12ax7 vs 5751


hi all,
i need some advice. i`m very new to tube amplifiers and i`ve been doing some tube rolling.

i currently have a pair of grant fidelity matched psvane 12ax7t`s in my amp which sound fantastic.

what i`d like to know is which are the better tubes, 12ax7`s or 5751 tubes. i`ve been looking at forums and there are folk out there that say 5751 tubes are better than 12ax7 tubes.

can i have your thoughts on this please and also which are the good 5751`s to go for.

i really like the psvanes but if they can be bettered i`d go for it as my next line up of replacement tubes.

my amp is a yaqin mc100b. the tubes i have installed at the moment are.....
2 x psvane 12ax7t`s
2 x brimar 6sn7gty/cv1988`s
2 x sylvania 6sn7gtb`s
4 x electro harmonix kt88eh`s

many thanks in advance guys.
grayf
Last the Ei KT90's used to be my least favorite output tubes. Only after swapping out the drivers (2 Rca 12at7wa and input 1 Sovtek 12ax7) with Gec CV6091 (military version of the A2900) and Rca triple mica black plate 5751 did I really start to like the Ei's. So I believe with the right combination of tubes anything can be made to sound better :).
So have fun
Grayf
It is good to hear someone enjoying the process instead of simply obsessing...
Are the Telefunken12ax7s just a standard issue or do they have different ones?
I have tried 7025s only briefly. I found them to lack the delicacy transparency and detail the 5751s gave me. I didn't try many because they seem to be a favorite of the Guitar amp guys who drive up price and make good ones quite scarce. I know I tried RCA but don't recall others. The major differences in Telefunkens are smooth vs ribbed plate and early vs later. Also the holy grail of 12AX7s is the ECC803S by TFKN. I own some 802 and 801S but sadly never lucked into or afforded the 803S.The early smooth plate 12AX7s seem to be the preferred tube but not by everyone.
ok the telefunkens i have are the ecc83 smooth long plates with halo getters. no idea what year they are and they have the diamond stamp underneath. i did look into those ecc803s but they were pretty much out of my price range, but yes i`ve read that they are the best ones to go for, but i think the telefunken ecc83 are more than good enough. the ecc803s are much harder to find too. there`s a pair on ebay i`m watching just to see how much they go for. the difference in sound from the smooth plates and ribbed plates are supposed to be.....smooth plates = accurate sounding, ribbed plates = warm sounding. i opted for the smooth plates because the black treasure kt88-z`s that i have on order are warm sounding and i don`t want an overly warm sound from my amplifier. the sound i`m getting at the moment is accurate with a hint of warmth which i`m loving.

i had more of a listen earlier. listened to adele and also steve hillage "green". adeles voice sounds very natural. her voice has a natural dryness which the telefunkens preserve perfectly and some of her tracks have amazing bass drive. those tracks are extremely pleasing to listen too as i`m sure my neighbours can vouch for the bass!!!

listening to steve hillages green cd is just amazing. the highs are so extended. more so than the ei elites! there`s only one track on green that i don`t really like that much (too hippyish lol) but at the end of the track the last 30 to 40 seconds there are some mindblowing high frequency sounds, well these telefunkens produce these highs with such beauty and accuracy. it literally makes your eyes widen in sheer surprise and awe! these high frequency synthesiser notes hang amazingly in the soundstage and actually move around and these tubes make it so easy to follow. i think magical is the word i`m looking for.

onto dave gilmours cd on an island. on this disc he wrote a song called smile, a very poignant song about loved ones lost. without going into it i lost family members between 2005 and 2007 as well as having to have my dog put to sleep. these tubes bring out all the emotion and i couldn`t help but blub big time! this is probably the most beautiful track i know on any cd with beautiful lyrics that will help anyone who`s been bereaved come to terms with their lost ones. thank you mr gilmour for that! my favourite track on this cd is the very last track called "where we start", and oh my god the guitar tones are just so seductive now and to die for!!! i just cannot stop listening to this track and i bet the neighbours know every last second of this track lol. the sound effects all the way through this cd are just so clever and amazing to listen to. i recommend this cd to all. i think it`s his best work ever but thats my opinion and i must admit i have emotional ties to this cd.

in a way, as much fun as this has been with tube rolling i`m so looking forward to concentrating on the music. thats not far away now. i am a little wound up with the length of time i`ve had to wait for the ge 5751`s and the black treasure kt88-z`s but i`m sure the wait will be worth it. (i gotta learn to be patient lol)

the ecc83`s that i have here are more than good enough!
god there`s always something i fotget to add which is always important too lol. the noise floor. it`s lower on these tubes than the ei elites which is low enough as it is. it makes for a super impressive listen. hard to describe too. it`s like notes are produced from darkness. this is an aspect that i just love. it`s also the very reason i`ve ordered the black treasure kt88-z`s. these are supposed to have that in spades! another reason why i`m wound up with all the waiting lol. i did warn my postman earlier when signing for the telefunkens lol. told him not to deliver anymore post unless he has my parcels lol. he thinks i was joking!!! muwaaaah ha ha ha lol
a quickie update, i contacted the shop in hong kong about my kt88-z`s. they should be here next tuesday. customs have my tubes and have just released them. they had them ages too grrrr! no sign of my ge 5751`s though but to be fair it states in their advert it`ll take 20 to 25 days so hopefully they`ll be here next week too
I have not read every post in this thread, so I will apologize ahead of time if I am repeating any previous comments.

I have Rogue M180 monoblocks that for a year or so I used with Silverline SR17.5 bookshelf speakers. I used the 5751 with them and it was great. I eventually acquired some Silverline Bolero floorstanding speakers and the 5751 didn't work well with them at all. The sound was just, well, blah. I replaced the 5751 with a Telefunken rib plate 12AX7 and the system was dramatically improved. With that substitution the tube compliment in my amps was Telefunken rib plate in the 12AX7 signal tube position, RCA 12AU7 tubes in the driver position. I have since replaced the RCAs with Telefunken rib plate 12AU7s.

I also have a pair of Telefunken smooth plate 12AX7s. I put them in the signal tube position and both me and a buddy noticed that the leading and trailing edges of transients were slightly smeared compared to the rib plate. I prefer Telefunken to all other tubes I have auditioned and/or used in my system (the others being RCA, Tung Sol, Amperex). But to me the smooth plate Telefunken is slightly warmer than the rib plate. Both are very, very clear, but I preferred the dynamics and crispness of the rib plate, and once they break in, mine were NOS, they are actually quite sweet. Smooth, clear, dynamic, fast.

Also, in my headphone amp I have a smooth plate 12AX7 and smooth plate EL84s, but I plan to replace the 12AX7 with a rib plate - it's on order and should be here soon. We'll see how that goes, in that application the smooth plate may be the ticket!

Anyway, back to the original question, I think the 5751 is a great tube, but I've been very happy since moving on to the Telefunkens.
Reynolds
When you say "the leading and trailing edges of transients were slightly smeared"...
Does that mean the high frequency is smoothed out? Sorry if the ? seems silly but I have Focals and they seem to be a bit on the bright side, just wondering if tube change has the potential to balance that out a bit. Of course much of the sound depends on the recording.
i did some rolling to and forth between the ei elites and the telefunkens today. there really isn`t much if anything between them. the telefunkens definately have a wider soundstage. the sound seems to go beyond the speakers which i really like but in pretty much all other area`s i couldn`t really tell the difference. the ei elites, one side is slightly microphonic but again it doesn`t really effect the sound performance at all.

i have my pioneer bluray player plumbed into the amplifier and watched shrek earlier. the sound was really good. music scores in the film sound excellent and voices throughout the film sound very natural. of course there`s no explosions or the like in this film so i can`t comment on stuff like that plus i have to think of the neighbours! music on this film certainly has some punch though!

by the way i`m from the uk and had our first snow fall today! i`m praying it stays for at least some of the week so i don`t have to go to work lol more listening time for me hopefully!
Mcpherson,

No worries, it's certainly not a silly question. I'm not confident that I can answer your question about the brightness of your system to total certainty, but I can perhaps explain my earlier comments a little more clearly.

I want to make sure that my comment about the slight smearing is in the proper context. I was comparing Telefunken rib plate 12AX7 to Telefunken smooth plate 12AX7 in the signal tube position of my Rogue M180. The driver tubes were held constant with Telefunken rib plate 12AU7. The Telefunken were already my favorite tubes for detail, dynamics, speed, tone, and certainly clarity. The comparison between the smooth and rib plate is really getting down into the small details, I like either one better than anything else I've had in my system, and I could live happily with either of them and never look back.

We were listening to acoustic guitar with the rib plate 12AX7 first, then swapped it out for the smooth plate. After a few moments we realized that a little bit of information had been lost in the sound of the strings in the trailing edge of the notes. At the edges of these notes the rib plate was more convincing, the smooth plate just very slightly fuzzy. But as I mentioned before, I could live happily with the smooth plates.

I think the rib plates have a smooth sound, which to me means the sound isn't edgy. I just think rib plates provide a little more musical information around the edges of notes than the smooth. I was on another thread where the discussion included RCA tubes (which I used before moving to Telefunken) and one someone commented that Telefunkens were a little brighter sounding than RCA, so perhaps changing tubes could help you. I moved to Telefunken because I was hearing dynamics and clarity. I've never had to battle brightness in my system, and I made the change too long ago to remember that aspect of the RCA sound. But along those lines, RCA is warmer than Telefunken, and Mullard is warmer than RCA. If the other Audiogon member's comment is indeed correct, then maybe changing tubes could solve the problem of brightness in your system.

You didn't mention anything about the rest of your system other than the Focal speakers - do they have beryllium tweeters?

I asked the guys at the stereo shop today about your questions. Several comments were made, but there wasn't too much discussion, so I'll just relay the comments: (1) Focal are bright sounding speakers, (2) yes, it is possible to reduce brightness with a change in tubes, but they would need to know more about what is in your system, (3) would first be looking at your interconnects or speaker cables, (4) wondered if you had silver cabling in your system as that can sometimes add brightness.

As far as tube microphonics, if you google “tube microphonics” you'll get plenty of hits. But you don't want any microphonic tubes in your system. I had a very microphonic tube in my preamp once and just touching the volume knob was amplified through the speakers.
i have a bus route that goes straight past where i live and the road is uneven a little. when the bus goes over the uneveness my flat shudders! one of the tubes picks this up but its onlt very slight and you have to be pretty close to the speaker to hear it. it`s like the tube is vibrating. i tell you something that helps in this case is using sorbothane feet under the amp but my amplifier is pretty heavy (30 kilo`s) and i think i`ll need to purchase extra sorbothane feet. they`re very cheap and you can get them off ebay. i have them under my cd player and my bluray player too. amazingly they made a difference to the picture on my bluray player. don`t ask me how but the picture is sharper. i thought it was me but everyone thats been around here has noticed the difference too! they helped under my cd player too with the soundstage. it just seems more focused. not bad for a cheap upgrade! if i didn`t have them under the amplifier i`m pretty sure it`d be a nightmare to listen to. not sure if those tube dampers work. i might give them a go unless anyone reading this can advise otherwise.
Mcpherson please feel free to ask any question you wish ok. if i can`t help then i`m very sure others will like reynolds for instance. like you i`m a newbie to tubes aswell so any information is valuable. tubes are expensive enough without making costly mistakes. all the tubes in my amplifier are in there for a reason. i`ve done endless research on each tube as to what their sound characteristics are and kind of gambled buying them. i`ve been very lucky so far in my mixing and matching and each tube i`ve added has enhanced the sound out of my amplifier. my treasure tubes kt88-z`s look like being delayed further now because of this snow as probably will the ge 5751`s aswell :( i`m dying to fit them all in!!!
Grayf, first, I'm happy for you that you are having a good time tube rolling, learning, listening and so forth; but, I have a small piece of advise, be careful where you buy tubes from. For example, on Audiogon there are some excellent tube sellers with stellar reputations and had you bought those KT88s from say, Trelja, Grant Fidelity, Jim McShane or some others, you would have been enjoying them for weeks already, be careful my friend, so far it seems like you have had good luck. In the UK, Watson sells very good tubes among others. Best.
Reynolds
My system is:
Sony es5400 cdp
Thor ta-1000
H/K Citation 16a (rebuilt to the max) @150wpc
Focal 918s (Not beryllium tweeter)
Transparent IC (entry level I think Link)
Audioquest IC (maybe second step up in their line)
Monster Cable Z series speaker cables

Hopefully some tweaks here and there will warm things up a bit. I really cant complain, I got everything except the Focals within the last 6 months. So I basicly just got started.:)

Thanks guys for answering my previous questions.
hiya mikirob, funny you should say that but before i bought any of the hifi i did a massive amount of research on amplifiers, cd players, speakers, interconnects and speaker wires. the biggest gamble for me was the amplifier. as much as i read on the yaqin mc100b i still couldn`t be 100% sure it was going to be a goodun being so cheap, but there were so many good write ups i decided to take a gamble. if it turned out to be rubbish at least i could re-sell it for roughly the same price as it was secondhand. in a way i think it was good that the tubes were worn and needed replacing. at first i thought i`d made a major mistake because on first power up the pops and crackles coming out of the speakers made me think it was faulty. i decided to get a pair of the psvane 12ax7`s which transformed the sound and it was then i really started researching all the tubes. i then read about grant fidelity and chose to buy his matched psvane 12ax7`s and yes there was a small difference in sound. i then started researching good places to buy tubes from. all the tubes have been from reputed good sellers with the exception of one set and thats the ge 5751`s that i`m currently waiting on. the kt88-z`s are from a good seller in hong kong and because of the length of time it`s taken i sent them a kind of angry email. they got back to me within a couple of hours and they spent that couple of hours investigating exactly where they are. they also sent proof that they were sent on the day they said they were sent. it`s the customs here in my country is where the hold up has been but thankfully they`ve now been released so i`ll get them this week. it`s just bad luck that we now have snow to contend with! i also had a good chat with karl at karltones in my country. what a great guy he is. he spent almost an hour chatting on the phone giving me all kinds of advice and recommendations. i asked him for advice on the telefunkens and ge 5751`s and recommended both even though he stocked neither but i did buy the jan philips 5751`s off him for a nice cheap price. i make sure i always check out the places i`ve bought the tubes off. i remember reading aricles about being weary where you buy tubes off and at the prices they go for i didn`t want to make any mistakes or at leasr cut down on the mistakes. so far it`s all been good. i wont be buying anymore tubes now once i`ve got the kt88-z`s and the ge 5751`s. i think all the tubes i have are more than good enough quality and as for the yaqin amplifier......i`m stunned! i can`t believe how that amplifier has reacted to all the tube changes i`ve made. i also want to pay tribute to all the rest of the equipment i own too. i think the biggest surprise are the speakers. very cheap and they let me hear all the changes i`ve made not only with the tubes but the wires too. i hope and pray the kt88-z`s will be the last piece of this very special jigsaw. i hope anyone else with this yaqin amplifier reads this and the tube selections i`ve made. even as the sound stands now i can imagine i`ll have to spend an exceedingly much larger amount of money to beat this sound. this amplifier is very special indeed. it actually makes me wonder weather or not to bother changing any capacitors in the amp such is the level and quality of sound but we`ll see. i intend to start a new thread on this very subject once i get the tubes i`m waiting on and once they`re run in. i wholeheartedly agree with you on being careful where you buy the tubes from and i really hope others take note of this too
McPherson,

It looks like you have a nice system, but unfortunately components with which I have no experience. My best suggestion, I think, is to find a dealer that will let you take some cables home with you to audition in your system. That's how I got my system dialed-in.

Preamp: if you are using Telefunken, you could maybe try RCA. They are a bit warmer than Telefunken. If you need still yet more warmth, then move to Mullard. Andy Bowman at Vintage Tube Audio sells what he calls Andy's Picks. These are used tubes that he has tested and if you want to do some tube rolling, this is about as economical and safe a way to go about it that I know. I get all of my tubes from Andy and recommend him highly.

Speaker cables and interconnects: Cardas Cross speaker cables are warm and are worth an audition. But again, find a dealer that will let you audition them in your home.

Sorry I couldn't be of more help, but now that you have posted the list of your components, hopefully others with more experience than me will be able to help.

Best regards,

JBS
Reynolds
Thanks for the input brother. I just bought the Thor and it came with the stock Golden Dragon tubes. I am very much looking forward to experimenting with tube rolling. From what I have read, the Modwighted Sony warms up a click or two also.
Mcpherson
I own Focal JM Lab 936 non Berylium tweeter speakers and it took a combination of things to get the tone I wanted. You have to ignore all the negative crap you will read about trying to adjust the tone of your system. In my mind it is my system and I want it to sound the way I like, not the way some one else delares is correct.
The tubes you want to warm up that tweeter is most likely going to be a good old stock 12AX7 Mullards from the 50s or 60s that you put into the pre amp. The Blackburn long plate in particular. I think Brent Jesse at Audiotubes.com may have them. These are warm tubes, but be aware that almost any British tube is going to lean towards the warm side. If you can roll input tubes into the HK again look to Mullard for the best results.
The other things you want to do- although this will cost quite a bit of money- is to get Cardas "Golden" whatever interconnects, I have the Golden Refs. These copper interconnects really make the Focals sound great. I also suggest good copper speaker cables. Again ideally Cardas or Jena Lab but both do cost a lot even used . I would never the less look for them to show up. I lucked into some used Jena Labs and the sound is fabulous.
I happen to have an AE-3 Pre Amp by AES a Cary brand which uses 6SN7s which are delightful tubes for smooth and rich tone, it made a world of difference in my system. Good Luck!
Mechans
Thanks for the information. I am assuming you had a similar impression of the Focal sound as you started tinkering around with tubes and cables?
Grayf I am fairly new to tubes also and enjoy tube rolling a lot. Friday night I had a real big problem. One of my Gec CV6091/A2900's went out and took a Ei KT90 with it (but didn't know it right away). So I replaced the Gec with my Brimar yellow T's and the KT90's with my Tung Sol 6550 black plates. Sat morning I decided to verify the KT90's and sure enough 1 was bad. I didn't know it at the time but when I put the 6550's back in and damn the Brimar took out 1 of my 6550's (all in the same positions). I never thought anything like this could happen. But it did. I have all stock tubes back in now except for my Rca 5751 triple mica black plate. So it was a very sad and more important very expensive weekend for me. I'm still confused because I have had output tubes go before and that was it. Anyhow be careful should an input or driver tube go.
Forgot to mention the lesson I learned is in the future if I have any input or driver tubes go bad to have them checked out with any output tubes in the channel.
Yes, as a general observation, British tubes do deliver a warmer sound. There are makes of other nationalities that will also do the same. For a warmer sound, I like Amperex Bugle Boys (Netherlands). These tend to work reasonably well in all applications.
Yes Mcpherson, I found the Focals very bright and somewhat over analytical when I first bought them. In the store, I was dazzled by all that detail and transparency. Wouldn't you know, it I had auditioned them by letting the store choose the amplification and source, of course it was all tube! Well, I got them and I had a really nice Musical Fidelity SS integrated amp, and was I in for a surprise. It took a complete system overhaul, but I stuck with them tinkering until I got them to sound the way I knew they could. Now they astonish and delight me ever single time I hear them.
I disagree with those who think that any high caliber equipment, when well implemented, works with all speakers. The real trick BTW was the use of tube power amps, not just the tube pre. Together the all tube system is incredible. The quick fix is prolly using Mullard NOS/OS tubes and getting Cardas cabling. However, I almost guarantee that you will find tube power amplification to be the ultimate answer and I bet you will be deeply pleased with the result.
Mechans
What type amp/preamp are you using? I will probably trying to get the Thor amps to compliment the pre once the smoke clears from the preamp purchase. My wife is tolerant but not quite as excited about audio as I am!
I am gonna order a replacement tweeter and then start trying some different tubes and see what happens.
Thanks jayson
hi all,

the ge 5751`s turned up this morning! i gave them a good listen. very clear sounding as if the sound has been polished. very nice sounding bass, quite deep and punchy. there`s not a world of difference between these and the telefunkens. the soundstage is a bit shallower though. listening to dave gilmours guitar on the track "where we begin" is the best tone i`ve yet heard. tone wise these are the best of all the 12ax7 and 5751 tubes BUT i must admit i prefer the depth of the soundstage i get with the telefunkens so it`ll be those that will grace my amplifier from now on! they give me everything i`ve been looking for.

the treasure tubes still haven`t been delivered but they are in the country now. the delays are because of the big freeze thats happening in the united kingdmom and europe so i still have those to listen to yet and i will tube roll the 12ax7`s and 5751`s to see what works best.

i discovered an amazing recording last night too! k.t. tunstalls "eye to the telescope" cd is just about as holographic as you`re ever going to hear. the depth in the soundstage is mindblowing! if you want to show off how good your system images then try this cd, plus she has a dead sexy voice!
Sounds like you are set on the tubes.
If you get rid of the 5751 I may be interested.
I looked up kt tunstall, pretty good. Is the recording quality? Dido kinda fits in that same sound.
My favorite cd since getting the Thor is Commodores anthology even though Im not really a Cs fan. Just sounds great!
I have 2 pairs of 5751 RCA and Sylvania, all test very good. I think they are RCA Triple Mica Black Plate, from 1960's.How much do they go for. I don;t need them, i like the 12ax7 in my VTL 5.5. 1pair RCA 1 pair Sylvania
Thanks for any info
Mcpherson,
Thor has a very very good reputation. If you can get the British tubes into the pre it will make an obvious improvement. I happen to use a highly Modded AE-3 by AES a sub brand of Cary. It is a simple pre which uses 6SN7s, they have great, mellow tone, and are highly linear. It doesn't hurt that I put some very fine, metal base Sylvania 6SN7 "Ws" in it. Thor power amps use EL 34s and would appear to be a really good choice. I have a variant of EL-34s in my power amps, the tetrode 6CA7 fat bottle by EH, which sound really big and powerful. My amps, BTW, are Opera Consonance Cyber 800 monoblocks. The inputs tubes are OS Tung Sol 5687s and Mullard 2493s a 6922 variant. My speaker cables are Jena Labs entry level, which are an all copper braid. The combination is magical.
I have 2 pairs of 5751 RCA and Sylvania, all test very good. I think they are RCA Triple Mica Black Plate, from 1960's.How much do they go for.
I just bought a pair of Rca 5751 triple mica black plates for 70usd. It's my single input tube and I love it. I've read the Sylvania's are supposed to as good but I have no experience with them.
I have Tung-Sol long plate 5751's, GE triple mica black and grey plates, Sylvania gold 3-mica grey plate, 2 mica RCA black plates, and more, but the only 5751/12AX7 slots I have are in my driver board on my power amp. I find that some of the lesser tubes can sound a little stuffy, but all of these that I listed sound pretty damn good. The Tung-Sols seem to be the cheapest (when you can find them), so that's what I use regularly. My driver board is also designed for 5751's; I've found that 12AX7's just don't sound as good in the circuit. I did enjoy 5751's in place of 12AX7's in the guitar amps I used in the past.

Grayf - I got a quad of the treasures in the mail two days ago. I think they sound as good as my NOS Siemens, Svetlanas, and RCA branded mullards fresh out of the box (and apparently there's about a 400 hour break-in window). I think you'll enjoy them.
hi all

i did some extended listening yesterday evening at a much more decent sound level. i found the ge 5751`s a little too warm for my set up. all the detail is there just too warm. my amp is already on the warm side so i guess the ge`s were too much for it. they`re a little noisy too with pops and crackles coming out of the speakers until they`ve warmed up so i`m definately sticking to the telefunkens for now. i will try them again once i get the treasure kt88`s and all the other tubes to see what gives me the best sound.

Mcpherson the k.t. tunstall cd is a very very good recording indeed. it`s the best cd i`ve heard so far and thats saying something! i thought dave gilmours cd was good if not the best but k.t. tunstalls is even better! when i get the treasure kt88`s i`ll have another listen to the ge 5751`s and if they`re still not suitable we can do a deal if you like ok. i got them for $60 but because they`re a little noisy i won`t be asking the same as what i bought them for so at least you`ll be able to see if they`re more suited to your set up without breaking the bank. i thought about your set up when i was listening to them yesterday evening. my amps just too warm to get the magic out of the ge`s.

talking of those kt88 treasure tubes i can`t wait to get them. not looking forward to the lengthy breaking in though but i`m sure they`ll be fun all the same. i`ll do a more in depth review of them too when i first install them right the way through to be broken in. there`s reviews out there for them but nothing much in the way of in depth reviews, so keep dropping by on this thread there`s much more to come guys!
Dear Reynolds853:

I think the rib plates have a smooth sound, which to me means the sound isn't edgy. I just think rib plates provide a little more musical information around the edges of notes than the smooth.

This has also been my experience with Telefunken ribbed v. smooth. I also find the ribbed to be a bit punchier. I prefer them.

Best,
Bill
Ohnwy, yes I have tried (own) 7025's. They can be very good. I particularly liked the Raytheons. Having said that, and with all due respect to some of the comments above, there is no way that one can make a general comment about the superiority or inferiority of a particular 12ax7 variant without making it in the context of a particular circuit. My phono pre uses 12ax7's. I have tried (own) just about every NOS brand and variant of 12ax7, and as was the case after similar experimentation with various tube types in other pre's and amplifiers my conclusion was:

There are specific brand 5751's that can be magic in a particular circuit compared to all other 12ax7's or 7025's; and vise versa. In the case of my current phono pre, while some variants can sound very good (Raytheon 7025, Sylvania Gold 5751, and even the very rare CBS industrial 7729), when all is said and done, the best FOR ME and IN MY PRE are the Telefunken smooth plate 12ax7's; hands down.

In all my years of playing around with tubes I have heard nothing that definitively tells me that (for example) ALL 5751's sound better than all 12ax7's, or 7025's, etc, in a particular piece. IMO.
Frogman
Is it safe to say that a certain tube maintains characteristics regardless of component?(warm,detailed,etc)
I am trying to follow what you are stating...as I am looking for tubes for a preamp I just bought.
I can't answer for Frogman but I certainly think for the most part that a warm tube sounds warm where ever they are with a few exceptions. there is no doubt though, that certain tubes just don't work in all circuits. For me as a rule I tend to like 5751s in most situations. I did try 5751s in the output section of a Jolida CD player and it simply did not function. The sound was dreadful enough to make me think the tube had failed but it hadn't. The circuit for some reason was intolerant. Another exception was a highly modded ARC SP-6B which didn't change it's tone no matter what I put in it. It was brutally frustrating and a terrible combination with my speakers.
There are cases where the lower mu doesn't seem to work either. I have some real old unmodded vintage integrateds that used 12AX7s in the preamp section and frankly need the extra umph. A couple of them came loaded with Teles before tube rape was common. Curiuosly they respond quite well to current production in many instances where I have replaced the old tubes. The old tubes I then put into new amps and many sound fine go figure!
Mechans, you answered for me very nicely; actually.

***I certainly think for the most part that a warm tube sounds warm where ever they are with a few exceptions. there is no doubt though, that certain tubes just don't work in all circuits***

I completely agree, although I know some will disagree. I currently own one piece that uses 12ax7's, but own and use three that use 6dj8's. In all three pieces the Telefunken 6dj8 produces a full bodied, dimensional sound with a timbre closest to "neutral" as I define it; reminiscent of the classic Audio Research tonality. In one of the pieces, a modded Melos 222c occasionally used for it's line stage, the Teles' fullness and lack of zip or edge is too much of a good thing for this preamp which is inherently on the dark side. With this pre, West German Siemens 7308, which yields a brighter, less corpulent sound, with excellent high frequency extension is
much better. I hear similar tonality/timbre from my Tele 12ax7's in my
phono pre.
I should have said: "I hear similar tonality/timbre from my Tele 12ax7's in my phono pre as I do from the Tele 6dj8's in my linestage"
Man I cant wait to get some different tubes!!
I am still getting used to the sound of this Thor, but is is very good.
Does anyone have experience with Phillips Miniwatt 12at7 from Holland factory?
Another Thor owner suggested the Miniwatt/GE 5751 3 mica black plates combo.
Mc,
Buy all means get a pair. I really like them, i use them in my VT 5.5 pre-amp, i also like and use the Phillips Mini Watt 12ax7. Very smooth i like them, as usual YMMV......
treasure tubes kt88-z

got `em!!! i got them this morning. i fitted them and left them for 20 minutes or so then set the bias. left them another 20 or so minutes then checked the bias again and then to the good stuff! from the off these are an upgrade! very open sounding. i can already hear the top end is extended. my 1st and so far only track i`ve listened to is k.t. tunstall silent sea off the eye to the telescope cd. her closely mic`d voice sounds just incredible and incredibly real! the weight and texture to her voice is just right and mind boggling! she`s right there in front of me. soooo much detail in her voice and the sharp intake of breath you hear in between her lines! i couldn`t help listening to this over and over! the bass is deep, detailed, darker, warmer and textured. acoustic guitars have realistic tone, weight and that zing that acoustic guitars have. you can hear each string being plucked. the noise floor is extremely low on these and the back ground is silent. after installing these, the first thing i noticed was the lack of low level buzz coming from my speakers. if i put my ear up to the speakers i get a just about audible deep hum.

the soundstage is pin point accurate and the seperation of the musicians is very freaky. lots of air between the musicians! the soundstage is less deep but by no means flat. it`s much easier to get that sense that the drums are behind the singer. you also feel you can almost see the performers. you can also hear k.t. tunstals lips close and open as she`s singing and her voice actually sounds like it`s originating from her throat. by the way her voice on this track will leave you needing a cold shower!!!

the most amazing thing here is i have about another 298 hours to go before they`re broken in! and the sound is said to improve! wow! i`m off to do some more listening to my other favourite cd`s. my plan now is to fully break in these tubes then do one last tube roll between all the 12ax7`s and 5751`s before i make my final choice of tubes for this amp and system. so far i have to tell you i`m amazed at this sound coming from my speakers. more to come later today guys. this is just the initial "straight out of the box" review
another update.....

i had the telefunkens in this mix and and the sound was amazing, extremely clear, forward, immediate, weighty with a hint of warmth, pretty much like someones turned the main light on and you can see everything clearly and solidly.

well i had an idea. i don`t mean to tube roll this early on in the experiment but i read somewhere that the psvane 12ax7-t`s have a synergy with the kt88-z`s, so i swapped them out. in went the grant fidelity matched 12ax7`s. now it`s like someone switched off the main lights, lit several candles so you can still see all the detail but with more shading and more darkness in between, then lit a log fire! WOW! on a seduction level i`d score this mix as a 20 out of 10!!! you get all the detail but accompanied by the sexiest warmth ever! the forwardness has gone and replaced by naturalness with a sexy warmth. the bass is deep, detailed, punchy, slammy when needed, textured and all accompanied by a sexy warmth. voices are just plain sexy!!! the highs are sweet and clear and extended. the bottom end is extended too and accurate. it`s accurate all the way through the frequencies. there`s an amazing dark pleasing background that allows instruments to work their magic on you out of thin air. seperation in the soundstage is 1st class. all this with not quite 5 hours on the tubes! i`m in lurve already and i think i still have heaven to come! these tubes work extremely well together and so far it`s a matter of taste between the psvanes and telefunkens. but saying that, there`s a very long way to go and all tubes are going to get their chance to do their thing once the kt88`s are fully broken in but the psvane 12ax7-t`s will be staying in for the duration of the break in. this is a jaw dropping set of tubes gracing my amplifier so far!
Second the Phillips Miniwatt 12ax7 recommendation. Very good tube in my phono pre. A little brighter and more aggressive than my Teles, but not thin like some others, and with good body.
Grayf,

Are your 12AX7 Telefunkens ribbed or smooth plates? Also, if they are new old stock, I found that after around 30 hours or so my Telefunkens started to break in and added a nice sweetness to the sound.

I made the switch to tubes about three years ago. I am fortunate that I frequent a stereo shop here in town that has been around since 1947. I'm friends with the owners and they let me bring home all sorts of tubes to audition. It really is great how the sound of a system can be tailored, and you are doing what it takes to do that with your system. And please keep your updates coming. I enjoyed the process of dialing-in my system and it'll be interesting to see where you take your system.
hiya reynolds,

unfortunately the telefunkens are seconds so i guess they`re broken in plus i have about 50 hours on them. they are the smooth plates. i wish there was someone local to me to get tubes off or to swap. i`ll break in the kt88`s then do some proper evaluations of all the 12ax7`s and 5751`s. i`m really excited at that prospect! i only swapped the telefunkens yesterday because everything sounded a little too forward for my ears. i`m very sure the changes will be a plenty before the kt88`s are broken in.

things have changed quite dramatically since yesterday with the kt88`s aswell. everything sounds a lot more solid all round. the sound seems darker with very deep bass. voices also seem to have created more atmosphere too and are even clearer. there`s a ton of detail too. the soundstage is very large and very solid. the best imaging i`ve heard yet. if they stayed sounding the same as they are now i`ll be a happy man but i`m currently on just 28 hours so there`s still quite a journey with these to come. i`m loving the bass i`m hearing! i`m hoping i`ll have about 150+ hours on them by next sunday. it`s funny but i keep thinking the sound couldn`t possibly get any better and then it goes and gets better! amazing! the worst i`ve heard these kt88-z`s was last night. voices sounded a little shut in but that didn`t make them sound bad though. they sound very open today. some of the sounds i`ve heard are also hard to describe aswell. i told my friend the kt88`s turned up yesterday and he`s straining at the leesh to come around for a listen but i`ve told him to wait a couple of weeks. he had a cheap valve amplifier many many years ago and loved it. i think i`ve stirred his passion up again!
i just had a rare stroke of luck! it`s sunday evening here, and all my neighbours are out! i put on dave gilmours cd on an island and played it above my normal listening levels and as a real bonus, for the whole of the cd not even a car drove past let alone a bus! how amazing are these kt88-z`s!!! i`ve just been blown away by them! the bass is tremendous and so beautifully rounded. on one track ("take a breath") the bass growled. the atmosphere on each song is amazing! the tones dave gilmour gets out of his guitars are pure magic. my favourite tracks on this cd are the last 3 tracks "smile" "a pocket full of stones" and "where we start" are in a different league through these tubes. closely mic`d voices through this system are scarily real!!! on "a pocket full of stones", the start of the track is just gilmours voice accompanied by a piano, this sounds truly haunting now. incredible amounts of atmosphere and emotion and he sounds so isolated. his voice fills the soundstage and you can pin point the location of his voice. on the last track "where we start" his guitar has a smooth warm feel and he has that amazing ability on certain notes where needed to get that sheen that hits the spot with all of us and these kt88`s pull that off with such ease. there`s not only massive amounts of information on a disc that these tubes can extract but also massive amounts of information within the notes being played themselves. you seem to get it all, texture and tone!

on saturday i likened listening to these tubes to having the main lights off, candles on with a warm fire glowing, well i stand by that even more so now. it`s like watching a dark scene on a bluray disc through a stunning television being able to pick out all of the pleasing brighter detail while still being able to see all the various darker details and shades with the greatest of ease. these are remarkable tubes, and to think they`re only 35 hours old!!! how much better are these gonna get???!!!
need some advice. there`s a pair of SYLVANIA JHS 5751 BLACK PLATE TUBES triple mica square getters for sale fairly cheap. are these good tubes to fo for? they don`t have gold pins, just normal ones. thanks guys
Yes, those are good tubes I'd snap them up if I were you. That being said, you seem to prefer the 12AX7's to the 5751 in your setup (though that might change when your Treasures have completely broken in). If you get them and decide you still prefer the TF's, you'll be able to find someone to take them off your hands (I would).