Little Dot Tube Amps: Vacuum Tube Rolling Guide - Page 43

Hi Mojo35,

 

There is no such a thing as Sylvania gold grid tubes. What you are referring to are Sylvania tubes with gold plated pins. Some people are getting insane prices for these JAN (Joint Army and Navy) 5654 tubes.

As mentioned previously on this site, inexpensive Sylvania JAN 5654 tubes made in the 60' and 70's are identical to the ones with the gold plated pins, but without the gold plating on the pins, and they sound exactly the same. The way to identify these inexpensive tubes is to look for Contract Number DSA 900  on the box. Here is an example of the print line on the box: CONT. NO. DSA 900-67-C-9983 (This tube is from 1967).

 

Good luck tube rolling! I myself the have the 6N6P gold grid power tubes together with the Tung Sol 6AJ5 driver tubes, and in my system I am perfectly content to stay with this combination. I did notice that there is a slight variation in the sound between different years of the Tung Sol 6AJ5 tubes. The 1945 ones I tried first were very good, but a later 1960's pair had even stronger bass. The mid range is excellent, and the treble is absolutely gorgeous with crystal clear shimmering highs.

 

Would like to try the 6N6P-IR tubes, but I am waiting to find a bargain - I never paid more than $8 for a tube yet.
 

 

I currently have the 6H30PI, I'm looking for better bass with my Beyer T70's.

 

They sound great with my Auzentech Bravura sound card with AD797 opamps but it needs a little warmth. With the LittleDot the mid bass is lacking and sub bass is almost non-extant.

 

Which is strange to me because my HD650's have a pretty good kick with metal and electronic music.

 

I've got to admit the Sylvania JAN 5654's sound just as good as the "gold pins". I haven't used the JAN's for a while because I was spooked by a blue glow from both tubes. I have since learned that the "blue glow" isn't a bad thing. Your post prompted me to give them a listen again and I'm immensely enjoying them now.  

mab1376, The HD650 is very good with kick bass and bass generally, although I found it on my LD more blurred compared to the HE-500s. I am not familiar with the T70 but after a glance through Head-fi it seems that it is not the most bassy type of headphone.
 

britt2001b, The Sylvania JAN 5654W tubes were a few months ago my favourites =) and they are nice - a somewhat warmer and darker version of the very nice GE JAN 5654W. But after all the fun..., I am content now with my LD tubes ;).

Edited by Acapella11 - 1/17/13 at 5:23pm

After spending a few days with the HE-400, I took the chance to roll some tubes from my stock with new impressions.

 

First, I hate to admit it but tube rolling makes much less of a difference on the HE-400 than it did on the HD650 (driver tubes, didn't touch power tubes). The sound balance changes somewhat but soundstage and resolution just don't seem to be affected that much (even trying the HE-400 on my iBasso D10, portable SS amp, I'm not sure I could tell the difference in an ABX test, although the IV SE is better and more detailed). This being said, there are differences.

 

I tried my good old (stock for me) CV4010 again. Hadn't used those in a while as they had started to feel too warm and un-neutral, with an over-emphasized bass (and not sub-bass) hump. On the HE-400, they give a pleasant and open presentation with good instrument separation, are just a bit warm, and the extra bass and rolled-off highs make the headphones seem less spiky. Still, it lacks PRAT and feels unnaturally warm on the HE-400. And there was still not enough bass.

 

So, I tried the 6AJ5 again (had tried them right after getting the headphones and was originally disappointed). This time, I felt the 6AJ5 complemented the HE-400 quite well with a great airy soundstage and shimmering highs (but not sibilant). Still a lack of bass and no sub-bass, and the whole presentation could have been more dynamic, but it feels like a safe and pleasant everyday choice; not a very challenging sound in any case.

 

I am starting to think that none of the tubes in the 6AK5 family can really be quite dynamic and "fun" enough to get the HE-400 moving (and the HD650 also in a way, which are a bit on the dark and slow side in the first place). Not that the 6AK5 tubes are inferior, they are in fact very well suited for headphone amps, but they are always a bit rolled-off in the extreme frequencies, which makes them an easy listen. The 6AJ5 come close to being dynamic but aren't exactly "fun" and challenging like the CV4015 or even some spiky treble EF91 tubes can be...

 

Speaking of the CV4015, whereas their detailed upper-mids and treble complemented the HD650 very well (made it a tad too bright in fact) while maintaining a tight bass with no hump and just a touch of sub-bass (difficult to get on a tube amp like MKIII/IV), those same characteristics make them difficult to listen to with the HE-400, at least for some types of music. Guitars sound the best I've ever heard, so do all the crashing treble-y brass instruments, but the balance between bass and treble just seems out of whack. Maybe the lack of bass and sub-bass I'm hearing is just brain burn-in, but still it's a bit annoying as these are by far my most engaging tubes.
 

Edited by Audiofanboy - 1/18/13 at 1:48am

 

Like I said though, they have a great sub bass kick with my soundcard, just lacks a little warmth for my taste.

Thank you for all your input i now have these on the way.
5 NOS Sylvania Miliary grade 5654 - 6AK5W - EF95 black plate
http://cgi.ebay.ca/ws/eBayISAPI.dll?ViewItem&item=221178531683#ht_500wt_922

Looks like, the tubes will be in my possession before the amp. I look forward to contributing more to this thread than questions.

However another question does anybody use the beyerdynamic DT 1350's with there amp? And if so what tubes are you using?

Gary

 

Hi Audiofanboy,

I have exactly the same impression , which is why I keep the CV4015 tubes.

 

 

This effect also happens with the HE-500, although the treble seems to be not as refined with the HE-400. A darker phone / or a decent level of "relaxation" of the headphones is important to make 6N30P + CV4015 work non-fatiguing. I have read that the HE-400 sounds a bit more treble spiky and there are also frequency response curves, which show different quantities and qualities of treble spikes between HE-400 and HE-500. Check this out for details:

http://www.head-fi.org/t/551345/hifiman-he-500-he-as-in-high-end-please-post-your-impressions-loan-pair-for-uk-pg-28/2445#post_9024251

 

I could listen a bit to 6N30P-EV + CV4015 but it becomes fatiguing. 6N6P-IR tubes fix that for me whilst keeping dynamics that are reduced with 6N6P tubes.

 

Consider that I am saying this with regard to my current headphones. I think 6N6P tubes perform better when your headphones fit from the design already the performance of the LD MK III / IV, which means they have 120 ohm + and go well with 300 mW (e.g. Sennheiser HD650, 103 dB sensitivity, 300 ohm impedance) or very good sensitivity with at least a bit of impedance (e.g. Denon AD-H5000, 106 dB, 25 ohm) in order to not generate a noise floor.

Now, Hifiman HE-500 are magnetostatic  headphones (89 dB, 38 ohm) and sensitivity is low as well as impedance. This makes these headphones not very useful for headphone amps as the Little Dot III / IV. Theoretically, they just need more power to work fine. However ;), I think here is where the higher gain tubes can shine: Gain for driver tubes: EF 91 > EF92 > EF95, for power tubes: 6N30P > 6N6P-IR, 6N6P-I > 6N6P. The sound quality of CV4015 tubes from the EF 92 family seems to find no match in the EF91 family (Audiofanboy will update us on this one I guess ;) ) and 6N30P sound stunningly detailed with a very precise bass, not very deep though. 6N30P tubes tend to sound a bit bright and hard, this is the main disadvantage I found. The 6N6P-I tubes sound warmer and the 6N6P-IR sound for me like a higher quality version of the 6N6P-I, as in more spacious, deeper bass whilst keeping treble extension. So after all, it comes for me down to a pairing of an EF92-tube (CV4015) with a 6N6P-I type power tube (6N6P-IR).

 

I am explaining this to put you into the picture that I am basically running a headphone on the LD MKIII, which is not considered suitable but still I think the sound is good. Only and importantly, the gain of tubes plays a more important role for the sound quality. 

 

Audiofanboy, interesting observations overall, I can exactly see where you are and I guess you are already trying to fit the power tubes to the CV4015 . It might not work with every phone but I found this path giving the best sound.

 

EDIT: Updated thoughts on the gain of tubes with regard to sound quality on the Hifiman HE-500.

Edited by Acapella11 - 1/19/13 at 6:37am

Audiofanboy and Acapella11, I'm exactly in the same situation. So I'm having high hopes for the 6N6P-IR. Maybe the perfect setup, if it adds a kick and body to the subs. Right now, I'm waiting for an answer about matching and if it's +, I'll buy them straight away. I listen my LD MKIV with HD 580 and HD 25 1-II. And lately as a preamp with these: http://www.fl-electronic.de/neuklang/images/x-Space.jpg, Mission X-space, they work very well together, balanced like I never heard before from my flat panels, it was surprising. Surprisingly awesome, fat and round dynamic bass which doesn't distort, which is notable especially because the X-space isn't exactly a bass champ but an air surfer. And with LD now it stays dynamic at low volumes too. This is why we love tubes after all.

Edited by hallom - 1/18/13 at 5:11pm

I've been researching tube amps for a couple weeks and am minutes away from pulling the trigger on a Little Dot MK IV.

 

I thought I'd better research the tubes real quick to determine availability and replacement cost. A quick Google search and BAM! here's this thread.

 

Amazing job OP. Amazing to find stuff like this. I could be just starting out on a new interest or hobby and find stuff like this.

As promised, and after getting a metric ton of tubes in the mail, here are my thoughts on different EF91 tubes.

 

 

Mullard CV4014 KB/D 6064 made in Mitcham, O-getter and open structure below getter, blue side glass and inside visible (no cage like element between anodes). Both tubes are identical in construction and flash when turned on (they dim shortly afterwards), one only has military markings and was made in 1972, the other also has the old Mullard logo and M8083 and was made in 1968. They sound exactly the same. They have a very large soundstage, a very airy treble forward presentation with great instrument separation. Highs can be a bit spiky and borderline sibilant but are always extremely natural and spot on for vocals. Bass has weight and quantity despite being quite loose (but if it's in the song, you'll definitely hear it loud). Mids are fine but not exceptional. This tube feels like a looser bass-ed CV4015 with more space and treble, useful for specific types of music. They really wake up the HD650, but are a bit spiky on the HE-400 (and bassy). My impressions match what's on the first page.

 

 

Another Mullard CV4014 KB/D 6064, made in Mitcham in 1958, identical tubes with same date code, blue glass, a cage like element between the anodes, D getters with a cage underneath; they don't flash when turned on. These sound quite neutral, balanced across the frequency range, and quite tame for EF91 tubes. Highs are not spiky or sibilant, detailed but not spectacular like other EF91 tubes; at least the highs aren't fatiguing or painful. Instrument separation and resolution are very good (maybe not quite as good as the later CV4014 reviewed above, but it's hard to tell without ABing immediately). Mids and mid-bass are pretty good and don't detract from the rest. Bass isn't too loose and just rumbly enough to be entertaining. Overall, this is a very versatile tube that sounds like a tame crossover between an EF92 and EF91 (which is weird since the CV4014 from '56 I tried and reviewed two weeks ago weren't like that at all and had the treble-centric triangle presentation I hate, maybe factory improvements or better burn-in? Those were the first production years for CV4014, so different batches with different sounds are to be expected). Another pair of tubes I could live with if I had to!

 

 

Brimar CV4014 (only markings on the tube with "Made in England B.V.A." and indecipherable factory codes), silver glass all around the anodes that hides the internals, identical O-getter tubes, I'd assume from the getter that these are 60's production or later. These are different from anything else I've heard before. The bass is quite extreme and other-worldly. Sure it reflects what's in the music, but it renders the bass in such an interesting and fun way that you just want to keep on listening. Although the bass may or may not be perfectly hi-fi like (debatable), it is still very well controlled and powerful (drives the schiit out of the HE-400 and makes listening to the HD650 an absolute riot!). The treble is very detailed and airy; still a bit spiky on the HifiMAN but perfect on the Senns, pleasant overall (doesn't make my ears bleed), not quite as refined as the CV4014 though. Mids could be a bit more emphasized but don't detract from the global presentation; this gives these tubes a fun U-shaped sound signature. The soundstage seems boundless which pairs very well with the extreme bass that flies in all directions (think fun fat controlled bass like the CV4010/M8100 but in a grown-up version, not perfect but fun). One of the easiest tubes to listen to in the EF91 family in my opinion (and many EF91 tubes are hard to listen to for over 30 minutes...), great listen on the HD650, awesome bass kick. This is one pair I'm sure to burn in a bit.

 

 

Mullard CV138 KB/D, made in Mitcham in 1952, blue glass, D getter with an open top part (flying copper leads and black rectangle below the getter), no cage between anodes, internals look like the basic Mullard EF91 of the same time period. They sound the same too, that is SS-like and a bit sterile. Detailed and over-emphasized highs that quickly get grating. Recessed mids and thin loose bass. They might improve from a long hard burn in like many basic Mullard EF91s do but knowing the results in advance, I don't feel like it; the sound signature wouldn't change that much anyway.

 

 

Mullard CV138 6AM6 KB/D, made in Mitcham (no factory code but KB/D) in 1954, blue glass, cage element between anodes, D getter on top of an open part. These are like the (noisy) CV138 I reviewed 2 weeks ago, but they seem to have had an easier life (they may be NOS or close to new). They have an extremely wide soundstage. The bass is loose, slightly punchy, pleasant and unobtrusive. The presentation is basically treble-centric, but not sibilant; mids are a bit recessed. Overall, these tubes are fairly detailed, but not quite as much as the best EF91 tubes. Again, I could probably live with these if necessary, and a bit of burn-in might help.

 

That's it for now, there's a few more pairs I've tested, I'll post impressions tomorrow. I have to admit these EF91 really have quite a lot of treble. After a whole day of listening to different tubes, my ears feel like they're just about ready to give out, and my head kind of hurts... This is when I miss the 6AK5 love a little.

Edited by Audiofanboy - 1/30/13 at 6:15am

Thanks for all your great info! I'm totally new this...just ordered my first set of cans (Grado 225i) and I'm thinking of buying the Little Dot 1+. I don't know anything about tube rolling yet-as this will be my first exprience w/ a HP amp. Just curious-LD offers:

 

• Replace standard tubes with EF92 - additional $20 USD
• Replace standard tubes with WE408A - additional $50 USD

 

Would you advise me to stick w/ the tubes it comes with,or are these upgrades worth it IYO.

 

Much Thanks,

 

Mark

Thanks for all your great info! I'm totally new this...just ordered my first set of cans (Grado 225i) and I'm thinking of buying the Little Dot 1+. I don't know anything about tube rolling yet-as this will be my first exprience w/ a HP amp. Just curious-LD offers:

 

• Replace standard tubes with EF92 - additional $20 USD
• Replace standard tubes with WE408A - additional $50 USD

 

Would you advise me to stick w/ the tubes it comes with,or are these upgrades worth it IYO.

 

Much Thanks,

 

Mark

Great job reviewing the EF91 tubes Audiofanboy , surely no one expected a bass heavy tube there! Seems like you discovered two nice tubes there. Also nice that you could test with HD650 and HE-400 headphones that adds value. I would to be careful to buy the ones, which are not nicely compatible with HE-400. Cool!

 

Markm1, I am not familiar with the LD MKI+, but generally it was found that it is cheaper to buy tubes from ebay or a cheap online shop than from David ZheZhe himself.

Edited by Acapella11 - 1/19/13 at 6:23pm

Hi all.  I am in need of help.  I just purchased and received a Little Dot Mkii amp.  Delivery was blisteringly fast (2.5 days to Montreal).  However to of the two tubes were broken, one of each.  LD will send replacement tubes, shipping is  "15 to 45 days".

 

I don't have a lot of time for reading threads right now so I was hoping someone could point me to a a fairly cheap set of tubes so that I can try out the amp and see if it works and get a feel for it.  Phones are Grado SR80 and this is my first foray into headphones and amps so I would sure like to hear this thing.  Later when I have more time I will read up on tube rolling .

 

 

Thanks!

Edited by django1 - 1/19/13 at 10:01pm