Little Dot Tube Amps: Vacuum Tube Rolling Guide

[Dept_of_Alchemy]

Little Dot Tube Amps: Vacuum Tube Rolling Guide​

 
[size=16.0pt]A quick introduction: Who is this guide for? (plus some background)[/size]
 
When I purchased my first Little Dot amplifier in 2005 I was in a position many of you are in now.  I was new to high end headphones, and curious about the ‘tube’ sound. Being a student at the time I wasn’t in the financial league to afford a high end tube amp, and I began to look for the best “bang for the buck” I could find in an intro level amp.  It was in that context that I purchased my first Little Dot amp and began my very satisfying journey through the world of tube rolling.  Setting aside a little time each week, the following guide and tube ratings are compiled from notes I made during listening sessions with a Little Dot MkIII fed by a HeadRoom Max DAC (lossless files from MacBook Pro via USB).  My reference headphone is the Sennheiser HD650 and all of the tubes I listened to are matched pairs unless otherwise noted.  The tube descriptions and ratings in this guide are observations from my own subjective experience and as we often say on this forum - your mileage may vary.  I hope you will find this guide a useful reference and have as much fun reading as I did while writing it. Please share your own tube rolling impressions in this thread.  Happy listening!
 
 
[size=16.0pt]Which Little Dot amp is this guide for?[/size]
 
The tubes reviewed in this guide can be used in all current production (2011) LD tube amps.  If you are not sure which tube family works with your amp (including out of production LD amps), please refer to this list for more information or ask us in this thread.
 
     - DoA
 
 
[size=24.0pt]-= Contents =-[/size]
[size=10.5pt][click on chapter titles to go there directly][/size]
[size=10.5pt][sections marked in red are incomplete][/size]
 
1. EF91 FAMILY
1.1 Overview
1.2 Brimar EF91
1.3 Mullard EF91/6AM6
1.4 Mullard M8083/CV4014
1.5 Telefunken 6AM6
 
2. EF92 Family
2.1 Overview
2.2 Ediswan EF92
2.3 Mullard CV131/6CQ6
2.4 Mullard M8161/CV4015
2.5 MWT W77
2.6 United Electron EF92
 
3. EF95 Family
3.1 Overview
3.2 Amperex 5654
3.3 Chinese 6J1
3.4 Collins 6AK5
3.5 GE 5654
3.6 GE 5Star 5654 (Gray plate)
3.7 GE JAN5654W
3.8 Mullard M8100 / CV4010
3.9 RCA 5654
3.10 Voshkod 6ZH1P-EV
3.11 Sylvania 5654
3.12 Sylvania Gold Brand 5654
3.13 Tung-Sol 6AK5
3.14 Western Electric 403B
3.15 Westinghouse 5654
 
4. Power Tubes
4.1 Overview
4.2 Chinese 6N6
4.3 Russian 6H6P
4.4 Russian 6H6P-I
4.5 Sovtek 6H30EB
4.6 Electro-Harmonix 6H30Pi Gold
4.7 6H30P-DR
 
5. Conclusion
5.1 Can’t Decide Which Tube to Try?
5.2 Online Tube Sellers
5.3 Useful Links
 
.

 

[Dept_of_Alchemy]

 

[size=18.0pt]1.[/size][size=18.0pt]EF91 FAMILY[/size]

 
1.1 Overview
 
Known for its linear and extended presentation in the top-end but sometimes suffering from ‘boombox’ bass, the EF91 family of signal tubes is a great choice for jazz aficionados looking for that crystal-clear treble and who prefer (or do not mind) looser-than-neutral bass. The EF91 draws significantly more current (300mA) compared to the EF92 (200mA) and EF95 (175mA) families and therefore tends to run hotter as a result. When considering rolling these tubes be aware that some users have reported distortion problems when using tubes from the EF91 family although I have never experienced that problem with both high and low impedance headphones in my LD MkIII setup using matched Russian 6H6P-I power tubes (I suspect EF91 distortion problems are caused by low quality or mismatched power tubes). Dip switches must be set in their correct positions in Mk-series amps before using this family of tubes.
 
Also Known As: EF91, 6AM6, CV138, M8083, CV4014, Z77, 8D3, HP6, 6F12
 
1.2 Brimar EF91
 
The first thing you’ll notice about this tube is its very unique bass signature. People who enjoy this sound would say that its bass sound is entertaining while perfectly reasonable people can also argue that it needs more control and texture. To be sure, this tube doesn’t produce a proper ‘audiophile’ bass but it is nevertheless exciting sounding and there isn’t another tube that produces bass quite like this. The Brimar needs a lot of burn-in and the bass tightens up noticeably after 20 hours. The mids are uninspired compared with some other tubes in this family but still an improvement over stock 6J1’s. This is a great jazz tube on account of its excellent treble response and listening to instrumentals with this tube is very enjoyable indeed.
                Bass: 14
                Mid: 10
                Treble: 19
                Detail: 18
                Soundstage: 17
                Total: 78/100
 
1.3 Mullard EF91/6AM6
 
Typical of the EF91 family, this tube needs a lot of burn in and its sound matures over time. The decay in treble energy with cymbals is excellent as well as treble extension. Bass and midrange are unobtrusive but not brilliant. Not to be confused with the great sounding mil-spec Mullard M8083.
                Bass: 15
                Mid: 13
                Treble: 18
                Detail: 14
                Soundstage: 16
                Total: 76/100
 
1.4 Mullard M8083/CV4014
 
It is immediately obvious from the first listen that this tube is clearly the class leader of this family. First visual impression of this mil-spec tube reveals that it is extremely well-built with solid top getter and a blue colored screen side getter. My matched pair has the large Mullard shield logo printed on the tube and is dual printed M8083 and CV4014. Compared to the other tubes in the EF91 family, this tube does not need much burn-in time, vocals are especially vivid and noticeably stand out from the instruments. The decay of treble energy is surprisingly realistic, and this tubes’ uncanny ability to express nuances in the treble frequencies makes listening to live jazz recordings with this tube a joy in itself. Overall the sound of this tube is very impressive, with the small caveat that it has a slightly loose bass typical of EF91 tubes.
                Bass: 18
                Mid: 17
                Treble: 20
                Detail: 18
                Soundstage: 18
                Total: 86/100
 
1.5 Telefunken 6AM6
 
This tube shows up relatively rarely on the market and it took some persistence on my part to find two tubes, but since it bears the celebrated Telefunken badge I decided to include this tube in this guide for the sake of completeness. Disappointingly, this tube failed to meet my expectations and even though it performed admirably well in reproducing treble frequencies, the sound in other areas is noticeably worse than the Mullard M8083 reviewed above. This tube also suffers from a particularly severe case of ‘boombox’ bass which is very distracting to me. I have to mention also that mine is not a matched pair which probably influenced its soundstage score somewhat.
                Bass: 13
                Mid: 16
                Treble: 20
                Detail: 16
                Soundstage: 15
                Total: 80/100

 

[Dept_of_Alchemy]

 

[size=18.0pt]2. [/size][size=18.0pt]EF92 Family[/size]

 
 
2.1 Overview
 
The EF92 family tends towards a more neutral sound with an emphasis on great vocal presentation, but the sound quality can vary wildly between different manufacturers. This is the only family of driver tubes that can be used on the older (out of production) LDII+ and LDII++ models (see List of LD Amps).
 
Also known as: EF92, 6CQ6, CV131, M8161, 6065, W77, V884, VP6, 6F21, 9D6
 
2.2 Ediswan EF92
 
One of my least favorite EF92 tubes, this tube has a harsh ‘digital’ sound that makes it fatiguing to listen to and the perception of ‘haze’ impinges on vocal music making the sound a bit too edgy and lifeless. Bit of a personal story, I actually first acquired these as stock tubes with the now discontinued LDII+ (my first LD amp) and it helped spark my enthusiasm for tube rolling ever since I discovered just how much better my amp can sound by rolling in different tubes. I don’t know if Little Dot still ships amps with this tube but if you are currently listening to only this tube I would highly recommend for you to check out some of the other tubes reviewed in this guide, you will be pleasantly surprised.
                Bass: 13
                Mid: 13
                Treble: 9
                Detail: 10
                Soundstage: 14
                Total: 59/100
 
2.3 Mullard CV131/6CQ6
 
These are very nice sounding tubes with a laid back character that feels like you’re sitting a few rows back from the center of a concert hall. Keeping with the typical Mullard family sound, these tubes emphasize warmth and fullness, a characteristic I find very complimentary for my collection of Grado headphones. Bass quality is excellent in terms of texture and nuance, this is toe-tapping bass without being overpowering. Overall these are very nice tubes with no obvious faults and much to love.
                Bass: 17
                Mid: 18
                Treble: 16
                Detail: 14
                Soundstage: 16
                Total: 81/100
 
2.4 Mullard M8161/CV401
 
Focus is the word. This mil-spec version of the Mullard CV131 is one of the best sounding EF92 tubes around. It brings to the table all of the fine qualities of the Mullard CV131 and adds to it a background so extraordinarily quiet you will actually notice the silence between notes. A low noise floor lets details stand out, and music with female vocals in particular is presented with a magical sense of focused intimacy that draws you in and makes you feel as if the singer is standing right next to you, singing into your ears with all the inflections and emotions preserved. Overall this tube is well balanced and ‘audiophile’ sounding and is one of my personal favorites.
                Bass: 19
                Mid: 18
                Treble: 19
                Detail: 20
                Soundstage: 19
                Total: 95/100
 
2.5 MWT W77
 
This rare and little known tube made by Marconi Wireless Telegraph sounds like no other in my collection. Otherwise uninspired with noticeably loose bass that colors the mid-bass and vocal frequencies, this tube’s special redeeming feature lies with its dramatically SPACIOUS presentation of soundstage which makes those close mic’d recordings (you know the ones you can’t bear to listen to anymore ever since you upgraded your headphones) enjoyable to listen to once again. Recommended for close mic’d rock and roll and overtly forward classical music. 
                Bass: 16
                Mid: 13
                Treble: 14
                Detail: 10
                Soundstage: 19
                Total: 72/100
 
2.6 United Electron EF92
 
This is one of my favorite EF92 tubes besides the M8161. A great jazz tube with clear highs that’s well extended to the upper registers combined with outstanding soundstaging giving a sense of environment beyond the music.
                Bass: 16
                Mid: 16
                Treble: 18
                Detail: 18
                Soundstage: 20
                Total: 88/100

 

[Dept_of_Alchemy]

 

[size=18.0pt]3. [/size][size=18.0pt]EF95 FAMILY[/size]

 
3.1 Overview
 
The EF95 family is the most versatile and widely available of the three families of tubes reviewed in this guide. I recommend beginning users to start tube rolling within this family because it has the most variety of manufacturers and models to choose from, and gives you the most sound for your money (particularly starting with the 6ZH1P-EV). Little Dot Mk-series amps are factory configured to use this family and the Darkvoice 332/3322 amps also use this tube exclusively.
 
Also known as: EF95, 5654, 6AK5, 6J1, 6ZH1P, 403B, CV850, M8100, 6DL5, DP61, PM05
 
3.2 Amperex 5654
 
First impression of these tubes came off a bit shy sounding at the 10 hour mark. With about 50 hours of burn-in time, the sound eventually matured and developed a good amount of detail without being overly bright or edgy. My main reservations about these tubes are its lack of bass ‘oomph’ and its upper-mids is too forward sounding and smothers the top-octave ‘air’, robbing the overall sound of a sense of immediacy.
                Bass: 12
                Mid 18
                Treble: 15
                Detail: 16
                Soundstage: 12
                Total: 73/100
 
3.3 Chinese 6J1
 
Manufactured at the Shuguang factory in China, these tubes are sometimes used as stock driver tubes for lower end LD amps and can be found cheaply from various overseas sellers on eBay (usually not matched). Sonically, these tubes are too ‘bright’ from the beginning, bass is muddy and undefined and vocals are masked by overpowering treble notes (which improves a bit as the tubes burn in), but in the end these tubes failed to approximate the ‘Hi-Fi’ sound and just do not do justice to the otherwise great sounding LD amps.
                Bass: 10
                Mid: 11
                Treble: 13
                Detail: 13
                Soundstage: 12
                Total: 59/100
 
3.4 Collins 6AK5
 
These hard to find tubes have smooth and full bodied bass, somewhat recessed mids and a good sense of imaging.  They have a peculiar ‘congested’ sound during complex passages such as full orchestral music and suffers from a smidge of sibilance.
                Bass: 16
                Mid: 13
                Treble: 15
                Detail: 12
                Soundstage: 15
                Total: 68/100
 
3.5 GE 5654
 
GE is one of the most widely available manufacturer of the EF95 family of tubes and comes stock with many LD amps.  Sound quality is average with a more upfront in-your-face sound.  Listening to the notoriously close-mic’d Jack Johnson’s “On and On” can be a claustrophobic experience with these tubes due to its up front qualities but chamber music is complimentary.
                Bass: 12
                Mid: 15
                Treble: 13
                Detail: 13
                Soundstage: 10
                Total: 63/100
 
3.6 GE 5Star 5654
 
These hand-picked broadcast quality tubes are surprisingly unlike the standard GE tubes. I like these tubes for their evenness and silence which really lets you focus your mind on the music, and their soundstage is even and expansive as long as you have a matched pair.  I find myself tapping my toes listening to music with these tubes.
                Bass: 17
                Mid: 16
                Treble: 17
                Detail: 19
                Soundstage: 18
                Total: 87/100
 
3.7 GE JAN5654W
 
These military spec tubes really have a sense of quality construction about them.  The first thing I noticed about these tubes when they arrived is just how neat and solid its internals look.  Their sound doesn’t disappoint either with incredibly good treble extension, clarity and quietness that reminds me of the GE 5 Star tubes reviewed above.  Its upfront sound is in keeping with the GE family sound, violins sounded desperately beautiful with these tubes. In the bass department, PRAT and OOMPH are the first adjectives that come to mind. Compared to the Mullard M8100, these tubes are airier and their bass not as soupy.  These tubes also have exceptionally clean vocal and lends itself well to modern jazz recordings such as Eva Cassidy’s “Live at Blues Valley” where the reverb of the room is clearly audible.
                Bass: 19
                Mid: 19
                Treble: 20
                Detail: 18
                Soundstage: 17
                Total: 93/100
 
3.8 Mullard M8100 / CV4010
 
The Mullard house sound is much warmer compared to the GE tubes reviewed above. The warm tone is especially complimentary to female vocals where sultry voices such as Norah Jones and Dianna Krell’s come across as positively seductive. With rock music, the full body bass has a visceral impact.  These tubes don’t have the sweetest treble of the EF95 family (that title goes to the 6ZH1P-EV), but they nevertheless manage to give the music a sense of presence and body. Trumpets and strings unfortunately don’t have the most prat or the most natural decay but these are sins of omission that I could happily live with.
                Bass: 20
                Mid: 20
                Treble: 18
                Detail: 18
                Soundstage: 18
                Total: 94/100
 
3.9 RCA 5654 (Black Plate)
 
The first thing you will notice about these tubes is how solid their bass response is.  If Mullard bass is too warm for you then definitely give these RCA black plates a try.  RCA cranked these out by the thousands back in the day, and in my experience they are very easy to find.  These tubes have a nice soundstage presentation and are extraordinarily good for classical music.  The sound has good balance overall and improves with burn-in.  They have the great quality of getting out of the way of the music and are a great middle-of-the-road choice.
                Bass: 19
                Mid: 17
                Treble: 16
                Detail: 19
                Soundstage: 16
                Total: 87/100
 
3.10 Voshkod 6ZH1P-EV
 
I first became intrigued about these Russian tubes when several head-fi members began posting wildly contradictory comments about them – so dissimilar were people’s impressions about these tubes that I just had to find out for myself what they really sound like.  After some research I discovered that many versions of this tube were manufactured in various factories in the former USSR, and by far the best sounding version is the Voshkod 6ZH1P-EV which was made for cold war rockets.  I got my matched pair from Yen Audio and first impression out of the package proved that in keeping with its military heritage, these tubes are some of the most solidly constructed tubes I’ve ever encountered. Sonically, these tubes pleasantly surprised me with their stunningly clear and transparent treble and authoritative sounding bass that compliments my HD650 as well as my Grados.  Vocals are similarly impressive with a level of realism that is what I love about the ‘tube sound’. These are my favorite EF95 tubes.
                Bass: 19
                Mid: 20
                Treble: 19
                Detail: 19
                Soundstage: 18
                Total: 95/100
 
3.11 Sylvania 5654
 
Reserved sounding tube at first and needs burn in. Good balance of frequency extremes and good imaging. Effortless sound quality during complex passages, good decay of cymbals.
                Bass: 16
                Mid: 15
                Treble: 17
                Detail: 18
                Soundstage: 18
                Total: 84/100
 
3.12 Sylvania Gold Brand 5654
 
These are the best tubes Sylvania made and are easy to identify as they have golden pins. They are warmer sounding than GE and RCA tubes, and have slightly better vocal than Mullards but sacrifice some bass performance. My matched pair required a lot of burn in and sounded much better after 20 hours or so. The thing that stands out about these tubes is their razor sharp 3D imaging, and their outstanding balance of detail and warmth without compromising either quality.
                Bass: 16
                Mid: 19
                Treble: 18
                Detail: 20
                Soundstage: 18
                Total: 91/100
 
3.13 Tung-Sol 6AK5
 
The famed Tung-Sol has always been one of my favorite vacuum tube brands since day one of my tube rolling journey.  The Tung-Sol 6AK5 didn’t disappoint, offering a smooth laid back sound. It has the richness and sweetness of the Mullard midrange but with better frequency extension in the top end. If Mullards are too warm for you then give this tube a try.
                Bass: 18
                Mid: 18
                Treble: 17
                Detail: 19
                Soundstage: 19
                Total: 91/100
 
3.14 Western Electric 403B
 
The WE 403B has long been the standard bearer of 403B tubes.  Unfortunately they suffer from microphonic issues and all 3 of my matched pairs have audible chime-like ringing during power cycles.  I really wanted to like them as WE has a good reputation, but extended listening to these tubes always caused fatigue to my ears due to a high frequency glare and sibilance.
                Bass: 12
                Mid: 12
                Treble: 08
                Detail: 15
                Soundstage: 10
                Total: 57/100
 
3.15 Westinghouse 5654
 
These tubes really like instrumentals and has great PRAT with guitar and piano recordings.  Vocals are recessed sounding and anemic sounding bass make these a bad pairing for rock 'n roll music but they have their charm with jazz recordings.
                Bass: 10
                Mid: 12
                Treble: 17
                Detail: 17
                Soundstage: 18
                Total: 74/100

 

[Dept_of_Alchemy]

 

[size=18.0pt]4. [/size][size=18.0pt]POWER TUBES[/size]

 
4.1 Overview
 
The power tubes reviewed in this guide only applies to the current production Mk series amps. Unlike their impressive flexibility with signal tubes, most current production Little Dot amps can only accept 6N6/6H6P power tubes with the exception of the MkIV which can accept the 6H30Pi (for clarification refer to this chart).  It is important for the longevity and performance of your amp that the power tubes you use are matched pairs, otherwise it is common for power tubes and other components in the amp to fail pre-maturely due to badly matched tubes.  I have had several power tubes fail within 100 hours of use due to matching issues.
 
 

 

[Dept_of_Alchemy]

 

[size=18.0pt]5. [/size][size=18.0pt]CONCLUSION[/size]

 
5.1 Can’t Decide Which Tube to Buy?
 
To Little Dot’s credit, their Mk-series amps have an impressive number of tube rolling options and there are more than a few very informative threads dedicated to this topic.  I would recommend anybody interested in upgrading their stock tubes to take advantage of our collective knowledge and take a look at those threads.  Occasionally I have received PMs from new members who are overwhelmed by the sheer number of tube rolling options, and asked for my recommendations so they can stop reading forums and get back to listening to their music.  So here’s my short list: I would recommend the Voshkod 6ZH1P-EV as the best place to start as it is a clear upgrade from the stock tubes, followed by the Mullard M8083 for its impressive treble clarity and top-octave ‘air’ (provided you have matched power tubes). The RCA 5654 (black plate) is also a wonderful option for its solid all-around performance, great bass response and availability.
 
5.2 Tube Sellers
 
I’m very picky about whom I purchase my tubes from, particularly about how they match and test their tubes as well as warranty periods. The following is a quick list of tube sellers that I have personally dealt with and have been happy with. There are certainly many more just a Google search away.
 
Yen Audio
TubeDepot
VacuumTubes.net
Thetubestore.com
 
5.3 Useful Links
 
Intro to Tubes: http://www.head-fi.org/forums/f5/new-improved-tube-faq-newbies-119389/
Little Dot Official Site: www.littledot.net
Official Little Dot Dealer: http://shop.ebay.com/davidzhezhe/m.html?_trksid=p4340.l2562
 
 
----------------------------------------------------------------------------------------------------------------
Version History:
1.0 - 07/22/2011 - original post
 

 

[Dept_of_Alchemy]

.

 

[FrankWong]

This. Is. Amazing. 

 Thanks for the reviews, my impressions are mostly in line with what you said. Gonna find some more tubes to roll....

 

[AlexRoma]

Thanks for this guide. The %-tage measurement is a great idea indeed. Very good structure and user-friendly guide.
 
I have a question though.. I own an MKIII. Would a power tube upgrade ( 6H30** series ) deliver more horse-power, not just better SQ  ?
 
I need a little more power for my 600ohm bayers, so I have to decide, am I spending ~70$ on super-tubes, or am I selling the amp as it is, add another 70$ and buy the darkvoice 336 instead. 

 

[zero7525]

Very nice assessment! Can you do a rating on the WE408A too?

 

[shipsupt]

Great post. Nice to see all this information summarized in one place. Thanks.

 

[Dept_of_Alchemy]

Quote:

Thanks for this guide. The %-tage measurement is a great idea indeed. Very good structure and user-friendly guide.
 
I have a question though.. I own an MKIII. Would a power tube upgrade ( 6H30** series ) deliver more horse-power, not just better SQ  ?
 
I need a little more power for my 600ohm bayers, so I have to decide, am I spending ~70$ on super-tubes, or am I selling the amp as it is, add another 70$ and buy the darkvoice 336 instead. 

Thank you for your kind words. Looking at their data sheets, the stock 6N6P tube draws 750mA compare to the 6H30Pi which draws 850mA heater current, which is not much of a difference. Empirically I never noticed a volume difference between the two (I'm using matched Novosibirsk 6H6P-I in my amp which sounds good with my 300ohm Sennheisers). To get the most volume have you tried setting the jumpers to their highest gain setting (off/off)? I think the jumper settings would have the most impact for your situation than any power tube upgrades which is usually done to improve sound quality.
 
- DoA
 

 

[TMRaven]

Quote:

Thanks for this guide. The %-tage measurement is a great idea indeed. Very good structure and user-friendly guide.
 
I have a question though.. I own an MKIII. Would a power tube upgrade ( 6H30** series ) deliver more horse-power, not just better SQ  ?
 
I need a little more power for my 600ohm bayers, so I have to decide, am I spending ~70$ on super-tubes, or am I selling the amp as it is, add another 70$ and buy the darkvoice 336 instead. 

Are you saying they're not being driven to their optimal dynamism, or their volume level isn't as high as it should be?  I find the volume level part hard to believe, as I own the weaker MKII and on the highest gain setting, I rarely find myself putting the volume knob over 20% with my 600Ω 990s.  The volume knob was even lower when I had the stock power tubes in as well (6n6?) compared to my current ones (6H6N)
 
 

 

[AlexRoma]

Thanks for replay, guys.. Sorry for not mentioning the gain I had used before. It was mine mistake. In fact I had made everything possible to rise the volume. I've set gain 10 (off, off) from the very beginning , used ASIO for transport (which turns off OS mixer, rising the volume to it's maximum level). Looks like my crappy DAC/AMP (AudioGD NFB11) simply gives too little volume on RCA outputs (low gain), and I will not turn High Gain on, cause, I get noticed decrease of DAC fidelity. I do never use DT880's below 50% cause it's too boring, bass tends to disappear at all below 50% . I get optimum performance only when raising the bar to 65-70% (one o'clock). I can stand this volume level for a whole day, so I don't consider this level fatigue loud. 
 
Little Dot MKIII is capable of pushing my DT880 (600) to pretty high volume indeed (on 90-100% load) but when it's pushed over 65% (1 o'clock), the background isn't silent any more.. There is a clear Hissss sound , never noticed below that level. I just want extra 100 mW so that I have never had to rise my volume higher then 50%. My power tubes are stock (6N6P), drive tubes - Mullard M8100 CV4010 . 
 
I don't know which is the optimal dynamism of DT880's. I've listened these through 3 different amps (MKIII , M3, NFB11 stock amp). They all sound different but there were no night / day difference so that I could clearly point the right performance, or the one which is below optimum. 
 
Update : PROBLEM SOLVED buy repalcing power tubes with backup 6N6p pair. Looks like the were some true matched tubes previously, if both were running same half-dead.

 

[Impulsive]

awesome test!
I knew Vohskods are hidden talent!
As soon as i collect some money i will buy pair and since you said that tung-sols are a bit darker than Mullards M8100, i have to give them a try too.
How about Voshkod vs M8100, warm vs dark?