KT66 vs. 6L6 Tubes In A JTM45...How Much Difference?!
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- Опубликовано: 8 июл 2024
- A few weeks ago, I introduced you to my Vajra JTM45 Clone - which I'm absolutely loving! It's based on the original mid-60s design, which was "borrowed" (and slightly adapted) from the Fender Bassman circuit by Jim Marshall. It's a classic rock powerhouse, and a sound we all know.
The previous owner of this amp had it running on 6L6's, but I wanted to restore it to being powered by the original KT66 tubeset....but in the process, shoot some before-and-after footage to see how much of a difference the simple change made. After shooting the 6L6 footage I took the head to my long-time local Bristol amp tech Mike Devine (aka 'Amploft'...he's an electronics genius, so do check him out if you're in the South West! amploft.co.uk) to pop the KT66s in and re-bias the circuit so that they were in their happy place. In the meantime I left the mics on the 2x12 cab, and as soon as the new tubes were installed, I plugged it all back in and played the same things at the same settings with the KT66s.
So...what do you think? Is one more "Marshall" than the other? Or do they make negligible difference? Comment below!
Guitar is a Gibson Les Paul Standard w/ ThroBak SLE-101 PAFs, played through a Vajra JTM45 Clone into a Zilla Studio Pro 2x12 with Fane F70 and Celestion Heritage G12H55 speakers. Recorded with an Aston Spirit Condenser, '70s Sennheiser MD441 and sE RNR1 ribbon mics, with a Schoeps CMC6 room mic.
0:00 Intro
5:24 Clean
7:31 Low Gain
9:26 High Gain
12:38 Maximum Gain
14:36 Outro
joeperkinsmusic
jp@joeperkins.co.uk
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For me the difference was very subtle. A to B comparison I could tell them apart, but it's just the barest shade of difference. Your playing the same parts a week apart was incredibly consistent. You have my admiration!
Aha thanks Robert...I probably need some new riffs! :P
The KT66’s had a ”grunt” I really enjoyed! Very good video! I really like your positive attitude:-)
Thanks Sebastian!
There is only 3 tube manufacturers left in the world. Shuguang in China, Reflector factory in Saratov Russia and JJ in Slovakia. Groove Tubes just relabel tubes along with Tube Amp Doctor, Ruby tubes etc. I like the Shuguang and Gold Lion ( Russian) KT66.
Thanks for all the info Neill :-)
I love kt66s. They just have this round full tone that’s thick and never harsh. Just pleasing to the ears.
Amen - I didn't expect to hear such a big difference.
The 6L6 draws about 0.9A and a KT66 draw about 1.3A, the only tube i could find so far that actually draw pretty much the same is the Tung Sol KT66 tube because the heater current is about the same, also the biasing is pretty much the same. Also there is JTM45 clones with EL34 tubes, in that case you would need a different Output Transformer that has the 6.6kOhm winding for use with KT66 or any other tube like the 6L6. Its a hazzle to read up on all these things before swapping tubes. Modern amps often has like you mentioned in this video a Switchable BIAS for 6L6 and EL34, how ever it does not mean that in all amps that has this its ok to just flick the switch and put in some KT66 in there... its confusing for some people, even for me some times.. you make great videos, Cheers.
True KT66's draw 1.3 amps on the heater voltage, 6L6's only draw .9 amps. thats a 50% difference, they are not a direct replacement. Swapping these could cause damage to the power transformer. The Tung Sol KT66 only draws .9 amps so it's not considered a true KT66, some say it's just a 6L6 with the shape altered to look authentic. would be interesting to hear a different brand of KT66 used in the compairasion.
23%!! no 50%!!!!!!!
@@dominiquemercier408 .9 + 50%= 1.35
Mick Grabham built a JTM45 for me several years back. He used all NOS mustard caps and carbon resistors. Fantastic amp. He used NOS Mullard preamp tubes and I bought a pair of Genelex KT66's for it, got them fairly cheap because the guide pins had been broken, but the seller put tube savers on it, they were NOS. Also bought a NOS Mullard rectifier tube to complete it all. My amp tech friend told me that 6L6's and KT66's were compatible so I swapped in some JJ6L6's. I was shocked that I couldn't hear any difference. Of course I put the KT's back in because it was biased for those, but pretty interesting comparison.
Thanks Dave :-) Yeah, I too was surprised how little was in the KT66 vs 6L6 debate, and that's not even going NOS...good to know others have found the same thing. :-) P.S. Would _love_ to try a set of your PAFs one day - have just demoed the ThroBak PG-102s w/ vintage wire; would be great to see how yours compare! :-)
@@JoePerkinsMusic I'm not currently taking new orders, I have too many old orders am trying to finish off, but my work is really slow to build, since I do all my own machining work and plating and things I dont talk about that are very time consuming. But I do peridiocially offer ready built sets to stay alive and announce them here on RUclips, so subscribe if you want to know. A little HINT---if someone says they are using "vintage wire," MAKE THEM PROVE IT. Some wire being called "vintage" is only 10-15 years old. I know this for a fact. Make them send you photos of the spools. Dishonesty is all too common among the "booteek winders." I ALWAYS show the spools of wire from the 50's that I use, and they are NEVER PLASTIC spools, only aluminum and steel spools were used back then.
Thanks for all the info Dave :-) Fingers crossed I can try out a set of yours one day - the Four Uncles ABR-1 is also on my radar, though your PAFs in a Les Paul is the goal! 👍
Groove Tubes isn't a manufacturer. They're a distributor/rebrander. Their main thing is buying tubes from existing manufacturers at a certain spec and then labeling/relabeling those tubes with the Groove Tubes brand and selling them in matched pairs and quads.
As for these particular pairs of tubes, they _sound_ similar enough that a few degrees on the EQ knobs could probably wipe out most of the tonal differences. I can't say that one set ruled and the other set drooled or anything like that. (Through _these_ headphones, anyway.) That being the case, my preference between these two sets would boil down to _feel._ Did one set take a lighter touch than the other in order to get picking-strength clipping? Was one set louder than the other? Better sustain? Noise or microphony? Durability? Those are some of the factors that would influence my preference.
I think they both felt pretty similar overall - but I _was_ playing them a week apart, so it's not too easy to compare that directly! I'll have to report back on durability...so far the KT66's are sounding phenomenal!
@@JoePerkinsMusic I love it when a plan comes together.
thank you so much for the comparison dude help way more then I spected
I much preferred the 6L6s (especially for cleans) and I did not expect it.
Interesting as always Joe 👍🏽 !
(no valves coming out of China since the fire last year as the factory burnt down - only 3 tube factories left currently Russia, Czech & Slovak Reps many tubes that come from these are just rebranded/tested and sometimes 'designed by the different companies currently selling vacuum tubes - all of this much to my buddy Dave Friedman's chagrin in trying to source good & reliable tube sources) and it maybe of interest to you Joe but on Tone-Talk (YT Channel) tomorrow (Sunday 12 @ 18.00 in UK) we have Johan Segeborn as a guest
Ah thanks for the info - had no idea about the fire…might be why i couldn't find any of the Chinese tubes!! Oh awesome…I love Johan’s channel!! I might not be able to watch it live (I’ll try!) but I’ll definitely check it out in the next couple of days if not. Thanks for the info :-)
I couldn't tell any difference on overdrive, but on cleans I like the 6L6 better, a little brighter and clearer mids. More "alive" sounding.
Thank you for this comparison! When I one day get a JTM45 clone I think I’ll start with KT66.
I didn't have to go through the whole video, but I am going to still, at least to know the differences between the two, The KT66 are warmer, and great sounding, the 6L6 are brighter, and sound almost better when playing single notes, and the Chords sound better played through the Kt66. there's not much difference to tell to pick the two apart, it's a close call though, It is like pick ups, depending on what you are trying to achieve for sound and tone. I prefer the KT66 because of the Original Tone is hard to find, and unequal in tone. Effects are dime a dozen to flow into the amp and out the speakers , so I am enjoying all the different options available. Very Good Video, Thank you. also to add, the 6l6 are distinguished as to being clean and more modern.
Just wanted to add, i was researching the KT66 earlier in the day, as i've been interested in this tube. When i found out the Tung Sol could be subbed without damaging my PT i was giddy. Thanks for this video, i think i'm going to order a set and give them a shot, they do sound just a bit brighter in the upper mid's which is what i'm looking for. I subscribed to your channel and look forward to future vid's.
Thanks Scott - glad it was a useful one!
Both sounded great in your amp. I liked the 6L6 cleans and the KT66 for max distortion.
6l6 are thinner more bottom end. Less overdrive.. Like a fender.
Kt66 fuller more mid less bottom end. More overdrive. Like a marshall.
Nice video.
Thanks
I'll have to agree about the kt66 having subtly more mids/high frequency and less low end, while the 6l6's sounded smoother and warmer. But in all honesty in the context of a live band mix, I don't think anyone could tell. Great video.
Yep - very subtle differences!
Love KT66's - you are the best Joe.
But i must say im not sure if i preferred the 6L6 or KT's
Different, i guess :)
I did a similar experiment with 6L6s, E34Ls, and KT66s in my PRS Archon 50 head a couple years ago. My experience was that they all sounded pretty much the same clean, but the KT66s seemed to put out noticably more/thicker bass on the dirty channel. The Archon is kind of a thick sounding amp to start with, and the bass boost from KT66s was almost too much if I was using my 7-string. I ended up going with E34Ls in the long run.
They're both great tubes. I love the KT66s and they're my favorites. 6L6s are a good substitute. Very similar sounding tubes.
I actually thought the breakup characteristics of the KT66 tubes had more complex harmonics. The 6L6 breakup was a little more... sterile sounding, in my opinion. Nice little shootout.
Thank you for a great comparison!
I have an early JTM45 RI with vintage spec filter caps. I have tried various 6L6s and KT66s. Now it's running Gold Lion KT66s.
I agree that the difference is more prominent when playing clean(ish). At first I had the impression that the EQ was broader with KT66, but maybe it's because there is a better definition/tone separation. The cleans are to die for and the dirty tones are great too.
I should mention that I most often don't jump the channels, but only use the bright channel. Playing Les Paul with PAF clones.
I have the same amp does it need bias after you change the tubes? meaning you need to take it to an expert or I can just change them by myself?
@@arissp4950 Always check/adjust bias when replacing the power tubes. If changing from 5881 or 6L6 to KT66 you also need to check that the power transformer can deliver the higher current for the preheat circuit. If not the power transformer can get damaged.
I'd say the KT66 was a tad brighter, and at full drive levels the 6L6 did seem a bit muddy in the lows (with humbuckers, at least). Overall they were surprisingly VERY similar. In the end, KT66 for me!
Agree!
Kt66 tubes exhibit more bottom end, less throaty mids , more even mids, rounded off highs as well a sense of 3 dimensional.
Mike @ Amploft looks after my amps as well :) was pleasantly surprised to hear his name mentioned
Ah amazing! Mike is a legend :-)
I found this interesting and timely as I am waiting for a fryette power station ps-100, and that has KT66 but the 50 watt model uses 6L6
The tweed bassman amps actually ran on 5881 tubes, and had a 12ay7 in v1 instead of a 12ax7. As you say, Jim swapped those, and shortly after using kt66s (which I prefer over 6L6GCs) he switched again to EL34s.
I have a JTM45 clone running on KT66 power tubes, and my understanding is that I would need to switch out the output transformer if I wanted to run E34L J/J tubes in there instead. I think I'll stick with the KT66s. Cheers!
was going to post just this. My bassman has tung sol 5881s in it
@michaelhager4270 yeah, I also have a pair of NOS USA tung sol 5881 tubes in my 1967 Bassman.
I Love the characteristics of the beam Tetrode/Kinkless tube. I installed them in a Fender twin reverb.(KT66) Its an animal.I an using one G12H and one Tone tubby Alnico. If you notice the amp shines more pushed.Thanks for sharing. c];-)
Really nice comparison. Well done. Very subtle difference between the two. Possibly hidden in a band mix. Was there an aparent "feel" difference when shifting between the two in the room? I found through my experiences that I have favored 5881 and the E34L type EL34 tubes especially when playing at above 30% volume.
Was hard to tell, as I had to shoot the two tube types about an hour apart...I don't think there was anything _too_ noticeable though.
First comparison video I've ever heard a difference. Kept my head down through all the tests and clean no difference, but when the dirt starts coming the 6L6's are definitely warmer.
Now if I could only get mine to drive that hard on pentode mode.
I did manage to get some overdrive without a pedal boosting it, but with my ocd set with level maxed and drive at 0 I can get some really nice tones.
Both sounds good :-)
You rock kind sir!
Am I mistaken or do the 6l6's sound cleaner and have more low end? And they do not sound as good as the kt66's?
KT kinkless tetrode all the way. Nice demo Joe. Enjoy your stuff. Cheers from Canada.
Good demo and big difference I'd say.
Simple - 6L6’s are more open with sparkle, they sound better clean. The KiT66’s more compressed excel with overdrive and distortion.
Super vidéo ! J’ai une petite préférence pour les 6L6, un peu moins sale. Et superbe jeu de guitare !!!
I’ve got two of the “early” JTM45 1989 reissues and I’ve fitted both with GoldLion KT66’s. I’ve run 5881s, EL34s, but settled on the KT66s. For reference, I’m an early AC/DC tone chaser.
I have an early reissue head I purchased new in 1990-ish (it's a long time ago, and I'm old now so - ish!). I specifically wanted 6L6's for that Bassman sound, it has the standard 6L6GC's. I also specifically wanted a big clean sound as I intended it to be a pedal platform and didn't want it to break up too much. I've never gone after that power amp break up with it - my sound is pedal-based for practicality - once an amp is breaking up you've lost the headroom, which you need with pedals or you end up with an increasingly mushy sound that which just doesn't cut through. Mine sounds clearer and more burnished than the one you were using. A literally HUGE sound (perhaps because of the 6L6's being the GC variant?) After years of frustration with master volume type amps, including the JTM45's immediate predecessor - a JCM whatever (honestly, very, VERY average) the JTM45 was suddenly IT! Still is.
The 6L6's imparted a slightly fuller and more rounded tone, sweeter and less harsh highs. The KT66 are similar to, but slightly nicer than I'd expect EL34'S to sound, the difference to the 6L6's more apparent when driving the amp. 6L6's, or better still 6L6GC's, are the nuts, IMO.
hi..which brands did you use for the fi conftonto test.Are they by chance vslbole nos?
6L6 was Groove Tubes; KT66 was Tung-Sol - neither were NOS; both current-production.
please make a video on swapping the first preamp tube or v1 to a vintage mullard i61 and i63, GE12ax7wa, rca 12ax7a/7025 those are the greatest hits. thanks!
Tried them in my old Maglite and they are both hot and pretty dim.
👍 KT's & EL34's.......RULE !!!!!!!!
I much prefer the 6L6 tubes... for me they are tighter and more defined where I found the KT66 tubes a little bit fluffy... almost on the verge of muddy
I have early Marshall clone (ulbrick arena 50) with good lion CRYO kt66 tube pair.
From what I was told about the tungsoul kt-66 are really more like a 6550 sound compared to other kt-66 power tube but still a great sound
They're pretty close. But I think the KT66's sound more "Marshally". Something in the midrange sounds slightly better to my ears.
Agreed - it's a subtle difference, but a few % more Marshally
Joe,... did your amp tech discuss impedances with you before swapping power tubes? KT66 and 6L6 tubes are not technically interchangeable even though you re-biased the amp... KT66's are looking for an Output Transformer with a primary impedance of 8k. 6L6's are looking for roughly 4k. It is extremely important to know the primary impedance of your specific model Output Tranny.... here's the rub,... if your OT has a 4k primary and has secondaries of 4/8/16,... and you put in KT66's it's only okay if you understand that the 'reflected impedance' is no longer 4/8/16 outs.... it will be something very different... if you don't take into account the change in reflected impedance you are at least in danger of smoking your tubes, or worst case... smoking your output transformer... figure out exactly what OT you have and make sure to take into account of what your new reflected secondaries are.... just don't want you to roast that cool new amp of yours !! Many blessings, Mark :-)
The amp was designed to run on KT66's and the previous owner swapped it to 6L6's...so if anything, I think the 6L6's were more likely to mess with the circuitry/components!
I'm torn. I love the low mid domination on the 6L6, and the cutting mids of the KT66. I'd get two and run them in stereo lol. I'm currently practicing with a Pro Junior (EL84, in a bigger cab with a 12" speaker and Surfybear Classic Reverb), and a Fender Custom 68 Pro Reverb (6L6) in fake stereo (old school reverse phase "stereo" from a big box 80s Stereo Memory Man). Sort of getting the best of both worlds between open low mids and screaming high mids.
Didn't tweed bassmans get issued with, or were designed for use with 5881's, not 6L6's? I know, on the other hand, that tweed pros ran on two 6L6's, but I don't think the bassman was designed around the 6L6, at least not initially.
Aesthetically kt66 for the win. I've always loved the 6l6 in my tremoverb. Never used kt66 but would love to.
Right away I got the feeling the kt66 were clearer and sounded like they would be more dynamic. Was that the case to you when you played them? Could have been new vs older tubes though.
Can't say I noticed any huge differences...especially a week apart! The KT's definitely sounded more Marshally though to my ears...though only by a bit!
KT66 valves sounded broader and open as though a door was opened and all the harmonics rushed out. I think the GT valves are graded from 1-10 from dirty to very clean, did you notice. 11 months later, which ones are you using now?
Still using KT66s - I don't think there was _too_ much in it, but to me the KTs sound like more like a JTM45 is 'supposed' to sound. 👍
The JTM45 OT is a bit high impedance for the 6L6GC (8K vs 5k). That suppresses the distortion and highs, but not too bad. They sound looser and less defined than the KT66. Not as good for a classic blues/rock sound.
The KT-66 really jump out of my speakers! I prefer 5881 to 6L6 in most places and the 6L6 sounds good, but the KT sounds MMMMMM. Just what you want. The more I listen the 6al6 sounds like an American amp with celestial speaker. And in a way it's just a bossman through a closed back. KT66 all the way.
Worth noting…, GT DOES NOT manufacturer tubes, they just rebrand them!! Another thing, the output transformer primary needs ALSO to see the correct tube impedance; and they are extremely different between 6L6’s and KT66’s. That’s not only important when matching speaker cabs to the secondary, but tubes as well (primary).
kt66 cut through better. 6v6's a little more big bottom / scooped but also more headroom?
Yeah, I think the KT's were a little grittier than the 6L6's with the levels set the same
Most of an amps overdrive tone comes from the preamp hitting the phase inverter
output tubes make very little difference
You crank the amp at home without an attenuator?
Yep - fortunately my nearest neighbours are quite a way away. :-)
Jimi Hendrix had KT66 in his Superlead 100, I like more the KT88 tone + 6L6 :)
Those subtle differences can probably be tweaked with gain or EQ. I was interested in a pair of KT66 to replace 6L6 but unless they blow I’ll stick with ‘em. Cheers!
You could try some Tung Sol 7581A next tube change. They bias like 6L6GC, but have the tight bass and round high end like a good KT66, and are very robust. BTW, the JJ KT66 don't sound like real KT66.
No EQ can sound like an old KT66.
The new ones are not same
Great demo mate, love how you always keep the tempo the same between changes.. drives me mad when people speed up and bash harder. Lol
I think I got lucky with this one...I'm usually like a broken race car :P
On the clean tone it was indistinguishable, on the low gain the 6L6 sounded smoother, at high gain when you played chords the 6L6 sounded clearer and smoother but when you played single note the KT66 was the winner, max gain the 6L6 was smooth and clearer.
To me, 6L6 were the winner in this comparison. I like the soft eq of 6L6 tubes, the KT66 have that british "grittiness" that is cool but sometimes those "harsh" highs makes my ears uncomfortable.
Preferred the 6L6's, but that's just me.
You should try kt88.
It's the same than kt66 but more.
KT66 obvious winner
Definitely 6l6's! Sweeter to my taste
I thought the 6L6s sounded nicer, the cleans were sweeter and warmer. They had an airiness about them, maybe more headroom? The KT66s had a grittier sound and suited the higher gain stuff better, strong mids, a sizzly top end and tight bass. That dampened chugging style of playing you did was great with the KT66s.
As a fellow lefty, I have to say it still looks weird
I don’t have to be mindful of anything! I’m an American
kT66.. more body, detailed highs and sweet bottom... better than 6L6 in my ears..
No bass at all, and treble and mids also turned so far down? Why?
It's a very thick amp, being a derivative of the Fender Bassman (a bass amp, originally). Most people say JTM45's need to have the bass turned down very low/almost off - and that's definitely the case with this amp.
6l6 for clean, KT66 for overdrive
Sounds like KT66 has more bottom end
I like the 6L6 GC tubes better but it is a close call for sure
Sounds about as good as a peavey bandit transistor amp. The only time it starts to really come alive is when you are driving it for a while and its getting hot with an amp like that ... then its nice, sure. So that is what i pick up. Yes, i've had a bunch of tube amps, fender, marshall ... and played guitar for a living for decades so my ears detect some of it. I also would like like to hear with other guitars.
The only valve that will run at 560 v is the GEC.
Play it with a Stratocaster