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KT66 change to KT88 any point?

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  • #1

    KT66 change to KT88 any point?

    I am going to retube a point to point power amp that currently uses 4 KT66 valves (2+2 stereo) - is there any point in changing to KT88s, for instance improved headroom, higher volume? is it only a question of setting the bias or are there other issues?
    Any info would be great.
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  • #2
    Re: KT66 change to KT88 any point?

    as much as i know the KT88 is not compatible to the KT66. I thought KT88 was like EL34 and KT66 like 6L6 and you have to set more then the bias. But not sure about it.
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    • #3
      Re: KT66 change to KT88 any point?

      you can use either. it's hard to find a good comparison as most companies sell one or the other. I use 66's in my fender and love em, and while i have toyed with the idea of using 88s I have concerns about heat and overdoing the tranny. i would probably just go for a "harder" set of 66's if I needed more headroom (which i certainly don't).
      Fender Twin w/ Weber Speakers, keeley ts-9, RMC2 wah, EB MusicMan Axis Sport w/ p-90's, Heritage Les Paul (HC150) Custom Order w/ AIIpro/Custom shop bridge, various accoustics

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      • #4
        Re: KT66 change to KT88 any point?

        Sorry for a semi-hijack, but .....do you have to rebias if you change from EL34s to KT-88s or are they interchangeable?


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        • #5
          Re: KT66 change to KT88 any point?

          im sure you need to rebias. you need to rebias any time you change tubes, even changing from one 6L6 to another.
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          • #6
            Re: KT66 change to KT88 any point?

            You should rebias whenever you change powertubes...and thats just changing between either old to new tubes or interchangable types (eg. 6550's to KT88's).

            As far as i know EL34's can be changed to 6L6's and vice versa...with some rebiasing of course. But you dont wanna do anything like that if you dont know exactly whats going on in the amp because i dont think its ever that simple.

            And just about Marcels comment above, KT88's are not like EL34's to my knowledge...as far as i know EL34's are kinda in the same region as 6L6's, and similarly with KT88's and 6550's. For example - my ENGL Savage 120 had two 6550's when i bought it and i changed them for two KT88's with just a rebias, but i asked my tech if i could put EL34's in it and he said that it would be lots of hassle and lots of stuff would have to be changed electronically so the amp could take them and it wouldnt be worth it. And also there is an ENGL SE head which can take either EL34 or 6L6 power tubes and it has its own bias switch so that you can interchange the two types and just switch the switch over to either EL34 or 6L6 mode and away you go.

            Hope that helped.
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            • #7
              Re: KT66 change to KT88 any point?

              So if I understand the info correctly, you can go between 6L6s and EL34s with a rebias OR you can go between 6550s and KT88s with a rebias, but if you wish to change over between the two groups, then you need to muck about with the power supply charecteristics (souds expensive!).
              With reference to the tubes I've got at the moment, perhaps a change to a harder (?) tube and a rebias will get me more headroom plus 4 new 12AU7s to keep the noise down. Thanks to all you people for the info, is firsta classe!
              Oh, yeah, while I'm on, it would appear that for GT tubes and TAD tubes (in Germany for us Yorupeens), they both have fixed characteristics for the premium ranges that means that you don't need a rebias when you try tubes of different headroom in the same performance range (PC number?). I suppose ideally you should always rebias, but the expression used is "plug and play" - sounds great if it's true.

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              • #8
                Re: KT66 change to KT88 any point?

                the kt66 is a british version of the 6l6 so only a rebias is necessary to switch between those.
                same for kt88 and 6550, just a rebias.
                but i believe that the 6l6 family, 6550 family, and el34 family all have a slightly different pin configuration so it would be more that a rebias to switch to a different type of tube. there are lots of us made marshalls that came with 6550's or 5881's that were switched over to el34 so its fairly common to do, just a little more involved than a rebias

                oh and going from kt66 to kt88 will give you more clean headroom and more bottom end with a different tone curve.

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                • #9
                  Re: KT66 change to KT88 any point?

                  This amp has ultra high perfomance trannys made by a company called Savage of Devizes that I really don't want to screw up by messing with the pins (they also weigh a million tons, so I don't want to take 'em out either), I think I'll play safe and stay with the original tubes - odd thing though, one side has a GZ34 rectifier and the other a GZ32????? Perhaps it's not so original after all - does anyone know what the differences are and if it's important?

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