klipsch Cornwalls - the sonic leap forward is huge.
Get the Quicksilver Horn Mono amps. No noise, no fuss and they sound great on high efficiency speakers.
Hi, I also own the Cornwall II's, and can definitely state that they are not the problem. Tube amps work wonderfully with them, even the flea-wattage ones. I would suggest that the brightness you don't like is probably coming from the Rogue amp - the Rogue amps are perhaps the brightest tube amps I have ever heard. This is partly because they are relatively high in wattage. I use a PrimaLuna amp, which is about half the wattage of alot of the Rogue stuff, and it has a much warmer sound. I would suggest that you try a lower-wattage amp than the Rogue, and you will probably find the sound you are looking for.
Call Rogue and find out which small tubes are in the gain stage, this would affect the hiss in the speakers the most. Then do as TVAD & Rodman99999 suggested and call either upscale audio, Brent Jesse, Jim McShane or Vintage tube services and get Phono grade tubes. Any brand of tube will lower your hiss in your speakers as long as they are low noise phono grade.