5881 Out-Kt66 In- What to Expect?

Discussion in 'Amps and Cabs' started by DonW, Jan 26, 2006.

  1. DonW

    DonW Velocity Town Angel Silver Supporting Member

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    I plan on a tube change for my 50 watt head. 4 -12ax7's and 2 5881's w/ a master volume. I intend to buy some NOS Mullard or Telefunken etc. 12ax7's and KT66. I'm shooting for a sort of raw grind that I've heard on other KT66 loaded amps. Are the KT 66's different enough for me to notice a change in tone? The 5881's have a nice mid/bottom and so do the KT66 amps I've heard. Thanks!
     
  2. Driver

    Driver Member

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    i've found it to 'open up' the sound and make it clearer - not as boxy and compressed as before. almost like it widened the frequency response of the amp. this was switching from sovtek 5881wxt+ to groove tubes kt-66hp on a peavey butcher (jcm800 clone). so, by no means am i an authority on this. i just chose the groove tubes because they were cheap and readily available to see if i like the direction of the change. and i do, so i'm probably going to be looking for nos kt-66's also.

    however, had terrible experience with their "matched" quad, so i ended up buying another pair in addition to the quad. so it ended up costing me $180! ...for GROOVE TUBES!!! i would highly recommend that you stay away from them.
     
  3. Matt H

    Matt H Guest

    hit up the valve arts kt66's (or the shuguang- whatever particular labelling of the chinese kt66)... they're great tubes... i was especially impressed with their nice round bottom end...
     
  4. amper

    amper Member

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    I agree with Driver. It definitely makes everything sound a bit more open.

    I'm a big fan of Groove Tubes KT66HP's. I have four pairs (one #5, two #6, one #9), and one quad of #5's. All of these tubes were picked out of clearance bins at local GC's. I don't think I've paid more than $25/pair. The quad I got the other night cost me $45.

    Right now, my narrow chassis F-50 1x12 combo has

    V1 & V2 = Ampeg/Electro-Harmonix 12AU7's
    V3 & V4 = Mesa/Boogie 12AX7's
    V5 & V6 = Groove Tubes #5 KT66HP's

    ...and the speaker has been changed from the original Mesa/Celestion Black Shadow 90 to a Mesa/Celestion Vintage 30. I'm very happy with the way my amp sounds.

    The 12AU7's will probably come out, and I'll put back in the Mesa SPAX7's I had in there. I like the 12AU7's, but they don't sound any better than the SPAX7's, just less gain and a little darker. I'll try the 12AU7's in my V-1 Bottle Rocket next.

    On top of the KT66HP's, I also have a whole bunch of other GT power tubes for my Univalve. I've never had a problem with GT.
     
  5. DonW

    DonW Velocity Town Angel Silver Supporting Member

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    Thanks for all the replies. I'll post my results when I get the switch done.
     
  6. Driver

    Driver Member

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    amper - about your groove tubes KT-66HP's, have you gotten different bottle sizes? that's why i'm so pissed at them. all they have to do is match them, and sure enough, when the "matched quad" arrived, there were 3 bottles of one size, and one bottle about 1/4" shorter! now, i understand that they still might match, performance-wise, so i popped them in my fixed bias amp, and to no one's surprise, the smaller one was glowing red hot! so i got another "matched pair", and again, one big bottle, one small bottle. this time they both turned on red hot. yes, i switched around the positions of the tubes, and the problem is the tubes. i'm glad things have worked out for you with them, but in the end, i spent $120 on the quad, and another $60 of the pair, and i still don't have 4 tubes that glow the same. me personally, i'm not buying GT again.
     
  7. Jimetti

    Jimetti Member

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    Your amp is "fixed bias"?

    It's not the tubes...it's you!

    Did you check and adjust your bias with the new tubes?

    Fixed Bias means you must re-bias when you change tubes. Cathode bias means there is no need to re-bias when changing tubes.

    Take the amp and the tubes to an "amp tech" and have the new tubes installed and biased.
     
  8. Matt H

    Matt H Guest


    soooooo not true.

    bias is bias- you either adjust it when you put in new tubes, or don't... but saying that a cathode biased amp doesn't need to be rebiased when changing tubes but a fixed bias does? that's completely wrong.
     
  9. bluesforstevie

    bluesforstevie Member

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    Real KT66 aren't a drop in replacement for 6L6 based platforms. They draw about 40% more heater current. I'd check with your amp manufacture and make sure your tranny can handle the extra current draw.
     
  10. Driver

    Driver Member

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    i'm totally confused now. either way, shouldn't they either all look like they are going to explode, or none of them? if they were properly matched, there wouldn't be 1 of the 4 acting differently, right?

    about the biasing, i thought you can't bias a peavey unless you do the "bias mod". and when i switched the order of the tubes, the same one looked bad. so 1 of the 4 tubes burns differently in a "matched quad". that's my fault?
     
  11. Matt H

    Matt H Guest

    it sounds like you've got a poorly matched set... OR- one of the tubes is just not up to snuff!!! they may have been matched at a less stressful operating point (lower voltages... namely lower screen voltage)

    as for biasing- yes, ANY amp CAN be biased!!! it's the way the damn thing works!!!

    the "bias mod" (note: i know nothing about your PARTICULAR amp) likely just involves replacing a resistor of fixed value with a pot of some sort (which is nothing more than a resistor of variable value).

    hoenstly, there's no difference between having a "nonadjustable fixed bias amp" and a "nonadjustable cathode biased amp"- theoretically, both should be biased, or at the very least CHECKED when new tubes are installed. In these situation, if you need to adjust the bias of the amp, this is accomplished by either changing the resistor value as needed (continuing to leave it a nonadjustable bias, be it cathode or fixed)

    OR installing some type of pot (or rheostat in the case of a cathode biased amp) thus making it adjustable.


    but all of this "cathode biased amps don't need to be biased but fixed bias amps do!" crap is just wrong... in all cases, the bias should be checked- and if it's wrong, should be adjusted. the method of bias doesn't automatically adjust itself perfectly... (though, i guess it could be done, but it'd involve a lot of solid state components!)
     
  12. Driver

    Driver Member

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    solid state components, you say? i wouldn't put it past them - it IS a peavey after all. it makes a lot of sense about the biasing. i pretty much figured that that was the case (replacing the resistor with a pot of some sort).

    but my point is, in all of this off-topic banter, is that GT does a poor job matching the tubes they package. supposedly, they actually manufacture this particular tube, but in most cases all they do is match tubes. and if that's all they do, they do a crappy job at it, and i'm not giving them my money anymore. and i was only mentioning this (my experience and money spent) as a warning to the original poster. so, whatever. back on topic?

    by the way, yeah, i'll take my amp to a tech and have him re-bias it, and also find out if it really is my fault that one tube burns hotter than the others. thanks guys.
     

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