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We are asked this question multiple times everyday. Bob has personally played and been into tube amps since the early 60's (he’s really old...) Since he started Eurotubes in 1998 we have had the unique opportunity to listen to and play hundreds of different amps. During the first few years we worked with local players here in the studio one-on-one to achieve the best results for each. This gave us the opportunity to play, and more importantly listen, to hundreds of different amps. Thousands of hours were spent trying different combinations of preamp tubes and power tubes to better understand their characteristics and tonal differences, and we continue to do this today. It’s a terrible job, but somebody has to do it!Before we get into methods, reviews and brands we would like to answer some of you who have asked us about the new production Telefunken tubes. Telefunken makes the claim that they are in a partnership with JJ Electronic to produce special “new” Telefunken tubes. Most players who know us understand that we have a very tight relationship with JJ Electronic. We spoke to JJ about this “special partnership” between Telefunken and JJ Electronic. In short JJ didn’t know what Telefunken was talking about. In fact JJ verified that Telefunken is not even a customer of JJ Electronic and said they must be getting them from another dealer! So, you will not find reference on this page to the new Telefunken tubes because they are in fact JJ Electronic tubes. Do yourself a favor and avoid paying more than DOUBLE the price for JJ Electronic tubes by shopping Eurotubes. You will also get the most stringently tested JJ’s on the planet from us.Continuing on, we quickly learned that the method most people used to compare tubes, which is to set the tone controls to one place and leave them for the entire test was inadequate. This procedure does not allow you to get acquainted with the capabilities of the tubes. Some tubes get sweet when treble is dialed in and some get very piercing. It’s very important for tubes to be able to handle added lows, mids and highs without getting flabby, harsh or piercing otherwise you will turn your amp into a one trick pony. We keep a good well matched set of all the currently made tubes such as Svetlana’s, Winged C, Sovteks, EH (sovteks) tungsols (sovtek) mullards (sovtek), EI’s and a host of NOS power and pre-amp tubes such as RCA, Philips, GE, Sylvania, Telefunken, Mullard, Tung-Sols, Brimar, GEC and Amperex to name few for the purpose of comparing them to the JJ line of tubes. The following opinions reflect our opinions and the opinions of the vast majority of our customers, (you can find well over a thousand customer reviews here.) Below is a list of the most common power and pre-amp tubes. POWER TUBES EL84EL346L6KT666550KT88 EL84/6BQ5 Sovtek EL84: This tube has a very harsh mid and upper mid-range. A good way to describe the tone in one word would be to call it "cardboard". They make your amp sound like a big Wheaties box. The low end is flabby and only gets worse as more lows are dialed in. The highs are piercing and brittle. These tubes are just flat and lifeless sounding without much harmonic content. When over driven they get real grainy and the breakup transition is quick and not smooth. Sovtek EL84M: This tube has the same tonal characteristics as the standard Sovtek EL84 and is even more lifeless and less touch responsive. Electro Harmonix EL84: These are sovtek tubes and all the above applies.mullard reissue EL84: These are sovtek tubes as well and are absolutely nothing like the original Mullard EL84's. It should be against the law to muddy a good name like this...EI YUGO EL84: This is a pretty good sounding tube. The problem is finding good ones that are matched. They have nice harmonics and breakup pretty evenly. They don’t have a strong low end but dynamic response is good. The upper mid and highs are this tubes strong points. Nice detail even when distorted. PHILIPS 6BQ5: Even though these are out of production NOS tubes are still fairly available at a decent price. These are nice, warm sounding tubes with good dynamics, nice harmonics. This tube has good definition but is hard to drive into distortion. A nice tube overall but we would use the EI before spending the money on these. They work pretty good for Hi-Fi. JJ ELECTRONICS EL84: This tube has the deepest and tightest low end of any of the tubes reviewed here. The mids are thick and harmonically complex. The highs are sweet and smooth. These tubes are very punchy with a nice chime. When over driven they get nice and thick and do not loose their detail. The break-up is very smooth and linear and they are very responsive to touch. JJ ELECTRONICS EL844: This is a new design for an EL84 type tube. It's not an EL84 that tests low or an EL83 as some of the "all knowing" tube guru's have speculated. This tube was made by JJ at the request of Eurotubes. We wanted a tube that would make less power and would be plug and play for most EL84 amps such Fender Blues and Pro Jr, amps along with cathode biased amps like the AC30's Orange, Dr Z, Budda, Laney, Crate amps to name a few. The EL844 makes 25% less power than an EL84 and will breakup earlier. The tone, both clean and driven is extremely similar. EL34 Sovtek EL34WXT: This tube is an improvement over the EL34R which was a very lifeless tube on a par with the Chinese EL34. The WXT is still harsh in the mids and has a weak low end. The highs are grainy and piercing and when overdriven gets even more harsh and nasally. Tungsol Mullard and Genalex: So now we are also seeing sovtek tubes being labeled as Tung-Sols, Mullards and Genalex... We have auditioned these and while they are slightly different in tone than other sovtek EL34's they still have the mid range and high end characteristics that all sovtek tubes seem to have. Once again it would really be nice if sovtek would stop all the impersonating, these tubes do not sound like the originals and it just muddies the water. Some people will do anything to make a buck... You know what they say, "if it quacks like a duck"... Of course the bottom line with any tube is if you like what it does and the way it sounds then use it. There is no right or wrong when it comes to tone, or the lack of tone.Electro Harmonix EL34: A sovtek tube, but a slight improvement over the EL34WXT with a shallow low end and grainy tone.Sovtek mullard EL34: This is the sovtek EL34B with a slightly different sound but almost indistinguishable from the EL34B so if you're expecting to get the sound of a real Mullard then save your pennies. You would be much better off going with the standard JJ EL34 or the Winged C EL34 which are both MUCH closer to the sound of a real Mullard. It really is a travesty that sovtek tubes are now being made and branded "Mullards". They are sovteks. Nuff said....Groove tubes EL34M: Another Mullard wannabe that falls dreadfully short of the mark. These are chinese tubes and the low end is particularly shallow and the output seems to be off. These actually sound better biased at about 60% of dissipation. Maybe they were trying to get a lower output?Svetlana EL34: These are now sovtek tubes and are about the same quality as the EH EL34 unless you have the older Svet's (the real ones).Winged C EL34: In our opinion this is the best tube that Winged C (the original Svetlana) makes. It’s a little hot on the top end but it has nice harmonics. The low end is solid but not real deep. This tube has good detail and maintains it’s tone when overdriven but I would not say it’s real ballsy. We like this tube better when played clean. The word now is that the St. Petersburg plant has shut down...JJ ELECTRONIC EL34: This tube when played clean is nice and linear. Not top heavy or bottom heavy but nice and centered. Over all this tube is smooth and rich with fairly complex harmonics. The distortion is thick and the detail is very nice even when driven real hard. In fact the harder you drive it the thicker it gets. JJ ELECTRONIC E34L: This tube is very much like the JJ EL34 but it has about 15-20% more headroom. The mids are a bit more complex and it’s obvious that this tube makes a lot of power! Over all it’s a bit tighter than the JJ EL34 which is nice for combo’s or HI-FI where the standard EL34 gives more of a vintage EL34 tone. When over driven the E34L is very ballsy and harmonically rich. It’s not grainy or piercing but thick and creamy. JJ ELECTRONIC 6CA7: Really nice to have this tube available, it’s not as bright in the top end as the EL34 or E34L or the KT77 but it really warm sounding and tames an overly bright amp giving a thick and woolly tone.JJ ELECTRONIC KT77: We had to include this tube in along with the EL34 family. It is not quite a tight as the E34L but tighter than an EL34. The 77's have even a bit more low end extension than the E34L's, real chunky, and they have a nice sizzle in the top end that is not brittle. The clean tone is very fat and full and the crunch has more of a chunk to it and it's very punchy but not quite as aggressive as the E34L nor as powerful. This is one of our favorite tubes just as the original Genalex KT77 is.6L6Sovtek 5881WXT: Let’s see, the first word that comes to mind is "cardboard". As for describing the lows, mids and highs, three words will do it, Flabby, harsh and piercing. This tube is also sold by G.T. and re-labeled GT6L6B. The 5881/6L6WGC is the same tube with a disc base. Sovtek 6L6WXT: This is a better tube than the 6L6GB but it still falls way short of any of the good old standard Philips and RCA 6L6’s. It’s grainy and piercing highs turn to sounding like a swarm of bees when overdriven. Electro Harmonix 6L6EH: Another sovtek 6L6 which is once again slightly better than the 6L6WXT+ but has the same ragged tone.Svetlana 6L6: This is now another sovtek tube that falls short of the original Svetlana in all respects.Winged C 6L6: This is a very nice tube with nice low end, not real deep but much better than any of the sovtek tubes including the now sovtek labeled Svetlana's. The mids are full with a fair amount of harmonic content. The highs are smooth and not piercing. This tube reminds us a lot of the old GE and Philips 6L6’s. It has good detail and the break-up is smooth and rich. The word now is that the St. Petersburg plant has shut down...JJ ELECTRONIC 6L6GC: This tube has the deepest, tightest low end of any 6L6 I have ever tested. The mids are full of complex harmonics. The highs are sweet and down right lush. This tube is the reason Bob originally searched out JJ Electronic when he was in Europe. He imported some of them to test before his trip and was blown away by their tone and performance. His collection of RCA, GE, Tung-Sol, Philips and all the others that sit on a shelf here at Eurotubes in the tube cabinet and are now only used when other players want to A/B them to the JJ’s. When the JJ’s are biased up nice and warm they come incredibly close to that upper mid magic that our Black Plate RCA’s have but the JJ’s out do the RCA’s otherwise and especially in the low end. When over driven the JJ’s get very rich and thick. They don’t squash down and they have excellent definition and detail. Groove Tubes 6L6GE: We really wanted this to be a good tube and they are not bad if you keep them biased at about 55% to 60% of max dissipation. Any hotter than that and they will fail in short order. The main problem we see with the GT 6L6GE tubes is the early failure rate. KT66Chinese Shuguang KT66: These are soft sounding and have a mushy feel when compared to a real Genalex KT66. They are fairly truncated in the low end and although the high frequencies are not brittle like other chinese production tubes they simply seem to lack character and harmonics. Sovtek KT66: These are again not a real beam aligned KT. The low end is better than the chinese KT but it's a trade off because the sovteks have the seemingly patented brittle high end going on so these are a better match for humbuckers, single coils beware!Sovtek Genalex KT66: A better effort by sovtek and not bad all around. Definitely not a copy of the original when it comes to tone. The best way we can think of to describe the tone is polite and a bit plain. They don't have that "bloom" in the upper mids that the original Genalex has.JJ ELECTRONIC KT66: This tube was not meant to be a copy of any prior KT66, it is a unique design based on the extremely successful JJ KT88. It uses the same plate structure and bottle that the JJ KT88 uses but that is where the similarity ends. The JJ KT66's have the big "bloom" in the upper mids that is open, natural and harmonically complex just as the Genalex KT66 has, but the low end is powerful with a deep response without the mush. We have been very happy with these tubes in just about any amp and these are really great is Mesa and Marshall amps. These are a real hand beam aligned KT tube and now have become a real favorite for all of us here.6550After the release of the JJ 6550 we took the time to revisit all the 6550 tubes. We used a 100 watt Anderson Amp to audition them and we ran quads of Sovtek and EH, Winged C, the JJ 6550's and various NOS 6550's including GE's and Amperex Coke Bottle 6550's. Even though we have never really been a fan of 6550's we do like the Amperex better than the RCA's and GE's, so the Amperex has been the standard to beat. Everyone here took time to evaluate all the 6550's at low to moderate volumes and then we went to full on volumes to hear what they had to offer. Each set of tubes were biased at 70% of 35 watts and then 80% to see how the reacted, this is standard procedure around here. The RCA 6550's are a bit softer than the GE's and everyone here was quite surprised that these tubes were nothing to really get excited about. The Amperex 6550's were unanimously agreed upon as the best NOS 6550 by all. Sovtek and EH 6550: These are the same tube and both are boxy Winged C 6550: We actually like this tube better than the chinese and russian KT88's. This had been the best sounding new production 6550 until the release of the JJ 6550. The =C= has a nice balanced tone without getting brittle in the highs, a good offering.JJ ELECTRONIC 6550: We were all wondering what JJ had been able to do with a 6550 design, so before we lit a quad up we went back to our agreed upon benchmark Amperex 6550's for another listen. After a short warm up and bias for the JJ 6550's we were all nodding in approval about the moderate volume clean tones which were warm with a nice sparkle. The balance was very good, no boxy mids and no brittle highs, very nice. Then we cranked the volume and this is the first time I can remember spontaneous laughter breaking out during a tube rolling session. We all looked around at each other, took a step back and realized that the JJ 6550 was NOT your typical 6550! The breakup is raw, crunchy, gritty and just a lot of fun to play. A few minutes later we came to the conclusion that if you could bottle "Angus" these tubes would be it, AC/DC in a bottle. Definitely the most unique and different 6550 to date when driven hard. The JJ 6550's don't make as much power or sound as fat and thick as the JJ KT88 but they definitely fill the void between a 6L6 and a KT88 that is second to none. KT88Chinese Shuguang KT88: These are really the chinese 6550 in a different bottle and we can't recommend them for anything other than target practice or Christmas ornaments... Very bland.Sovtek and EH KT88: These are one in the same and again not a real KT88 and more like a mediocre 6550. They work, they make sound. The low end falls apart pretty quickly so not the greatest choice for Bass amps or for players looking for a big tight chug.Sovtek Genalex KT88: Again these are better than the standard sovtek KT88's but the reason you don't see more written about these is because they are simply nothing special and we personally like the Winged C 6550's better.JJ ELECTRONIC KT88: This tube was first designed back in the early 90's by JJ to be a completely new take on the KT88 design with the ability to withstand peaks of more than 50 watts. These tubes are as musical as a real Genalex with the ability to create the fullest and most exacting image of any tube in its class. Fat, full and a low end extension that is really unbelievable. When overdriven they have a great growl. PRE-AMP TUBES Sovtek 12AX7WA and WB: We lumped these two together because there is very little difference between them. They are both pretty lack luster. The lows are shallow, the mids are sterile and flat and the highs are grainy and harsh. There seems to be no difference in tone from the silver plate WB compared to the gray plate WB. When overdriven they get thin and hairy. Sovtek 12AX7WXT+: A little better than the WA’s and WB’s. Rounder and more linear when clean but brittle. When over driven this tube gets piercing and compresses hard. They also have a nasal like sound. Sovtek 12AX7LPS: An improvement over the WA/WB series sovteks. It has better definition and is more linear than the others when played clean. It has decent detail but it's fairly flat sounding. When over driven it retains quite a bit of it’s definition but still seems to have that sovtek harshness in the upper mids and highs. The break-up is not very smooth. This tube stays clean for a long time and then breaks up very quickly so it’s hard to get to that sweet spot where you can play clean by picking lightly and get distortion by digging in. Sovtek Electro Harmonix 12AX7EH: A slightly different version of the sovtek LPS. The first EH 12AX7's were the exact same plate as the LPS which was 5/8" long. Then because the microphonics were high they changed to a short plate that is 1/2" and this helped to quiet them down some. A little better gain and on average a little better performing tube. These are best suited for high gain amps if you don't mind a fuzzy / buzzy high end distortion. Not a good tube for vintage amps because they lack warmth.Sovtek Tung Sol: Once again the same tube as the newer short plate sovtek EH tube with the exception of the conventional star style mica and the plate coating is a little darker. These are on average a little lower in gain than the sovtek EH but have slightly more warmth. The sovtek tungsol is absolutely nothing like the original Tung-Sol when it comes to tone.Sovtek Mullard: Yet again the same tube as the newer short plate sovtek EH but these are lower in gain and rather odd sounding. I much prefer the sovtek tungsol to these and both are rather harmonically bland.You can see in the first pic that the older sovtek EH is identical to the sovtek LPS. the second pic shows the old EH next to the newer short plate EH which is identical to the sovtek tungsol with the exception of the star mica and slightly darker plate coating.EI 12AX7: Once again the problem here is finding good one’s, but when you do this tube is very linear when played clean with a nice high end, not piercing or grainy. When over driven it looses a bit of low end but still remains rich and full sounding with nice harmonics. The breakup is pretty smooth. Over all this is a very nice tube and comes a lot closer to being what we would call a world class tube. Groove tubes 12AX7: These are mainly the Shuguang chinese tubes and although the later 9th generation tubes are certainly better than the early chinese efforts these are still harmonically bland with a lot of fuzz when distorted. Over the years we have found that lots of players who basically grew up on these tubes (children of the 80's and 90's) quite like them. We do convert a lot of players who find that after they have a number of years under their belt they prefer gain that has good definition without the fuzz. No harm, no foul, as we have said before there is no right or wrong when it comes to tone, use what does it for you. Groove tubes also offers all of the sovtek tubes which are reviewed above. If you contact the GT SAG department (Special Applications Group) and ask for the best they have, 90% of the time they will sell you re-branded JJ ECC83S's at 30.00 a pop!Groove tubes 12AX7M: These are the chinese so called mullard copies. These are dull, very low in gain, short lived and nothing like a real Mullard... Thank you for playing and NO cigar.JJ ELECTRONIC ECC83S: The newer (released in 2002) ECC83S tubes are much improved over the original JJ ECC83 it was obvious that JJ had done their homework. The new "S" tube has an improved mid and high range. It’s even more natural and smoother than the original when played clean and the chime and sparkle are top shelf. When over driven this tube has it! I can honestly say that this tube surpassed my all time favorite Telefunken 12AX7. It’s thick, lush and doesn’t compress as hard as the original. It maintains all of it’s sparkle and definition at all levels of saturation. The best in current production 12AX7 type tubes with the highest current output.JJ ELECTRONIC ECC803S: The ECC803S's are great sounding tubes and have a very thick and fat tone with a little more high end than the ECC83S's. The ECC803's are lower in gain by about 10% than the ECC83S's and because of the extremely long plate in the 803S they are more susceptible to mechanical noise and feeding back at high volumes. This is why we do not recommend them or warranty them in small combo amps but they make a great V1 in most all heads where they provide a very thick and rich tone. The ECC803S's also work well in all positions for Fender Heads such as Bandmaster's and Bassman's providing a very vintage type tone.Both the JJ ECC83S and the ECC803S tubes are available in Gold pin versions. These tubes are built to tighter tolerances and they are very smooth sounding. So if you want a smooth tone they are great but if you like a little grit in your tone like a dirty Keith Richards rhythm tone or an Angus tone then standards are better.JJ ELECTRONIC ECC83MG: This is a “Mid Gain” 12AX7 type tube. It utilizes a medium length ribbed plate design that is much like the old Amperex and Brimar European designs. It retains all of the definition and detail that the ECC83S short plate and the ECC803S long plate tubes have but it has slightly less gain than the ECC83S but a bit more gain than the ECC803S. Sonically it’s nice and thick sounding with a good edge that’s not brittle. It has plenty of definition even when used in an amp with lots of gain and the microphonics are very low. The ECC83MG is a little more polite than the ECC83S which is pretty aggressive. The ECC83MG has a fair amount of harmonic density but remains very open sounding whether played clean or overdriven. All in all it’s a really nice sounding tube.JJ ELECTRONIC 5751: The JJ 5751 has all of the qualities we have come to expect from JJ Electronic, a nice tight low end, a natural open mid, a great harmonic structure and a sweet high end that is not brittle. This is a great tube for V1 if you're trying to drop the gain a little and improve headroom. You can also use a balanced version of this tube as a phase inverter to further increase headroom in amps that incorporate a long tail phase inverter circuit and usually use a 12AX7 or ECC83.