Want more high frequency extension

I like my current set up, however, I find the high frequency extension to be lacking. Any thoughts on how I can achieve more extension? I was thinking one of two areas, preamp change or tube rolling in my amps.

I currently have an Audible Illusions L-1 with Bugle Boy 6922 tubes. I was thinking of maybe trying a passive pre like a Placette or trying a SS pre. thoughts?

Alternately, I was thinking of rolling out the stock tubes in the Six Pac's. Right now they are Rubey Tubes El34's for the output tubes, Electro Harmonix EL84EH for the current source, and Westinghouse 12BZ7 for the gain/phase inverter. The amps will also take KT-66, KT-88, 6550C, KT90 and KT-99 in the output stage and 12AY7 and 12AX7 for gain/phase. Any tube replacement that will provide more extension?

Thank you in advance
Siemens 7308 or Amperex 7308 tubes in my preamp (First Sound)
provide the best high frequency extension and overall dynamics from top to bottom. You might try these in your AI L-1.
It's hard to believe that the tubes would limit HF response...after all tubes are (or were) used for RF amplification. In a tube power amp the output transformer is the component that limits HF response, and a large amount of feedback around the transformer (often provided by dedicated windings connected to secondary grids of the output tubes) is necessary to provide flat response over the generally-accepted audio range. If your amp is a "low feedback" design the trade-off is limited frequency response.

Also, why not try a supertweeter? It could be your speakers. Or your ageing ears.
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?

I am running Green Mountain Europa's. Eldartford, the amps are zero feedback design. Hey, I'm 39 and holding, not that old!

Try substituting another preamp.The AIs are good,but high frequency reproduction is not their forte,Transcendent GG,Placette passive/active,First Sound Deluxe, even a CJ.Arrange some home auditions with a cooperative dealer.Happy hunting.
Give it a few more yrs Matty and you'll feel time is passing you by!

Mattybumpkin...If amplification is the problem I really think the power amp is probably the place to look. EL34 and KT88 tubes are pentodes, and I bet that there is local feedback from the transformer to the output tubes. "Zero Feedback" probably refers to "global" feedback.

I suggest that you try a SS amp, or one of a few tube amps that are flat to 100KHz (but these are not low feedback).

For some things, 39 is over the hill.
If you dont have some,try some silver speakers cables.
Construct a time machine and go back to your teens; preferably female.
Buy the Rives audio test-tone CD and run some upper end tests. You'll (probably) cry yourself to sleep for a week.
Check out conversations with your parents; that's what your hearing is going to turn into.
Get your ears cleaned professionaly once a year.
Unless your age starts with a 1 or maybe a 2, 15kHZ is probably a long distant memory. And 10k ain't that far off.
Most of the above advice is useless, unless you first determine what *your hearing is capable of, before what your *system is capable of.
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...
Trelja...While I cannot disagree with your preference for low (or zero) feedback amps, I have difficulty believing that the difference you hear derives from greater bandwidth. Reduction of feedback will change the sound so that it reflects the characteristics of the amplifier, (most likely the output transformer) rather than the input signal. I would expect the bandwidth to be less with low feedback, and this may emphasize harmonics in the 12 to 18 KHz range that you may find pleasing.
The ability to vary the feedback is interesting. Do you have, or can you generate frequency response plots for various degrees of feedback?

Also, is the amp really "zero" feedback? No local feedback around stages, or "ultralinear" transformer windings driving output tube grids?

A schematic would be nice.
Mattybumpkin...A word of encouragement!

You, like eveyone else, have lost, or will lose high frequency hearing. When tests are run, (at least on me) sine waves of various frequencies are used. I cannot hear a sine wave much over 10 or 12 KHz, but I can clearly detect the action of a supertweeter or a filter operating up around 20KHz. My theory to explain this is that the ear senses rate of change of pressure as well as pressure change, and the steep wavefront of the HF sound is sensed, even if the frequency is not. Hey..it works for me.

Also, loss of HF hearing does not, at least for me, affect spatial perception, eg: imaging.
Thank you everyone for the responses.

I am sure my hearing is still good even though from reading the posts here it sounds like I have one foot in the grave. Who should I leave my rig to in my will?

I think I will begin to roll some tubes in the amp first, and if that still doesn't float my boat maybe I will try another pre.

Trelja, I would be curious to hear your impressions of the EL34 tubes you just got. I was thinking of trying the EH EL34's, supposed to have more sparkle up top. I know the comments you mention about the Cary V12 and the attempts to use the other tubes like KT88, etc. I wonder though, the Six Pac's are different circuitry than the V12I that was mentioned in the other thread. The new V12R is supposed to be the same pretty much as the Six Pacs. I wonder if this would make the outcome different. I'll ask Dennis I guess, or Kevin at Upscale. KT88's are more extended than EL34's, yes?


Tvad, I did roll back into the AI L-1 some EH 6922 that I had. It did provide some extension. Thank you. I may try to hunt down a pair of the Siemens you mentioned.

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!
Murata supertweeters. 15k - 100k Hz, no crossover.
Mattybumpkin, I suspect you will notice a difference between Siemens and EH 6922 tubes, and the Siemens 7308 tubes are even better than the 6922 tubes. Try to find some vintage early 1960's Siemens 7308 if you can.