Decription of output tube types....

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Decription of output tube types....

Post by VelvetGeorge » Thu Apr 07, 2005 5:09 pm

Sometimes some one will say things right and make sense. This is one of them.

George





Awright, here goes. I don't know anything about the pentode/triode difference but I do know what different power tubes sound like, so here's a crummy description of each tube from a player's point of view.

Basically I can distinguish 8 types of end tubes that will fit in a Marshall plexi no problem, each with their own characteristics in sound, feel and response: EL34, 6CA7, 6L6, 7581A, 5881, KT66, KT88, 6550.

EL34: Current-production EL34's are designed to give you that midrange crunch rock music is known for. I never had the pleasure of hearing a new old stock or used old stock EL34 (Mullard) but from the descriptions George has given on this forum they sound warmer and more versatile than the newer EL34's. They are also cleaner with more headroom, which means that when they break up or are pushed by pedals the sound still doesn't get overly compressed or saturated. I find most current-production EL34's to be good only at producing that middy grind. They break up early and most of them tend to get shrill in the high end. The general consensus seems to be that the Svetlana EL34 and the JJ EL34L are the best new EL34's. I personally find the EL34's to be too much of a one-trick-pony for my taste but if you're looking for the classic 70's and 80's rock sound then EL34's are definitely the way to go.

6CA7: The term 6CA7 is often used synonymously with EL34. This is not correct as a true 6CA7 is an American big-bottle version of the British EL34 design. I don't know how it works exactly but from what I understand the 6CA7 is the basic EL34 design but with an added element of the American 6L6 design. The only decent new-production 6CA7 IMO is the GT-6CA7GE (remake of the General Electrics 6CA7 - yes, the one EVH used!). I own some original GE 6CA7's and I would describe them as a cleaner version of an EL34 which is slightly more American-sounding (i.e. more midscooped, less midrange grind, cleaner with more headroom, later breakup). The main feature of the big-bottle 6CA7 is its HUGE dark and tight low end response while still retaining its brightness. This tube is often used by bass players but you guitar players looking for a tube with lots of warm, clean output without sounding sterile might like it too. A very musical tube which is great for use in combination with pedals or heavy preamp gain because of their tight sound and clean headroom.

6L6: The tube you associate with Fender amps. The classic American tube sound: lots of lows and highs, midrange is not so well pronounced. The slightly midscooped quality of a 6L6 gives it its sweet and round 'glassy' character. The 6L6 is less 'forward-sounding' than a British tube like the EL34, yet in return you get a very sparkly tube with bell-like highs. The lows can get muddy when pushed so if you're gonna go for 6L6's in your Marshall I suggest you choose the 6L6GC which has a slightly higher output than a regular 6L6 and will sound tighter due to its increased headroom, especially in the low-end department. Best current-production 6L6's IMO are the JJ's and Svetlana's. I hear the GT-6L6GE (Groove Tubes replica of the GE 6L6) is very good too.

7581A: This is the military version of the 6L6GC, in other words a 'harder' tube (even cleaner and tighter). Expect HUGE low end and sweet, glassy, bell-like highs. This tube has all the qualities of a 6L6, only enhanced due to its bigger headroom. This tube is also favored by bass players but guitarists looking for the American midscooped 6L6 sound with later breakup will love it too. Great for use with pedals or heavy preamp gain to keep your sound nice and tight without it getting muddy when pushed. Unfortunately there's no current-production version of the 7581A on the market today so you'll have to look for NOS ones made by American companies like GE and RCA. They show up regularly on eBay and if you bid smart you can get them for decent $. The 7581A is often called the American KT66 because it's similar in design to that British tube. The 7581A does sound distinctly American (less pronounced mids), tho, whereas the KT66 sounds British (more pronounced mids).

5881: Also called the 6L6WGB and NOT the 6L6GC as they are often referred to. You guessed it, the 5881 is another version of a 6L6. This time, tho, it actually has a LOWER output with LESS headroom. Great for guitarists seeking the classic midscooped American sound with early breakup. Has a tendency to get muddy in the lows and shouldn't be pushed too hard. Not my favorite 6L6-type tube.

KT66: The British equivalent of the 6L6 design. The difference being they eliminated the mid 'kink', that slightly midscooped quality that gives the 6L6 its sweet and round character. KT stands for Kinkless Triode. What the KT66 gives you in return is a more pronounced and wider midrange and more clean headroom. The KT66 is capable of producing a midrange crunch which is similar to an EL34, yet it's considered a more versatile and musical tube. It's the perfect tube if you're looking for a hybrid British/American sound, i.e. the middy grind associated with British amps (Marshall, Vox, Hiwatt, Orange, etc.) coupled with the clean glassiness of American amps (Fender, early Mesa Boogies, etc.). The best KT66 ever is the GEC (Genelex). These go for hundreds of dollars on eBay. Best current-production, according to many, is the GT-KT66HP (Russian-made KT66 designed exclusively for Groove Tubes). Sounds great with pedals.

KT88: The British version of the American 6550 design. Again the mid 'kink' is eliminated, giving you a broader, more dynamic midrange. This tube has HUGE headroom and sounds darker than the KT66 because it enhances the lower frequencies especially. This is why the KT88 is liked by bassists. Guitarists looking for that extra bit of OOMPH! in their sound use either KT88's or 6550's depending on how much midrange they want their preferred sound to have. Again the GEC KT88 is considered the ultimate KT88 which explains their high $ value. Best current-production KT88 is without a doubt the JJ KT88.

6550: If you like the American 6L6 type of sound but you need even more clean headroom than a 7581A then a 6550 is what you want. These tubes sound very stiff and will take any kind of abuse gladly and not even blink an eye, which is great if you're looking for maximum clean headroom in a tube. On the other hand, the 6550 is less musical than its British counterpart the KT88 because of its less pronounced midrange. This causes the 6550 to always respond in a very stiff manner no matter how hard you dig in on your guitar. Bass players love this tube. Most guitarists will prefer the KT88 over the 6550. Yet it's a great tube for guitar if you're into HUGE clean output, especially in combination with heavy preamp gain (Zakk Wylde, Slash). Best current-production 6550 IMHO is the Svetlana 6550-C.

There you have it, Lawrence, the 8 tubes as best I can describe them. One is not better than the other, just different flavors. It really depends on what type of sound you have in mind. These descriptions are meant to help you distinguish between the various power tubes that are available. If I have inadvertenly confused you all the more then by all means describe the type of sound you want out of your amp and I'll try to match it with a certain tube. Maybe some of the others can describe the technical aspects (tube construction, layout, build quality, etc.)?

Mike
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Post by tonejones » Fri Apr 08, 2005 1:33 am

Super cool post George,
Been trying to run into this info for years now!!!!
Let's get going, 'cause there's too much music, too little time!!!!

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Post by Guest » Sun Oct 02, 2005 2:09 pm

Just to make a point clear, the "kinkless triode" has less of a "kink" in its operating curve. This translates to a non-linear AMPLITUDE response and really has nothing to do with FREQUENCY response.

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Post by novosibir » Sun Nov 27, 2005 9:35 am

My highly respect to the initial post! I fully agree to it and I couldn't have said it better with my words, even not in German!

But just let me point out something, to make it a tad clearer:
6CA7: The term 6CA7 is often used synonymously with EL34. This is not correct as a true 6CA7 is an American big-bottle version of the British EL34 design. I don't know how it works exactly but from what I understand the 6CA7 is the basic EL34 design but with an added element of the American 6L6 design.
The 6CA7 is, like all the 6L6 types, not a real Pentode like a EL34. It is a beam power tetrode, what means, that these tube types have beam forming plates inside instead of the supressor grid inside of real pentodes.
KT66: The British equivalent of the 6L6 design. The difference being they eliminated the mid 'kink', that slightly midscooped quality that gives the 6L6 its sweet and round character. KT stands for Kinkless Triode.
Sorry, but this is only "nearly" correct! KT means Kinkless Tetrode - a tetrode with beam forming plates inside like i.e. all 6L6 tube types.
This translates to a non-linear AMPLITUDE response and really has nothing to do with FREQUENCY response.
Right! To make it a bit better understandable:

A REAL tetrode has the behavior, that around about its half power capability (plate current drawing) there is an area in the curve, where its output voltage drops down a bit, although the AC signal voltage to its control grid has been increased. First after further increasing the signal to the control grid, also the tube's output increases again.

So we can say, that all real tetrodes have a "kink" in its diagram's curve.

I very hope, that you all couldt understand my bad English :roll:

Larry (the German)

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Post by tubetramp » Sat Jul 15, 2006 5:00 am

an estute deduction for many sets of ears ,i would have to say that the gt big bottle is far from the original and does not boast durability.i have several 100 watt amps all running at different voltages .the el 34 gets a bad rap by many people for its ,..one trick.the best production without any hesitation from me is the shuguang 06 run of this tube.it is very neutral,yet not sterile.the gts i purchased didnt last long enough to get a good look at.ive used the shuguang for long enough to trust my ears .it steps out of the el 34 mode a bit due to its envelope size .its quite large a purchasing agent i talk to tells me this was the intention .it can handle very powerful amps and does not wash out as quick as most .with good drivers this tube outperforms tesla and seimens in my partridge powered amps the ones with rs type im not quite clear on.remeber that plate current has a ton to do with these animals ,example if i use a quartet at 22 the amp is almost too clean and loud with less mid detail .if i bump up to a 30 set its very close to the sound pattern and flow ,as it was intended to copy....what else but an xf4 ..the most mocked plate design of all time for that tube.also have witnessed its durabitlity first hand.very few ever come back.and they can handle 650 on the plates longer then any other ,i say this in confidence because the super pa im testing some in is 550.typical of the metal panels of the early 70s .i do know what this fellow means about the el 34 .but it does change quick when plate current is address the lower the pc number the louder and cleaner most tubes will go.i find the best grindola is hiding in the 28 to 38 measurement.6l6gc shouldnt be a concern they are available in nos within reason.but if i was to pick one of the newer production ones it would have to be that coin bottom saratov that sovtek copys and fails at.these are easily identified by the diamond logo and otk flying saucer early to late 80s .cheap and hard to kill with tone that most others dont have .drawback or attribute is that they are not quite as loud as 6l6gc but they can go in any 6l6gc powered amp..im lookin at the jj kt77 .ive heard them in duet....yuk two more will come and then i will chuck em in a four banger...output tubes are nothing of any sort without the proper tubes driving them.give me the best pres and the lowend of outputs far better then the other way around..i sell quite a few shuguangs and have had most people come back and buy more .i dont think much of the earlier version of the el 34 the latest gec tooled are very good for the money.i think georges freind has good insight .try the hochimins ..............tt

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Post by VelvetGeorge » Sat Jul 15, 2006 11:02 pm

I have to agree TT. I actually picked up a few quads of Chinese EL34's a while back. But haven't tried them yet. Also got some JJ KT77's. Dan at 65 Corp says they are dynamite. We'll see....


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Post by wdelaney72 » Mon Jul 24, 2006 2:58 pm

TT,
Any thoughts on new production KT88? JJ v. Shuguang?

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Post by Jeff West » Sun Oct 29, 2006 1:28 am

Nice summary, but one other picky thing if you want to be historically accurate. Yes, the larger bottle beam tubes differ in important ways structurally and sonically from the original W. Euro true pentode EL34 as developed by Philips in the late '40s. But official "6CA7" designation was applied to the pentode EL34s sold in N. America at least as early as late 1955, many were sold with no other label, for years and years before the big bottle U.S. 6CA7s (which ironically are often also labelled "EL34" on the glass) were ever developed or sold. Thus it's not the case that a "true" 6CA7 necessarly is a big bottle beam tube, even if that is a notion that's become firmly entrenched on the internet.

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Post by LordAli » Sun Oct 29, 2006 2:47 pm

Jeff West wrote:Nice summary, but one other picky thing if you want to be historically accurate. Yes, the larger bottle beam tubes differ in important ways structurally and sonically from the original W. Euro true pentode EL34 as developed by Philips in the late '40s. But official "6CA7" designation was applied to the pentode EL34s sold in N. America at least as early as late 1955, many were sold with no other label, for years and years before the big bottle U.S. 6CA7s (which ironically are often also labelled "EL34" on the glass) were ever developed or sold. Thus it's not the case that a "true" 6CA7 necessarly is a big bottle beam tube, even if that is a notion that's become firmly entrenched on the internet.
I'm not sure, but I saw somewhere that 6CA7 is beam power tetrode. I know that EL34 is pentode. That's great difference.

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Post by Jeff West » Sun Oct 29, 2006 5:34 pm

Hi LordAli- I don't doubt that you read somewhere that "6CA7" means a beam power tetrode. That's why I posted, because you see that a lot but it's not technically correct. "6CA7" was registered for and applied to original true pentode EL34s for many years before beam tetrode EL34s ever made the scene (as well as after). Under the North American RMA system, the "6" refers to the flament voltage, and the "7" refers to the number of "usable" elements, i.e., that were actually pinned out. The middle letters originally were assigned in different orders depending upon tube type and were often not fully systematic in assignment by the early '50s when "6CA7" was registered.

Incidentally and for interest, in the Euro nomenclature system "EL34" is also not limited to a true pentode! In this system, "E" designates 6.3V heater; "L" designates power output pentode or tetrode; "3" designates octal base. So even from the beginning it would be appropriate to refer to a beam tetrode version as an EL34.

Like I said, for historical accuracy . . . not all that important, but I myself try to say "large bottle beam version" vs. "true pentode EL34", etc., I still see inquiries where someone has, say, a '56 metal base EL34, etc. labelled "6CA7" and thinks it's fake, relabelled, or a beam tetrode.

Jeff W.

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6L6 vs. 6L6GC

Post by guitronics » Fri Jun 13, 2008 4:05 am

The 6L6 was originally made with a metal (steel) casing.You could not see if the tube was lit up. This tube was first made pre 1950's.They were horribly microphonic.

Then again,amplification at the time was mostly very crude.

The 6L6GC stands for "Glass Container" .
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Re: Decription of output tube types....

Post by DerekMessina » Mon Dec 05, 2011 4:41 am

Splendid! Thanks for the information. I've been searching the net for how many times about this and now that I found it. Thank you!

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Re: Decription of output tube types....

Post by Joshabr1 » Thu Dec 18, 2014 6:26 pm

I will add a little. I have tried all current production el34 tubes along with most all the NOS offerings. The shuguang el34 of today stands up with any that I have tried. They are as good tone wise as rft el34s which I like a lot. Mullards or mini watts may sound a touch more musical but its nowhere near the difference in price. If u have a superlead/bass amp try some sino el34s (same as shuguang) they are 15 bucks a piece at tube depot and I have had a dozen quads with no pre mature failures.

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Re: Decription of output tube types....

Post by bill bokey » Fri Dec 19, 2014 2:27 am

I'm with you on that one, I also did a test a while back and have used Shuguang's EL34B ever since. Unfortunately I didn't have all the current production tubes at my disposal back then, only JJ, EHX, newer and older Svet C, the EL34Bs and a set of NOS RFT. The RFT, old Svet C and Shuguang sounded best, close to each other. Then came the latest Svet C (which sounding nothing like the old ones), EHX and JJ.
I buy them at amplified parts dot com (under the Valve Art brand) and they're always well matched.

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Re: Decription of output tube types....

Post by Joshabr1 » Sat Dec 20, 2014 1:10 pm

I actually like them better than rfts. I have 2 quads of rfts in the boxes and quads of sinos in my amps. They get it done in a great way. They sound to me the way a el34 should. Get some spanky ass clean with em to.

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