Want more high frequency extension

Well, I guess I agree with Tvad, I would switch out the Bugle Boys first. It's cheap, and while they provide a smooth sound, they aren't very extended on either end of the spectrum.

However, I suspect you still may not be satisfied. Can you please let us know what speakers you are running?

Very pertinent points you raise, Eldartford.

While the Granite schematic is available to me, I have not asked for it, and do not have it. From their advertising, the amp is zero feedback, based on that setting. A switch controls whether the amp runs in triode or ultralinear (pentode), which I keep in triode with the KT88 tubes. And, while I have not measured the sound using feedback versus no feedback, it is instantly apparent there are dramatic differences between the two. Others who have come to listen cannot believe the degree. I could plot a response curve using a test CD, but in all honesty (and not to be a wiseacre), I always prefer listening to music as opposed to test tones.

I also concur that loss of HF hearing should not be used in any way, or at any time, as a barometer of one's ability to judge a system. Using a test tone (yes, I do use them at times), on my Fried speakers, I was able to hear the 16 kHz tone, but not the 20 kHz. I didn't much care, as I said, I prefer listening to music (which I probably the reason I didn't then go try the 20 kHz tone on my Coincidents), but the Frieds are only rated to 18 kHz, so I am now unsure if my inability to hear the 20 kHz tone was a reflection of the speakers or my own hearing. I do know most men cannot hear to 20 kHz.

Mattybumpkin, I gave the JJ E34L tubes a go last night. They were much less sparkly than the JJ KT88, so that should be a real consideration in your quest. Whereas the KT88 have a beautiful, sweet, extended signature, the E34L were much more flat in tone. It was akin to adding feedback, but not to the same degree in terms of magnitude. The KT88 were obviously much more powerful and extended at both ends of the spectrum.

I then leveled the playing field a bit by then running the E34L in ultralinear. While the sonic signatures of each tube remained, the power differences were more or less canceled. The E34L produced better bass than I expected, but the KT88 were still superior.

Based on what I heard last night, and what you are looking for, the KT88 are the more than obvious choice. Still, as you pointed out, you will have to wade into these waters VERY carefully, to avoid the issues others have faced in running this tube in the SixPacs. Due to the cost of the larger tube, it is not something to get into without being certain of the result.

Good luck!

Matty, the Green Mountain speakers are definitely NOT the problem. While I wouldn't call them bright, the word "engaging" comes to mind.

Also, zero feedback tube amp are more forward than those with feedback, in my experience. The differences are not even close. Right now, my current amps allow one to dial in increasing amounts of feedback, and adding feedback only serves to destroy the sound by taking away extension at both frequency ends and removing all of the music's excitement.

Tube amps with no feedback are also, in my experience, those most reflective of the sonic signatures of their tubes. By applying feedback, you get away from that. In your case, you can use it to your benefit.

Your preamp is known for being on the exciting side, so I would still first change out the Bugle Boys for something more extended. Try Siemens 6922, as they are on the opposite end of the spectrum from the Bugle Boys.

After that, I would roll the tubes in the SixPacs, beginning with the EL84, then moving to the output tubes. One thing I would worry about in going to tubes other than EL34 is the issue many have faced in doing the same thing with the Cary V12. Surprisingly, many here who have tried KT88 have noticed less excitement, jump, power, and bass when moving from the EL34. Despite their speaking to Cary regarding the bias settings, I am 100% sure that the bias settings for these larger tubes is set too low based on the sound.

One EL34 flavor which is more bright than you have now are the JJ E34L tubes. I have a quad of blue E34L coming today, so I maybe able to give you a report on how they compare to my JJ KT88.

But, and this requires a big leap of faith, and the ability to do it, the biggest improvement I have been able to wrest from my system this year was REMOVING THE PREAMP altogether! Running CD direct, straight into my tube power amps increased the jump factor more than I can ever convey. It is one of the biggest improvements I have EVER seen. I was running a Blue Circle BC3, and removing it ratcheted up the excitement, immediacy, slam, bass, power, everything. In later trying a Joule LA150, which was clearly superior to the Blue Circle, the sound was still no match whatsoever for having no preamp there.

The question is, can you do this? Do you spin vinyl? Do you run more than one source? Do you have a CD player with variable out? Are you willing to try one? What about using something like the EVS Ultimate Attenuators? While it is simple, it isn't for everyone...