Isaac7 wrote "New Russian TungSol 7581a tubes slightly improved on the things that were important to me. a little better bass, little better guitar tone. Plus I felt comfortable using the 5ar4 with them for a bit more power. "

I haven't listened to the new 7581a tubes but four highly respected amp builders have told me that they love them. That they equal the quality of vintage 6L6GC and 7581a. Dave Gillespie has tested them and found that they meet all power specs and have very low distortion.

I have two quads of the new Genalex Gold Lion KT66, which are made in the same Russian factory but which are different. The GL KT66 draws 1.3A whereas the 7581a draws 0.9A and the internal construction differs.

I like the KT66 in my KT88 HO amp and even more in my PSE.

I would like to try the 7581a for at least a few minutes in my PSE to compare against the GL KT66, but I'm reluctant to drop $100+ for a quad when I'm not sure I would even like them as much.

Two people who have tried them all say that the new Tung-sol 7581a, KT66 (also 0.9A in the Tung-sol glass), and 6L6GC-STR all sound very similar.

Yeah, I started this thread because I think a lot of good info is buried in the monster thread. Ideally we’d have different threads for different topics so people can find the info they want.

The performance we get out of any particular tube will vary considerably with the load it sees and how loud you play. My phase tech PC 3.5 speakers sound like they are more sensitive than yours. Then again I rarely ever go above 82 db and I sit around 7 feet from my speakers so maybe I just don’t need as much juice. Which speakers do you use?

I have Von Schweikert tower speakers, which are essentially their old VR-7 model, but a bit customized by the original designer. They are 90-91 db. I sit 7' from them. Usually listen at 75-80 db, sometimes a bit louder.

Their strengths are throwing up a very large, transparent soundstage with a neutral overall balance. I've come to really appreciate the big image and so gravitate towards tubes & components which do the same. Likewise for the neutral bass, no measurable mid-bass hump at all. So any change which adds mid-bass warmth sounds tubby to me.

Likewise the highs are also neutral, no roll off. Some might find them too bright. So any tube combination which adds brightness starts to sound harsh to me. This has been the case for a number of tubes.

Interesting, my speakers are supposed to be around the same sensitivity. I'm guessing there is quite a bit of difference when it comes to the loads the amps see vs. frequency. I say that because I didn't find the KT88 tubes to offer me very deep bass, or at least not like I can get with other tubes.

Evaluating my output tubes on deep bass, for extension, definition and volume the KT88, KT120 and KT150 are the best in both my KT88 HO and PSE amps. I have some cuts with very low piano and string bass notes and I listen to hear the strings vibrating, clarity and fullness. With some tubes these passages the strings sound fuzzier and rolled off. With some tubes the higher mid-bass notes are overly prominent, tubby and forward.

My speakers have dual 9" woofers and go down strong to 32Hz with some output down into the low 20s.

My SS amps are even better on deep bass, going down deep with even better dynamics and definition. I don't consider deep bass to be the forte of a SE tube amp. I am satisfied if the SE amp can be reasonably good on bass while producing a glorious midrange and big, open natural presentation.

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My speakers can get down to 40hz or so. I agree with leaning into the strengths of SE amps. Right now all I have is the one amp though lol. So when one set of tubes gives me better bass I notice. Some of the other combos have been amazing for things like classical guitar but when I want to rock a bit I want to feel the bass.

Now that I have a preamp I like I anticipate getting a solid state amp too. We'll see how much I use it and for what. What a hobby...

I have been enjoying the Firebottle KT88 with 6v6 tubes. I have gone back to my old standby of the tall bottle 7n7. I had been running it with an RCA 5u4g but the other night I noticed a dull orange glow on the plates. Yikes! I have since started using a 5Y3 rectifier and that has taken care of the glowing plates. I haven't noticed a difference in the sound either. Listening in the dark is also a good diagnostic for amp operation!

I have dug up a tall Sylvania JAN 6sl7gt with the getter flashing in the bottom. This along with the Sylvania 6sl7wgt are my favorite tubes to go with the 6ar6/807. I will try the JAN 6sl7 with the 7c5 tubes next week but I think it's going to be a winning combo as well. I am using a passive preamp so maybe the extra gain is an advantage in my system.

I would encourage you to not assume all 6sl7 tubes sound the same, not even the Sylvania ones! I had previously used a tall 7f7 which is equivalent to the tall, completely chromed Sylvania 6sl7. The 7f7 felt a little hard and ended up being fatiguing. That surprised me because the 7f7 seems to have the same round plate construction as the JAN 6sl7gt. Both the brown base 6sl7wgt and the tall JAN 6sl7gt are much smoother. I think the tall JAN 6sl7 edges out the other one in both bass and overall tonal rightness. I guess it could just be the difference between these two particular tubes. In any case, both of these are widely available for reasonable prices and are worth trying.

New power tubes! My friend sent me some 6ez5 Sylvania tubes. They are supposed to be drop in replacements for 6v6 tubes. I'm now using an active preamp so my comparisons with previously used tubes are not going to be completely comparable but these seem to be noticeably warmer than the Sylvania 7c5 (6v6). I'm using the Sylvania tall bottle JAN 6sl7 and the tone is delicious. I dare say this combo is giving me the prototypical "tube sound" of being warm and a slightly loose bottom end. Guitars, acoustic or electric, sound amazing as does piano. Bass heavy music can get a little wooly.

Interestingly I can use these with a 5u4g rectifier without getting the orange glow like I was with the 7c5. You can get these tubes for $5 a piece, well worth it!