[OctavianH]

As a fellow Elise owner I appreciate your findings, @OctavianH. I just completed a very time consuming endeavor related to my profession, and am a bit behind all of you "high rollers." Still burning in my Tung Sol 7581A'a in the power position driven by Tung Sol 6SN7GTB's, perhaps 100 hours on the 7581A's. Quite a lot to like with this current combo.,, and I also have a pair of NOS Sylvania 1952 6SN7GT's arriving next week. Depending upon the results with those "bad boys" driving the 7581A's, I'll likely order 2 more adapters from Deyan and switch the 7581A's into the driver's seat. I listen to more classical and acoustic music (just a smattering of classic rock) and am still debating if I follow your route with KT66 powers or bypass that step straight to KT88's. Decisions, decisions!

You can wait until next week when more users will have KT88 in place and decide later, based on their feedback, on which way to go.

 

[DecentLevi]

I got another original GEC KT66 today. I handpicked it to match, which I now confirm fixes the imbalance and distortion of the previous pair on a conventional 1-tube-per-socket setup. Thought I'd do some more comparisons now that we're properly in business.

EL39 vs. GEC KT66 powers shootout

• EL39 as powers: more extended FR with deeper sub-bass, treble is more smooth and liquid, better imaging / instrument separation and PRaT
• GEC KT66 more of a robust, in your face sound slightly more mid-centric by contrast. Soundstage is bigger, but at the expense of much of the instrument separation and expense of some of the titanic realism of the EL39's.
  
  Overall the EL39's have that special x-factor that cannot be duplicated, a 3D lifelike sound that extends wide from top to bottom, better treble quality, deeper bass and far more technically proficient at presenting individual layers of the recording (allowing each instrument to have its' own special voice in the recording). OTOH the KT66's still have their place, with a special vivid robust presentation that may actually work better for some recordings. I do say they compliment eachother well too.
  
  Do note that this was with original GEC KT66's tested and in mint condition from trusted distributor Langrex in the UK. One was burned in about 150 hours and the other was fairly new, and the EL39's had about 400 hours. So unless Genalex is even better than the original design, I'd strongly recommend those interested in the KT66's to hold onto your sacred EL39's if you have 'em. Disclaimer: I've yet to try the Genalex KT66 so YMMV, and YMMV based on preferences. However I do recon the tables may turn a bit with the KT88. Also to be fair, the GEC KT66 is still a goliath tube, leaping beyond many dozens that came before it nevertheless.

KT66 powers with drivers EL12 Spez vs. Valvo EL11 vs. EL39

EL12 Spez sounds glorious as drivers - smooth, extended on both sides and actually not bright. EL39 sounds fantastic as driver - organic, more extended with deeper lows, but PRaT / dynamics are a nuance behind. Valvo EL11 for some reason seems a non-starter with KT66 as powers, sounding a bit flat and non-synergistic.

My top recommendations:
1. EL39 + Valvo EL11
2. KT66 + EL12 Spez
3. KT66 + RCA 6N7 metal tubes

 

[barontan2418]

I too am running a bit behind on the KT front however H1's combination of EL39 and KT66 as powers driven by Tung sol 7581's is certainly a combination made in heaven. I have found myself getting ahead of myself so will hold off on any other purchases (KT88) until all tubes are well run in and perhaps another tube fills the top spot. Have to admit I do have a further two KT66's on the way. My Elise is running on EL39's and black mesh Telefunken EL 11's and with my T1, Arturo Sandoval's Trumpet Evolution has never sounded to good.

 

[DecentLevi]

arcing Sylvania 6080

EL32


EL3N


EL38


EL12 Spez

KT66

EL39

 

[hypnos1]

As a fellow Elise owner I appreciate your findings, @OctavianH. I just completed a very time consuming endeavor related to my profession, and am a bit behind all of you "high rollers." Still burning in my Tung Sol 7581A'a in the power position driven by Tung Sol 6SN7GTB's, perhaps 100 hours on the 7581A's. Quite a lot to like with this current combo.,, and I also have a pair of NOS Sylvania 1952 6SN7GT's arriving next week. Depending upon the results with those "bad boys" driving the 7581A's, I'll likely order 2 more adapters from Deyan and switch the 7581A's into the driver's seat. I listen to more classical and acoustic music (just a smattering of classic rock) and am still debating if I follow your route with KT66 powers or bypass that step straight to KT88's. Decisions, decisions!

Hi LW...classical, acoustic, folk (Clannad etc.) and light rock/mixed (ELO/Mike Oldfield/Andreas Vollenweider etc.) are mostly my cup of tea, and despite being very impressed by the different combinations of 7581A/EL39/KT66, I personally find that none of them can now match the combo of Gold Lion KT66s driving GL KT88s...they were simply made for each other, and I'm sure is a trick missed by the 6L6/KT fraternity who have used them purely as power tubes (from what I can see lol ).

So if funds permit, I can only recommend you bite the bullet and give this combo a try......CJ

 

[hypnos1]

I too am running a bit behind on the KT front however H1's combination of EL39 and KT66 as powers driven by Tung sol 7581's is certainly a combination made in heaven. I have found myself getting ahead of myself so will hold off on any other purchases (KT88) until all tubes are well run in and perhaps another tube fills the top spot. Have to admit I do have a further two KT66's on the way. My Elise is running on EL39's and black mesh Telefunken EL 11's and with my T1, Arturo Sandoval's Trumpet Evolution has never sounded to good.

Hi bt...yo, the 7581A/EL39/KT66 sure is one combo hard to beat...but as I have mentioned just now and again (!! ), even this is surpassed (unbelievably) by the KT66/KT88 combo - as per my own findings as well as @Scutey 's (re. the 88 anyway at the moment) so far. But as usual YMMV lol ...ENJOY!...CJ

 

[connieflyer]

Well I must say as impressed as I was with the Gold Aero 6SN7GT as drivers with KT 66 as powers, have been using the Sylvania VT231's the 1947 version, very sought after today, this tube combo opens up the sound stage even more, vocals are stronger and signal a little stronger. Very pleased with results with 6SN7GT's, tomorrow, I will be using the KenRad 6SN7GT Black 1944 edition and expect more bass and slightly less top end. With these KT66, it seems all bets are off though.

 

[LoryWiv]

You can wait until next week when more users will have KT88 in place and decide later, based on their feedback, on which way to go.

Excellent advice, @OctavianH. I don't want to race too fast forward and miss the journey, although with wise and trusted gurus such as @hypnos1 shining that inviting beacon from the horizon ahead it is tempting. One combo. I've not yet seen impressions on is the GL KT88 driven by TS 7581A. Perhaps I'll try those next if the Sylvania NOS 6SN7GT's don't stop me blissfully in my tracks. Then I can move on to KT66's as drivers as needed. I do feel like the (American) football quarterback marching steadily down the field only to find the goalposts have moved. Not complaining, though, this process is a lot of fun and very rewarding.

Hi LW...classical, acoustic, folk (Clannad etc.) and light rock/mixed (ELO/Mike Oldfield/Andreas Vollenweider etc.) are mostly my cup of tea, and despite being very impressed by the different combinations of 7581A/EL39/KT66, I personally find that none of them can now match the combo of Gold Lion KT66s driving GL KT88s...they were simply made for each other, and I'm sure is a trick missed by the 6L6/KT fraternity who have used them purely as power tubes (from what I can see lol ).

So if funds permit, I can only recommend you bite the bullet and give this combo a try......CJ

Thank you, @hypnos1. Per above I think I have my path mapped out, and likely will include the combo. you are getting such joy from. Your enthusiasm and pure delight for our amps and the options to help them bring out their best is inspiring, I look forward to your jolly posts daily which are both informative and fun!

 

[Scutey]

Excellent advice, @OctavianH. I don't want to race too fast forward and miss the journey, although with wise and trusted gurus such as @hypnos1 shining that inviting beacon from the horizon ahead it is tempting. One combo. I've not yet seen impressions on is the GL KT88 driven by TS 7581A. Perhaps I'll try those next if the Sylvania NOS 6SN7GT's don't stop me blissfully in my tracks. Then I can move on to KT66's as drivers as needed. I do feel like the (American) football quarterback marching steadily down the field only to find the goalposts have moved. Not complaining, though, this process is a lot of fun and very rewarding.

@LoryWiv I have the Elise as well as Euphoria, and will probably have a go with GL KT88 driven by 7581A in Elise tomorrow so give me a day or two and I will give you my impressions if you are interested, it will also be well worth waiting for @OctavianH impressions as well as you can trust his judgement on tube rolling.

 

[LoryWiv]

@LoryWiv I have the Elise as well as Euphoria, and will probably have a go with GL KT88 driven by 7581A in Elise tomorrow so give me a day or two and I will give you my impressions if you are interested, it will also be well worth waiting for @OctavianH impressions as well as you can trust his judgement on tube rolling.

Perfect, I appreciate that and look forward to your impressions, @Scutey as well as the continuing input from @OctavianH et al.

 

[Johnnysound]

I got another original GEC KT66 today. I handpicked it to match, which I now confirm fixes the imbalance and distortion of the previous pair on a conventional 1-tube-per-socket setup. Thought I'd do some more comparisons now that we're properly in business.

EL39 vs. GEC KT66 powers shootout

• EL39 as powers: more extended FR with deeper sub-bass, treble is more smooth and liquid, better imaging / instrument separation and PRaT
• GEC KT66 more of a robust, in your face sound slightly more mid-centric by contrast. Soundstage is bigger, but at the expense of much of the instrument separation and expense of some of the titanic realism of the EL39's.
  
  Overall the EL39's have that special x-factor that cannot be duplicated, a 3D lifelike sound that extends wide from top to bottom, better treble quality, deeper bass and far more technically proficient at presenting individual layers of the recording (allowing each instrument to have its' own special voice in the recording). OTOH the KT66's still have their place, with a special vivid robust presentation that may actually work better for some recordings. I do say they compliment eachother well too.
  
  Do note that this was with original GEC KT66's tested and in mint condition from trusted distributor Langrex in the UK. One was burned in about 150 hours and the other was fairly new, and the EL39's had about 400 hours. So unless Genalex is even better than the original design, I'd strongly recommend those interested in the KT66's to hold onto your sacred EL39's if you have 'em. Disclaimer: I've yet to try the Genalex KT66 so YMMV, and YMMV based on preferences. However I do recon the tables may turn a bit with the KT88. Also to be fair, the GEC KT66 is still a goliath tube, leaping beyond many dozens that came before it nevertheless.

KT66 powers with drivers EL12 Spez vs. Valvo EL11 vs. EL39

EL12 Spez sounds glorious as drivers - smooth, extended on both sides and actually not bright. EL39 sounds fantastic as driver - organic, more extended with deeper lows, but PRaT / dynamics are a nuance behind. Valvo EL11 for some reason seems a non-starter with KT66 as powers, sounding a bit flat and non-synergistic.

My top recommendations:
1. EL39 + Valvo EL11
2. KT66 + EL12 Spez
3. KT66 + RCA 6N7 metal tubes

Wow DL ! Do you mean you are using original, NOS, GEC KT66 ? Well, those pieces cost a lot of money...dark or clear glass ? By all accounts the new Genalex are “close” to the sound of the clear glass originals...but not quite equal. The “x factor” that you mentioned. In my experience, good reproductions of “classic” tubes tend to sound a bit clearer, extended and not “mid centric”, but are less holographic and natural sounding than the originals.

Absolutely agreed with your choice of EL39/Valvo EL11 as a top combo. Above all, there is great synergy here, (don’t know why, but the tubes are made one for the other)...and the intensely deep insight into the music of this combo, with a fully burned-in pair of EL39s is admirable. Do not have KT66s yet for comparison, but certainly KT77s sound great as powers in Euforia with a vibrant, open sound...and even better as drivers of the EL39s !! The mix of a “new” tube with a “classic” one gives a different sound perspective: nice dynamics, full detail, extended highs, bass and the sweetness of the classic...however, with the Valvo EL11s the combo sounds more refined and holographic.

In my system, of course (Lol). I recently totally “germanized” my power amp with TFK drivers and RFT EL12N powers, (EL12 spez soon) to (hopefully) increase linearity, neutrality...and the piece is now, well, very “fast” sounding, delivering the tightest, most precise and “bouncy” bass ever. And not only the bass: the music flows with such a clarity, purity and definition as to sound above all the power amp tubes that I know of, save perhaps for the EL39s, (with a very different, “darker” presentation). I am hooked with this sound. The EL12Ns are wholly different animals as power pentodes than as triodes in Euforia...I allways liked their transparency, but at full heat they really awake and deliver the goods. Anyway, now the amp is not “euphonic” at all, maybe analytic with just a trace of “warmth”...Euforia (preamp) loves it, and well, a combo such as EL39/EL11 balances the sound beautifully...

 

[DecentLevi]

Wow DL ! Do you mean you are using original, NOS, GEC KT66 ? Well, those pieces cost a lot of money...dark or clear glass ? By all accounts the new Genalex are “close” to the sound of the clear glass originals...but not quite equal. The “x factor” that you mentioned. In my experience, good reproductions of “classic” tubes tend to sound a bit clearer, extended and not “mid centric”, but are less holographic and natural sounding than the originals.

Absolutely agreed with your choice of EL39/Valvo EL11 as a top combo. Above all, there is great synergy here, (don’t know why, but the tubes are made one for the other)...and the intensely deep insight into the music of this combo, with a fully burned-in pair of EL39s is admirable. Do not have KT66s yet for comparison, but certainly KT77s sound great as powers in Euforia with a vibrant, open sound...and even better as drivers of the EL39s !! The mix of a “new” tube with a “classic” one gives a different sound perspective: nice dynamics, full detail, extended highs, bass and the sweetness of the classic...however, with the Valvo EL11s the combo sounds more refined and holographic.

In my system, of course (Lol). I recently totally “germanized” my power amp with TFK drivers and RFT EL12N powers, (EL12 spez soon) to (hopefully) increase linearity, neutrality...and the piece is now, well, blazingly fast, delivering the tightest, most precise and “bouncy” bass ever. I am hooked with this sound. The EL12Ns are wholly different animals as full power pentodes than as triodes in Euforia...I allways liked their transparency, but at full heat they really awake and deliver the goods. Anyway, now the amp is not “euphonic” at all, maybe analytic with just a trace of “warmth”...Euforia (preamp) loves it, and well, a combo such as EL39/EL11 balances the sound beautifully...

Yup these were mine above, except I replaced the one on the right with one that matched better. About $450 for both including shipping. I got these for my upcoming amp before I even knew of the Genalex, but I prefer the finest things when possible. (who knows maybe Genalex KT66 are better). The signature is definitely not mid-centric; however when put against the EL39 it did give me the impression leaning that direction. I really prefer the EL39 on the Euforia, but YMMV based on preference, tube condition and things could be different on another amp. The KT77's sound like a top performer from your words too, and it looks like most of those are new production.

 

[OctavianH]

Around 30 hours here, and I had "ups" and "downs" regarding the sound quality but now everything seems more stable.

I have a feeling that the glow increased in intensity, even if this does not make too much sense, but anyway these are beautiful in the dark:

I wonder if they will continue to improve, and how much. Anyway, for the lucky ones who own or ordered original GEC / Osram / other vintage KT66 / KT88 please share your impressions. I start to look more and more to this box:

Ebay Link here:
https://www.ebay.co.uk/itm/16-x-GEC...566814?hash=item1cdbe9091e:g:FtQAAOSw7qRdrtNZ

Too bad we are adults and Santa does not come to us anymore. I would not refuse such a gift

 

[mordy]

You have to ask h1 to help you if you want them - the seller only wants to sell them in the UK and prefers local pick-up.

 

[OctavianH]

I just look at them, I am not willing to spend 2500 EUR at the moment for those. At least not before I will try the Genalex new production KT88 and discuss with people who own both new/old ones and can make a comparison.