Bottlehead Forum

The backstory:
We all know that the "best" 6080/6AS7 hands down are the Western Electric 421A and the GEC Curved Brown Base 6AS7G. These come up often on eBay, and bid prices often go for $120-$150 a NOS piece. However, there's always going to be one desperate nook that would drop their wallet to have it. Let's put this into perspective. The 421A NOS would fetch around $120+, $250 in factory box apiece. The GEC 6AS7G handily fetches $250 apiece as well. The next closest tube to these super tubes, the Tung Sol 5998, are reliably found for $75+ apiece, $110 if boxed. Personally, I would not pay more than $120 for a single tube, input or output. For me at least, it just doesn't make sense to run a tube that costs as much as the Crack itself. Tubes for sale on TaoBao will not be considered.

The aim of this guide is to narrow down the "best" affordable "premium" 6080/6AS7 tube type that isn't a 421A or A1834 which could reliably found for sale. Rare types will only be included as a reference. Any other tubes not listed here would not be considered as a "premium" tube. A few standard types have been included as a reference point.

The give you an idea of how each tube sounds, the Tung Sol 5998 will be used as a reference to demonstrate what the lesser tubes lack in sonic qualities. The stock generic 6080 that came with the kit will be used as reference to demonstrate what each "premium" tubes does better. "Generic 6080" refers to any other 6080 not listed here that are in the family of 6AS7/6AS7G/6AS7GA/6080/6080(WA/WB/WC)/5998A etc...

Disclaimer: Your experience and mileage with these tubes may vary. My Crack is modified which may affect the sound quality of each tube. (See Mods below)

THE LIST
I.a) GEC Curved Brown Base 6AS7G A1834 CV2523
I.b) Western Electric 421A
I.c) GEC Straight Brown Base 6AS7G A1834 CV2523

II.a.i) Tung Sol 5998
II.a.ii) Tung Sol 421A
II.a.iii) Cetron/Tung Sol 7236
II.b.i) Bendix 6080WB with slotted graphite cross columns
II.b.ii) Bendix 6080WB with solid graphite cross columns
II.b.iii) Bendix 6080WB with solid graphite columns
II.c) Bendix 6080WB
II.d) Mullard (Telefunken/Valvo/GEC) 6080WA CV2984
II.e) Sylvania 7236

III.a) Sylvania Gold Brand 6080
III.b) Tung Sol Chatham 6AS7G
III.c) RCA 6AS7G
III.d) Tung Sol 6080 or 6080WA

Tubes not included in this review:
6H13/ECC230 (Various labels: Philips/Amperex/Svetlana/Winged-C)
5998A
6AS7GA
Sylvania 6AS7G
Any other 6080WA/WB/WC variant not listed

Detailed review:
The ones underlined are tubes that I have or previously owned and are reviewed personally. Red indicates a reference quality tube and are one of the top tubes most sought after. Brown indicates a reference tube that do not cost big $$$ otherwise and are highly recommended. Green indicates a rare tube and are highly sought after.  Now, I've sorted the tubes into 3 tiers. It's not that their sound falls into 3 tiers, but their prices conveniently falls into 3 separate tiers entirely. Prices are based on tubemaze and other reliable eBay sellers or reputable online sellers as well as any known local retail prices.

(NIB: "New-in-box" New old stock with original factory box. NOS: New old stock, with tested NOS values. Prices for used tubes will not be listed as they are all over the place)

Reference stock tube: Stock American 6080 Tube (Labelled GE)
Nothing too special about these. Good quantity of bass and wide soundstage. Does not excel in any particular quality, as such it lacks the detail and refinement of the premium tubes. It is actually a fairly neutral tube but as a result, doesn't do musicality and is lacking in analog warmth.

Tier I
I.a) $250 (NIB) / $150 (NOS) GEC Curved Brown Base 6AS7G A1834 CV2523 (Also labelled Osram/MWT/STC) [Bottom cup/pan/halo getter]:

The "Super Tube", the "Holy Grail" of all 6AS7Gs. The GEC 6AS7G is very balanced in each aspect, good micro detailing and extremely analytical. The soundstage is very spacious, and has lots of air. Layering is very good and is probably the best of all British tubes. The differences between the curved and straight base are near indiscernible, so there’s no need to extra big bucks for the curved brown base in particular.

I.b) $250 (NIB) / $100-$180 (NOS) Western Electric 421A [Dual Bottom D/Halo Getters] (Labelled "5998/421A" in earlier 50's production):

THIS IS NOT A RELABELED 5998 (See construction features below).
(See Tung Sol 5998 below) Contrary to popular belief, the 421A is not just a cherry picked 5998 for matched sections evident from the different construction. The 421A is basically an uber 5998 with better dynamics, more air, transparency and soundstage imaging and presentation. Whether the refinements over the 5998 are worth the premium ($75 at average) are up to you.

Closely matched sections with much higher tolerances than that of the 5998 means that this tube is guaranteed to have balanced channel levels when running an OTL amp with a single power tube. However, do note that a very well matched 5998 is nearly identical in sound to the 421A.

The 5998 and 421A are distinct to any other tubes in the 6AS7 family but are not identical. These are the construction features specific to the 421A:
-Always have dual bottom halos or D getters with spiral wound "pigtails" filament wiring >>> 5998 have straight filament wiring and cleartop 5998s are very rare.
-Electrical data: The 421A has slightly higher gain than the 5998 from published electrical datasheets
>> Grey plates are NOT exclusive to the 421A. Photos of various 421A and 5998 manufactured within the same period are identically black or grey plates respectively

The tubes listed below are often mistaken to be a 421A:
-Sylvania, Chatham, Svetlana 6AS7G have dual bottom getters. They do not have domino plates and are not the 421A.

I.c) $200 (NIB) GEC Straight Brown Base 6AS7G A1834 CV2523 (Also labelled Osram/MWT/STC) [Bottom cup/pan/halo getter]:

Slightly inferior in sound to the curved brown base ever so slightly that they are near indiscernible but otherwise identical in sound.

Tier II
II.a) The 5998 sound
The tubes listed below belong to the 5998 family of tubes. Do note that the 5998A is NOT the Tung Sol 5998 and does not have any sonic resemblance with the exception of the 7236. 5998s are ST shaped and were only produced by Tung Sol.

II.a.i) $110 (NIB) / $75 (NOS) Tung Sol 5998 (Chatham 2399/Tung Sol 6520/IBM 5998/Cetron 5998) [Single or Dual Top D Getter (50-60s') or Bottom D getter "cleartop" (50s') or Bottom and Top Getters (60-70s')]:

The "reference" tube for all 6AS7 tube types, this tube is very linear, detailed and has very good bass. If I were to say, along with the "super tubes" up there, the biggest difference with the bog standard 6AS7G tube types is that there is an entire layer/dimension of music added that is missing from the standard ones.
-The 5998/421A are easily distinguished from their dimpled "Domino" Plates.
-Some of the 6520's have the standard plates. The equivalent Tung Sol 6520 are built with the 5998 domino plates.
-Tung Sol also made 6AS7Gs with cleartops. Do not confuse this with the 5998 and check that it has the domino plates.
-The 5998A is NOT the 5998. The 5998A could be labelled as any other American manufacturer and do not have the domino plates. The 5998 was only made by Tung Sol[/size]

II.a.ii) [RARE] $80 (NOS) Tung Sol 421A [Dual D getter]:

Basically it's a Tung Sol 5998 labelled "421A" and has the black 5998 plates. Do not have one myself but pretty sure it's either the same tube as the 5998 with different getters or a 5998 with 421A specifications without the WE 421A construction differences.

II.a.iii) [RARE] $75 (NOS) Cetron/Tung Sol 7236 [Dual Halo Getters]:

The 7236 is a computer rated 5998A but should sonically sound similar to the 5998. This specific 7236 has zirconium coated grey box plates. Similar to the 5998 sound abeit more linear, tighter bass and more dynamic. Basically a "faster and controlled" 5998 but at the expense that the bass doesn't go as deep. This tube is glorious listening to vocals and is probably the most controlled and "best" mid-centric tube of the 5998 pack.
II.b) The Bendix 6080WB Graphite Plates
Unlike all other 6AS7 tube types, these had solid graphite COLUMNS and not plates and are very heavy duty. They have ruggedized construction features such as extra supports and copper posts not found on other 6080 tubes. Regardless of branding, these were all manufactured by Bendix. These are a really good buy and an excellent alternative to the 5998

II.b.i) $75 (NOS) (Bendix/Tung Sol label) 6080WB with slotted graphite cross columns [Dual D/halo getters]:

Very live sounding, dynamic and surreal. Instrument separation is superior to the 5998. However, paired with the E80CC I find that it separated the instruments too much leading to loss of coherence. Upon extended listening, I realized that this was a result of the soundstage going deeper than before. The bass was tight and puinchy . If there is any easier way to describe this tube, this tube takes the linearity of the Tung Sol 7236 and adds deeper and stronger bass much more air. Will try different pairings of input tubes later to see if I could get a better sound than the 5998. It is true that this tube is probably better than the 5998. I would gladly stock up extras of these as they are quite plentiful although they do cost the same as the 5998 as if now.

II.b.ii) $75 (NOS) (Bendix/Tung Sol label) 6080WB with solid graphite cross columns [Dual D/halo getters]:

Should be similar to the slotted columns but I can't say unless I have one myself.

II.b.iii) $40-75 (NOS) (Bendix/Chatham label) / $35-75 (NOS) (Tung Sol label) Bendix 6080WB with solid graphite columns [Dual D/halo getters]:

Nearly identical in sound to the slot cross columns as I find it strangely, to be slightly inferior. I do not know if it's my ears or this particular tube that I have but it sounds like this version isn't as fuller bodied as its more expensive brother. This was compensated well with a more musical tube though, I had a rare RCA 12BH7A with foil D getter paired with it and it sounds fantastic at the expensive of some air and soundstage depth. Unlike the slot cross columns, I find the sound wasn't as full leading to a loss of coherence for orchestrals and string quartets due to excessive separation. If there was a better way to describe this effect, it is the lack of that concert hall "reverb". I would gladly stock up extras of these but unfortunately, this is not the perfect tube and would prefer the fuller bodied 5998 or the cross columns 6080WB more. Couldn't expect too much for nearly half the cost.


II.c) [RARE] $50 (NOS) Bendix (Raytheon) 6080WB [Dual Halo Getters]:

This is a strange tube, because tubemaze classifies this as a "5998" tube even though it is not related to the 5998 at all. It features the same ruggedized construction design of the graphite variant 6080WB but otherwise looks identical to any other 6080. Closer inspection also reveals that the plates have dimples. I doubt if it sounds similar to it's graphite brothers though.

II.d) $50 (NIB) Mullard (Also labelled as Telefunken, Valvo and GEC) CV2984 6080WA [Dual Halo Getters]:

Marketed as having the same sound as the GEC A1834/CV2523. For a fraction of the cost, this tube has 80% of the GEC Brown Base's sonic qualities. Mainly the same sound but less micro detail and not as analytical and weaker instrumental separation. Do not be fooled, there is an eBay seller selling these for well over $250 a pair. They are not worth that much. Listed as rare due to infrequent sales online. Readily available at a local NOS tube store in Hong Kong though for $60.

II.e) [RARE] $50 (NOS) Sylvania (CEI) 7236 [Dual Halo Getters]:

Same as the above but looks indifferent to the standard 6AS7. I believe this is the "7236" people are talking about that does not sound any different to the standard ones. It probably is just a relabelled Sylvania Gold Brand 6080 (See below). There are also some Sylvania metal base versions with a single halo getter, however that is rarely seen.

Tier III
III.a) [RARE] $20 (NIB) /$10 (NOS) Sylvania Gold Brand 6080 [Dual Halo Getters]:

"Unlike other 6080 tubes that have very tight sound, this is more relaxed. Compared to other tubes in 6as7 family, this is the most liquid tube." - Nikolay Sokratov.
This tube does not deviate too much from the standard 6080, but has the liquid smoothness and musicality typical to any Sylvania manufactured tube. Does not have the detail of any of the exotic 6AS7 tubes but definitely excels in musicality. I would very much prefer this over the RCA 6AS7G as it does not have that thick bass but unfortunately these are very hard to get your hands on for a good price. Currently sells for $80 (NIB) for a single tube from an Italian seller on eBay which is IMO a complete ripoff. Shouldn't be paying for more than $20 apiece. Occasionally comes up as used tubes but still rare. I got lucky and scored a bunch of untested but NIB NOS by chance from eBay. You really shouldn't be paying more than $20 for these since they are quite literally just cherry picked standard 6080 tubes but they are rarer than the WE421A and TS5998 as of now.
This is perhaps the best poorman's 6080, yet these are one of the few tubes I'd stick to listening along with the TS5998. Do note that unlike the other Sylvania 6AS7GAs, these are actually labelled "Gold Brand 6080"

III.b) $30-40 (NOS) Tung Sol Chatham 6AS7G [Dual Top/Bottom D getter](Black Plates):

Compared to the Tung Sol 5998, the bass is not as thick and lacks the soundstage and air. Unlike the 5998 which is more linear, the Tung Sol 6AS7G is brighter sounding leading to a clearer and more focused sound in the higher frequencies. Not as warm sounding as the 5998 but is very sweet sounding with female vocals.

III.c) $20-40 (NIB) /$10 (NOS) RCA (and Various labels) 6AS7G [Top or Bottom D/Halo getter](Black Plates):

The bog standard 6AS7G. Very musical, has that signature RCA house sound that's warm and thick on the sounding bass. This is a very balanced combination with the cleartop RCA 12AU7A due to the early treble rolloff. However, as it is the "bog standard" tube, it doesn't stand up against anything more expensive and is missing the layer of sound and detail of the 5998. Tried pairing it with the Tungsram E80CC. Didn't help much though. Avoid using the grey plates version. The RCA 6AS7G is already as cheap as you could get.
Disclaimer: Many claim that this tube is noisy. My particular tube was dead quiet. Your experience may vary.[/color]

III.d) [RARE] $20 (NOS) Tung Sol 6080 or 6080WA (Westinghouse labeled):
In comparison to any other generic 6080 tube, the Tung Sol 6080 delivers far better bass punch and is thunderous when needed. Although it isn't much different to the generic 6080, somehow the Tung Sols just have "soul" and delivers musicality not present in the generic bunch.
This was once the stock kit tube. Reason why I listed it as "rare" is because you honestly can't buy it anywhere. If there's a tube out there for equal or less the same price as the standard straight bottle 6080's that's better, it's definitely the Tung Sol tubes. That is why these had disappeared as well.

Hope this helps.


Test Setup:
Bottlehead Crack
Speedball Upgrade
-Mundorf TubeCap 100uF output caps w/Mundorf SGO 1uF coupling
-Mundorf TubeCap 220uF power cap w/Mundorf SUP8 2.2uF coupling
-Goldpoint 100K Mini-V Stepped Attenuator
-Mundorf SilverGold/DHC Nucleotide wires for signal paths
-Kimber TCSS for non signal paths
-Teflon Tube Sockets
-Vampire RCA Sockets

Input tubes used:
-Tungsram Steel pins E80CC: This is by far the most linear input tube abeit its bass rolloff. This increases the perceptibility of the bass characteristics of the output tube. This is my reference input tube for more objective listening.
-Russian 6N8S/6H8C Black Plates: One of my more affordable premium 6SN7, as I do not want to pull out my roundplates 6SN7 or hole plates 6N8S/1578 for the purposes of this review. Neutral sounding similar to that of the Tungsram Steel pins E80CC this is my more recent reference tubes as it offers slightly "more" and is less prone to that bass rolloff the E80CC exhibits.
-Sylvania VT-231: A good affordable 6SN7 being in the middle ground but comparatively musical sounding. Offers decent technicalities but notwithstanding compared to the roundplates 6SN7

Source:
HRT MusicStreamerII+

Headphones:
Sennheiser HD650 with J.A. Harmonic Quadraweave OCC Copper cabling

I have an Amperex 6AS7G.  It looks very similar in construction to a 421A.  You ever seen or heard one of these tubes?

I have 3 5998's, two variations.   One is a grey plate, dual bottom D getter.  The other two are black plates, dual top D getter.  Sonically, they are the same.   I had another variation with both top and bottom getters that was noisy.    I have remained skeptical about any signifigant differences (sonic) between the 421A and the 5998 because of several reasons related mostly to internet "research".  But, I fully admit to never owning a 421A so I could very well be wrong.  But your photo of the Tungsol labeled 421A doesnt tend to change my thinking.   The biggest "issue" that I have is that Ive seen several of both the 5998 and 421A tubes with different internal contruction from one another, respectively.   The 5998's that I have/had that are different internally all sound essentially the same so it leaves me plenty skeptical enough to not have any desire to spend the money on a 421A.   Again though, I could be wrong and will probably never know for sure unless a 421A basically dropped in my lap.

Very nice post BTW.

I have 3 5998's, two variations.   One is a grey plate, dual bottom D getter.  The other two are black plates, dual top D getter.  

It appears that I was wrong about the plates: WE 421A had grey plates in the 50's and black plates in the 60's onwards. In other words, the 421A and 5998 are otherwise identical in plate construction as the 5998 was indifferent in the given production periods. See photo

Although we could now be sure that the Tung Sol 421A is otherwise just a rebranded 5998 with 421A specifications.

I agree with you Nick, without owning a 421A it's impossible to be certian if there is any signifigant sonic difference from the 5998.   Thats why all I can say is that I remain skeptical.  But I really appreciate you posting that Tungsol labeled 421A.  That kinda adds fuel to my own fire      I wish that top and bottom getter variation I had was a good tube.  I'd like to have 3 variations of them just to have them,  even though I couldnt hear any real differences.   

I have mentioned previously, what Paul has stated.   That maybe the WE 421A is a selected 5998 with some internal contruction differences.   Well, atleast for some of them, the Tungsol labeled 421A murkys the waters some more.   But the bottom O getters are the most obvious from your pictures and others I have seen.   Still, that doesnt necessarily make them signifigantly different, sonically.   I never really chased a WE, when I have seen them for sale it has been at too steep a price for me and it's likely to remain that way.   I know most of the folks who have one proclaim the WE is better but of course human nature has to be accounted for so I still remain skeptical.  But fact still remains that without one myself I will never know for sure.

I bet a lot of people are kicking themselves for literally just throwing away their tubes now that there is a market where people will pay tons of money for such things.

I don't think anyone would do that... a little research on eBay is all you need to do if your dead tube is worth someone else' fortune. I was hunting for rare 421As and A1834s and the prices would always break the $150 barrier regardless... so I turned to hunting for rare 6SN7s for the input side instead. Turns out that, the average price of the "rare" 6SN7s like the Sylvania 6SN7W and British 6SN7s bunch aren't much better...

Well, I would throw out the stock 6AS7 anyways, unless it was the Tung Sol Westinghouse one.

Ultimately, we all have to draw a line for the $$$ barrier for the lone 6080/12AU7 combination we're using in the Crack though

Will they plug in and work? Yes. Is the circuit optimized for them? It certainly was not in mind when designed since the designer chose the 12AU7. So perhaps the tube could work even better than it does.