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Thread: 6L6's vs KT66's

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    The Drama Dude CTN's Avatar
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    Default 6L6's vs KT66's

    a couple of questions.

    1: are these interchangeable tubes, sorta like EL34s and KT77s?

    2: what are the major tonal differences between these two tube types?

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    Stratoblaster Tone Meister STRATDELUXER97's Avatar
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    Default Re: 6L6's vs KT66's

    Quote Originally Posted by ConvoysToNothingness View Post
    a couple of questions.

    1: are these interchangeable tubes, sorta like EL34s and KT77s?

    2: what are the major tonal differences between these two tube types?



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    Guitaris Maximus Stratman's Avatar
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    Default Re: 6L6's vs KT66's

    Not interchangable!

    GEC KT-66 (The real ones) take 1.3 amps for the heater circuit and are kinkless design!

    6L6 tubes only draw 0.9 amps for the heater circuit.

    If your transformer can handle that heater amp load, then go ahead and install the KT-66 tubes and re-bias.

    If not, DON'T risk blowing up your transformer and amp....
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    Default Re: 6L6's vs KT66's

    The KT66 is just huge sounding in all frequency ranges with lot's of harmonic detail, but not necessarilly that upper mid swirl of an American 6L6. When I use KT66's in Marshalls, I notice a distinct overdrive tone best heard on the early Cream albums. Listen to a lot of 60's EC, that's what they sound like. In shared cathode Marshalls the KT66 has way more bass than a regular 6L6, but it's not really a tight bass. I mean its almost over powering, but thick bass. For deep, tight, punchy, bass, the 6CA7 is the one for that.

    Some KT66s pull 1.5 amps heater current, so don't use these in most non-Marshalls.

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    Default Re: 6L6's vs KT66's

    JTM-45 with KT66's are a thick creamy milkshake.


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    Default Re: 6L6's vs KT66's

    Quote Originally Posted by Stratman View Post
    Not interchangable!

    GEC KT-66 (The real ones) take 1.3 amps for the heater circuit and are kinkless design!

    6L6 tubes only draw 0.9 amps for the heater circuit.

    If your transformer can handle that heater amp load, then go ahead and install the KT-66 tubes and re-bias.

    If not, DON'T risk blowing up your transformer and amp....
    This is a fact.

    What is the amp in question??
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    Default Re: 6L6's vs KT66's

    Quote Originally Posted by Scott_F View Post
    JTM-45 with KT66's are a thick creamy milkshake.
    It's funny...everybody seems to equate the tone of a JTM-45 with KT-66's...I've heard and used JTM-45 clones with KT66's, EL34's, 6L6's...even 6V6's and they all have that signature JTM-45 thickness as well as the chime on top!
    If you just read a post by The Guy Who Invented Fire please understand that opinions change, mind sets change and as players our ears mature...not to mention our needs grow and change. With that in mind, today I may or may not agree with the post you just read!

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    Default Re: 6L6's vs KT66's

    Quote Originally Posted by the guy who invented fire View Post
    It's funny...everybody seems to equate the tone of a JTM-45 with KT-66's...I've heard and used JTM-45 clones with KT66's, EL34's, 6L6's...even 6V6's and they all have that signature JTM-45 thickness as well as the chime on top!
    The other tubes are close to my ears, but the super thick and unyeilding ultra low end bass is lacking in anything that isn't a real KT-66 tube IMHO. I can tell a difference between the Tung Sol KT-66 and my Groove Tube KT-66 tubes. The Tung Sol KT-66 is pretty much a standard 6L6 in a big bottle. Nothing comes close to the Groove Tube KT-66's that came standard in the Edana. I have yet to successfully try the Shuguang KT-66 tubes (I bought a set that lost vacuum the second I fired them up). I have heard those Chinese KT-66's have some serious bass response as well though.

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    Default Re: 6L6's vs KT66's

    Who would need more bass than what's available in a 6L6???

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    Default Re: 6L6's vs KT66's

    I'm not saying that I "need" it. I'm just saying that I can tell a difference and I prefer to have more thick bass rather than less.

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    Default Re: 6L6's vs KT66's

    I swapped the 6L6's in my Peavey Vypyr with Tung-Sol KT66's. It was a direct swap. Didn't have to re-bias or anything. I noticed a better bass response, but all around they just sound better to me. I can't describe it. It's a more full sound. However, the bottles for the KT66's are bigger, so depending on your amp it may be hard to fit them in if your tube sockets are close together. Also, if you have "bearclaw" retainers, you will have to remove them because the KT66's have a metal base. Hope that helps.

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    Tone Member BenPerkins's Avatar
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    Default Re: 6L6's vs KT66's

    Is there a list of small bottle KT-66's?


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    Default Re: 6L6's vs KT66's

    small bottle and lower current draw suggests that the tube isnt a kt66 and probably wont sound like you want it to. sucks the golden lions dont fit

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    Tone Member BenPerkins's Avatar
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    Default Re: 6L6's vs KT66's

    There's a seller on eBay that has KT-66's that are 3 inches - so I might give that a shot


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    Default Re: 6L6's vs KT66's

    Quote Originally Posted by BenPerkins View Post
    Is there a list of small bottle KT-66's?


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    The JJs and the Tung Sol are supposed to be 6550 /KT88 sized, which is smaller than the Gold Lions or the Chinese version. The Tung Sol KT-66 has the same current draw as a 6L6 (0.9 amps).

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    Default Re: 6L6's vs KT66's

    what brand? as i alluded to before it might not be an actual kt66, could be a 5881 or 6l6gc they are calling a kt66 since no one keeps track of these things anymore. a 5751 used to be a 5751, now people sell soft 12ax7's labeled as 5751 but they are just soft 12ax7s.

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    Default Re: 6L6's vs KT66's

    fwiw my jtm runs on el34s. It works good on 6l6s too.
    Thick and bassy as heck.
    I think it is more about the amp design than the tube choice.
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    Mojo's Minions Lake Placid Blues's Avatar
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    Default Re: 6L6's vs KT66's

    ^^ I also often run my JTM45 with EL34s. There's a pretty dramatic difference as to where the bias pot needs to be adjusted to, but both tube types can be adjusted for within the pot's range. The amp is brighter and cleaner with KT-66s (gold lions) than with EL34s, which are darker and more easily over driven. To get the impedance matched better, you can run the amp into an 8 ohm cab with it set for 16 ohms when using EL34s, depending on which output transformer the amp has. A big factor for the tone of a JTM45 is actually the rectifier tube. One would not think it would effect the tone, but it does. You can completely change the tone and feel of a JTM45 by changing the rectifier tube.

    As to running KT-66s in a cathode biased amp: I have been trying several big bottle octal tube types in the new mini Jubilee. (one of the amp's designers posted on the marshall forum that this is perfectly okay with this amp.)

    KT66s: classic rock and heavy blues heaven. More clean head room than with EL34s and brighter. Glassier cleans, and more broken crunch when over driven. Probably not for metal at all.

    6L6GCs: Very open and clear across the board. More clean headroom but rather boring distortions and over drives, in my opinion. Might be good for pedals.

    6CA7s: Close to EL34 tone but everything thing is bigger and bolder, especially the bass. Less snarl in the upper mids compared to regular EL34s. Crystal clear highs even on high gain.

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