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Little Dot Tube Amps: Vacuum Tube Rolling Guide - Page 40

post #586 of 10909

Thank you Audiofanboy, the 6n30p-dr supertube is out of budget, but I'm hunting a pair of CV4015 now.

I use a rocket logo 6J1P-EV gold platinum (with 6N6P OTK gold grid sounds much more balanced in the highs and more power in the lows, then with the supposedly better 6H30Pi-EB, which maybe shines with a different driver), which sounded very precise at the beginning, but now I have the feeling their bass loosened up a bit around 40-50 hours, or maybe I'm just imagining it, but defto I want to try the CV4015.

Edited by hallom - 1/3/13 at 6:42am
post #587 of 10909
Originally Posted by hallom View Post

Hey Guys, according to your experience, which one is the most neutral - least warm sounding tube setup (power+drive) around?

For me, the 6H30-EV appear more like the 6H30-DR as described by Audiofanboy. They are my brightest power tube and at the same time very detailed. They can be just the right tube when paired with a not too bright driver tube. The only disadvantage I found was a lesser deep staging. Although the overall performance is impressive, spatial depth is limited, the tubes sound forward.

If you are in for a straight but rather "hard" and a bit treble biased presentation to match your setup, surely look at 6H30-EV plus CV4015. 


I totally agree with Audiofanboy with respect to the CV4015 and the 6AJ5. CV4015 is my personal favourite: very balanced, very detailed, very good resolution and dynamics. Since both (my 6H30-EV and the CV4015) tend into the bright direction, on my setup, they become fatiguing after a while. In order to avoid this, I have paired the CV4015 (1980, no Mullard logo) with 6N6P-IR (1974), which deliver a wide and deep stage and great dynamics (extended bass and treble). The combination is not very warm, rather natural and neutral, I'd say and my favourite. 

post #588 of 10909

Acapella11, is the 6H30-EV the same as the 6H30Pi-EB?

BTW do you guys know anything about this tube? http://www.ebay.com/itm/2x-TESTED-MATCHED-6N6P-OTK-5-Military-GRADE-GOLD-GRID-TUBES-ECC99-E182CC-/251200575992?pt=Vintage_Electronics_R2&hash=item3a7cb899f8

post #589 of 10909
Originally Posted by hallom View Post

Acapella11, is the 6H30-EV the same as the 6H30Pi-EB?

BTW do you guys know anything about this tube? http://www.ebay.com/itm/2x-TESTED-MATCHED-6N6P-OTK-5-Military-GRADE-GOLD-GRID-TUBES-ECC99-E182CC-/251200575992?pt=Vintage_Electronics_R2&hash=item3a7cb899f8

6H30-EV is Sovtek, 6H30Pi-EB is Electro-Harmonix.


EH are more expensive than Sovtek, both tubes have different qualities but the EH might be more detailed and warmer. The EH are stock on the MK IV SE.

post #590 of 10909

this is also advertised as PI-EB and Sovtek, I have the same one, so which one is 6H30-EV?

post #591 of 10909

Same tube, different transcription. Sovtek can be advertised both as 6h30p-ev or 6h30pi-eb. Whereas I've never seen the Electro Harmonix advertised as 6h30p-ev. The EB/EV writing means long life (>5000 hours).


It's the same translation problem with 6h6p/6n6p, or 6h30p-dr/6n30p-dr.

post #592 of 10909

Hi Hallom, as described by Audiofanboy my 6H30 tube is a Sovtek 6H30П-EB and transliterated properly to 6N30P-EV where P is equivalent to Pi.


Your link (below) leads to a tube of that kind:



PS: If you have the budget and like a deeper stage, keep the 6N6P-IR on the short list :)

post #593 of 10909
Thank you Guys, I can't wait to try C4015, then the next step will be the power tube.
post #594 of 10909

Finally got my latest ebay tube purchase yesterday. 10 used EF91 type tubes for 9 euros, not too shabby I think; it'll keep me entertained for longer than 2 beers at the pub or a movie theater ticket for the same price!


Anyway time for my EF91 shootout. Out of the 10 tubes, 6 turned out to be "pairable", 4 being virtually identical. There were no actual EF91 tubes in the pile, but only CV138 and CV4014 versions, so all UK military (which is why I bid on this in the first place).


First pair I tried were some blue glass CV138 KB/D (crowbar, 6AM6, no logo). Deciphering the old military markings, these should have been made by mullard in 1953 in the Mitcham factory. Both tubes were identical and a had a slightly elevated noisefloor that didn't really impair listening. They're like these ones (the ones of the picture with "6AM6" also written).




These tubes were actually quite surprising in clarity and transparency, with shimmering natural highs and very a large soundstage with great separation (more wide than deep though, unlike the CV4015/M8161 which I find more holographic and "3D-like"). Bass is a bit loose like all EF91 tubes, but goes quite deep and is great for non-fast music (absolutely great for jazz, less with electronic music). Mids are fine but uninspiring unlike the best EF95 tubes. Overall, one of the most neutral tubes I've tried, but not quite as musical and detailed as the CV4015; the treble-centric presentation can get tiring very quickly though, and the CV138 can sound quite SS-like, which many might not like. I would only use these occasionally for specific genres of music.


Second, I tried two blue glass CV4014 KB/D (crowbar, 6064, no logo) tubes (special quality EF91, more ruggedized on paper than CV138, which it more or less replaces). Military codes supposedly show they were made by Mullard in 1956 in Mitcham factory (which is weird since the literature says these special quality types CV4xxx were made from the late 50s onwards). They are almost identical to the CV138 above in construction but an additional "cage" element below the getter than effectively hides the top of the filament that was visible on the CV138 -so no glow really. They look somewhat like these.




Logically these tubes should be better than the CV138 from the same decade, and they are quite nice and very similar, shimmering detailed treble, loose jazzy bass... But somehow, I just couldn't enjoy these the same way I did the CV138. There is an ever-so-slight difference that is difficult to pinpoint that makes the sound of these tubes less inspiring and musical (funny thing is they seem to be cheaper to buy too), maybe colder or more neutral than the CV138. Overall, very good jazz and acoustic tube. I suspect that there are better CV4014 tubes out there, maybe from later decades with a different construction (if anyone is looking to sell a pair of 70s CV4014/M8083 with blue glass, do contact me).


Last tubes I paired and tried were some grey CV138 KB/EN (crowbar, no logo). Decrypting  the codes, these are basically old-world ruggedized EF91 tubes made in 1951 by Thorn-AEI in the Sunderland factory for the UK military.




One of the tubes was clearly weaker than the other one, so I'll never really use these for serious listening, but these have a very interesting sound, unlike other EF91 tubes I've tried. Bass is full and pleasant, even though it doesn't go down very low. Highs are still very detailed and natural, but not sparkly or sibilant like many EF91 tubes. Soundstage is quite large and instruments are well separated. Overall, these tubes are like a laid-back version of the mullard EF91 tubes, just less treble and fatter bass (but not bloated), possibly less detailed and not quite as good at staging as the two pairs reviewed above. Very pleasant for calm jazz listening. I'd love to find a cheap pair of these tubes NOS!


Anyway, if you're looking for absolutely neutral or "cold" tubes, the military EF91 variants seem to be a very good choice if you can live with more treble and looser bass.

post #595 of 10909

A few additions to my earlier post after a couple extra hours of testing.


The CV4014 I reviewed above are indeed clearly inferior to the early 1950s CV138, less bass and more metallic treble, not unpleasant, but I have much better tubes to listen to. Interestingly, it's makes me realize how good the CV4015 are. They may seem a bit treble forward, but they are probably the most balanced tubes I have actually. On the other hand, the EF91 family is clearly treble-oriented.


I think I found out what makes the difference between my CV138 and CV4014. Although the military codes KB/D on both types show a "pumping process" at the Mullard Mitcham factory, the factory codes on the CV4014 show an R for Mitcham, whereas the CV138 have an obscure J that, upon further investigation, could be a Tungsram factory in Tottenham bought by Philips (Mullard) in 1952. Different factories would explain a noticeably different sound.


One of the "un-pairable" tubes in the batch was also a CV138, virtually identical to the ones reviewed in construction (only difference I could spot was a few soldered wires at  the base that seem more copper-colored, absolutely identical otherwise), labeled with B.T.R.W and CV138 in a circle, no military markings, no factory codes. My best friend google tells me BTRW is simply British Tungsram Radio Works, basically Tungsram UK at the time. Tube was made no later than 1952, since the factory was Mullard labeled afterwards.


Since it seemed reasonable, I paired that tube with one of the other CV138. Well, guess what, it sounds great, the same as the CV138 above, and possibly with better bass extension and clarity (even though it's difficult to tell with one tube) but very similar. So, yes, it could just be that these obscure Tungsram factory early 50s military tubes are worth investigating.


Has anyone else tested 50s era CV138 tubes?

post #596 of 10909

Thank you Audiofanboy for sharing these detailed impressions smile.gif.


The EF91 tubes haven't been looked at much, so it is really great you tried them! It sounds like there are some hidden gems from a formerly not mentioned Tungsram factory.

How long did you burn them in? May I ask you to update this after each tube has been burned in like 40 hours (if you can be bothered) with a ranking and short summary per tube?


I personally found my CV4014 (KQDD/K, 83-31) although very nice in terms of treble extension and quality too "head-biased" as in that the whole signature shows a bias like a triangle standing on the tip with the treble most emphasized and the bass least.


From what you wrote, it also sounds like it might be interesting to have a closer look at different CV4015 tubes (years, labels) as this still comes out as your (and my) most favoured tube. Just a thought. If anyone else uses a CV4015, he/she might like to post details and impressions.


Nice work.

post #597 of 10909

This is slightly off topic, but I thought it might still be interesting.


For many this an old story but I haven't been paying much attention to cables due to them being one of the least sound influencing parts in the setup.


Well, then I connected DAC and LD with a new phono cable. Both were different kinds of oxygen free copper budget Hifi cables in the range of $30. Now, the difference is quite well noticeable. With one (Atlas Elements, old plug) the sound is lusher, warmer and voices have more body. On the other hand with the second one (QED Profile), the sound gains dynamics, sparkle and definition.


Actually, in my ears the difference is great enough to say that the overall sound is a bit too boring for me with one (Atlas) compared to the other (QED). System matching is the key, as usual.

With respect to tube rolling, of course relative difference can always be concluded but for some statements it is good to keep the complexity of the setup in mind (YMMV ;) ).

Edited by Acapella11 - 1/6/13 at 9:05am
post #598 of 10909

Yes, I'm sure there's also much left to test with the CV4015. I think the later early 80s tubes with the small logo might be different or slightly inferior to the late 70s early 80s large logo, from what I've read; so I wouldn't worry too much about those versions. On the other hand, I've seen on ebay (and received by mail in an other used batch a few months ago, but one was shattered and the other one dead, got my money back) older CV4015 with no logo, different glass, inner construction and getter shapes; so I know there are many versions left to try. No idea how they sound though.


About burning in those EF91 tubes. Well, it's sort of a moot point really since all those tubes were used (quite used in fact, many are more like dying), so no burn-in is required (couldn't tell the effects anyway). Let's say it was more of a " test and toss" sort of review for those old tubes. Now, I need to find them NOS for a few bucks, which might be challenging.


Out of curiosity, do your '83 CV4014 have a mullard logo or just military codes? Blue side glass? I definitely agree with the triangle presentation, I found my '56 CV4014 to be this way too. Very clear, airy and large treble on the top of the head, and loose anemic bass below that it just sort of there and not dynamic, giving the impression of a biased soundstage. Which is why I just don't see myself using these anytime for serious listening. Again, the CV138 were better in that aspect with decent bass and a more balanced soundstage impression.


Incidentally, in that same batch of broken tubes I just mentioned above, I also had two CV4014 from the early 70s (only one worked though, other one had lost vacuum). I re-tested the one that worked (no logo, arrow, 6064 7301 CV4014 KB/D => Made in Mitcham in 73 by Mullard, halo getter unlike the older tubes I reviewed) with another good tube (the Tungsram CV138). Again, it's difficult to know what you're hearing with one tube, but it definitely sounded better than my '56 CV4014, more musical and dynamic and better bass (deeper and tighter, still loose though). Sounded quite like the old CV138 in fact. If I were to pay more than a few bucks for a pair of these tubes, this is probably the time period I would aim for, just like my '76 CV4015.


Has anyone tried the CV5377 I keep seeing on ebay? They're supposed to be an even "specialer" quality EF91 than the CV4014, but I keep seeing the 1985 version around, which is kind of late. Ultimate EF91 tubes or last tubes out of Mullard factory with low quality control...?


About cables, 6 months ago, I took the decision to replace all my interconnects with DIY cables (Mogami cables and Rean RCA jacks, I had recabled my HD650 with the same brand and a neutrik jack a year ago already). I wasn't expecting much going from cheap hifi cables to quality copper DIY cables, but I was quite impressed with the results! Better transparency and dynamics, better separation; not a night and day difference (unlike the headphone cable) but a solid improvement all around. Cables matter. At least once you've reached a critical point in your set-up where every small difference can be heard.

Edited by Audiofanboy - 1/6/13 at 4:53am
post #599 of 10909

Hi Audiofanboy, these are my CV4015 and CV4014 tubes:


CV4015: no Mullard label, halo getter, 000-4015, CV4015, KQDD/K, 80-49, picture: http://www.head-fi.org/t/563884/lightbox/post/8892857/id/725931

CV4014: no Mullard label, halo getter, 000-4014, CV4014, KQDD/K, 83-31


I also heard good things about Mogami cables. Did you solder the cables yourself?

Thanks for the detailed response.

post #600 of 10909

Yup, soldered 'em myself; was my first DIY soldering job. Pretty difficult with a cheap cheap Chinese awful soldering iron, but actually pretty easy once you get the hang of it (despite the Chinese iron).


I do recommend the Rean RCA plugs (Neutrik NYS373 actually, Rean being like the cheap Neutrik essentially), convenient, cheap and easy to solder.

Here's the best link I found that has, like, everything you need to know to solder some cables.




Last piece of advice: kids, don't buy 5$/€ irons, you'll waste more on burnt materials and parts than you saved cheaping out on the soldering iron itself... And you'll eventually get another iron anyway.


Thanks, for the details on your CV4014 and 4015 tubes. it's that kind of detailed information that I always find myself needing when I'm looking at ebay ads...

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