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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
mattybumpkin
eldartford
4,262 posts
 
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.
trelja
3,223 posts
 
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?
mattybumpkin OP
590 posts
 
Trejla,

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

Thnx,
tpsonic
1,092 posts
 
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.
eldartford
4,262 posts
 
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.
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