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  1. emento

    emento Guest

    Has anyone tried this?

    From http://www.eurotubes.com/euro-n.htm
    KT88's in a Dual Rectifier??

    Yes! KT88's in a DR... This is one way to make a DR into "Frankin Rectifier" The bias on the DR's is set very cool for 6L6's and EL34's but the average KT88 draws about double the natural plate current of the average 6L6 so when you run KT88's in a DR with the amp in the EL34 rectifier mode the bias comes up to where it should be and the bottom end gets VERY deep and strong along with a punch that is truly enormous!

    May the amplifier Gods have mercy on your speakers!!

    I would also like to dispel a couple myths that I've read lately on the Harmony Central forum about KT88's ( yes I do read the forum every once in a while when I have the time ). First off Dual Rec's are capable of using either 6L6's or EL34's and LOTS of you DR players out there are using the JJ E34L's in your amps and have been doing so for years. A standard 6L6 draws .9 amps of heater current where the JJ E34L draws 1.5 amps. A KT88 draws 1.6 amps so as you can see a quad of KT88's will only draw .4 amps more that a quad of E34L's and is not going to cause a problem. Hell I even use a quad of KT88's in my 1982 Evil Twin which means that it's having to deal with a 6.4 amp draw instead of a 3.6 amp draw from a quad of 6L6's and it's been running STRONG for almost four years now. My 5150ex has a total draw of 6.2 amps running two KT88's and two E34L's once again this amp was made for a quad of 6L6's with a total draw of 3.6 amps and yes, it's a MONTSER and gets played very hard and often now for over two years. The bottom line is that most all of the amps out there that can run 6L6's can run E34L's or even KT88's if there is room.

    Now about that pesky bias question. Dual Rec's are a unique amp because of the different settings available with the "spongy" and "bold" settings along "6L6" and "EL34" settings and the "solid state" and "rectifier" modes. Since a KT88 will draw almost twice the natural plate current that an average 6L6 draws your bias will go up! An average E34L will draw only about half the natural plate current that an average 6L6GC draws. When a DR customer calls me and is looking for an improvement in his clean tone and an improvement in dynamics I will often recommend using the JJ 6L6GC's in a cooler grade and running in the "EL34" mode which will get a DR to draw about 32 to 40mA per tube depending on whether it's run is SS, REC, Bold or Spongy. This gets the bias much closer to where it actually belongs when using a cooler grade of 6L6.

    An amp that has anywhere from 450 to 500 plate volts can run a JJ KT88 at between 50mA and 90mA per tube. Here's a quick run down on the bias of moderate grade JJ KT88's in a DR.

    These setting are in the "6L6" mode.

    Rectifier mode in spongy setting = 16mA which is VERY cold so you can imagine how cold a 6L6 would be!

    Rectifier mode in bold setting = 18mA which is still VERY cold.

    Solid State mode in spongy setting = 28mA still cold.

    Solid State mode in bold setting = 32mA still a little cool.


    --------------------------------------------------------------------------------

    These setting are in the "EL34" mode.

    Rectifier mode in spongy setting = 44mA which is actually just getting out of crossover distortion and sounds very good.

    Rectifier mode in bold setting = 50mA nice an aggressive with great dynamics.

    Solid State mode in spongy setting = 78mA now this is getting some heat in the tubes and the dynamics are spectacular.

    Solid State mode in bold setting = 88mA this is getting up to about 80% of max dissipation and will shorten the tube life about 10 to 15% and the tone will start to "brown" but it's a lovely sound!
     
  2. gbisn1960

    gbisn1960 Member

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    hold the phone!

    im using e34l's in my hot cat right now.. are you saying that if i can use that tube.. i could also use the kt88??? kt88's in a hot cat??? hmmmmm ill have to do smore research on this.. ive been thinking about putting kt66's in my germino masonette.. dont know if i would want the headroom of the 88 :)
    let me know if yall think im crazy!
    Jon
     
  3. KLB

    KLB Member

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    If you mean KT88 in the Masonette, you probably don't want to do that because the Output Tranny likely won't handle the high idle current and/or full-output load. (Better check with Greg) At any rate, the OT is too small to give more headroom with any other tube than the 6V6. Also, the Masonette OT has a primary impedence of 9K, which is high even for a 6V6. The KT88 will put out more watts into a lower impedence, closer to 5K or thereabouts. The typical KT88 OT is much, much larger than what is in the Masonette.

    One more point: KT88 are physically large, and may be too close together for good ventilation, or won't even fit.
     
  4. gbisn1960

    gbisn1960 Member

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    ah.. i was just going by some numbers.. thought maybe it would work.. oh well.. btw.. i was talking about the hot cat :)
    Jon
     
  5. KLB

    KLB Member

    Messages:
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    Does the Hot Cat have adjustable bias, or is it cathode biased?

    If you try the KT-88 in the Hot Cat, please let us know what it sounds like. Also, with KT88 you might want to experiment with setting the impedence to half the actual speaker load.
     
  6. gbisn1960

    gbisn1960 Member

    Messages:
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    Location:
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    its cathode.. there is no biasing.. just to refresh on what i saw and maybe it would work.. maybe it wouldnt.. you said that the current draw on a 6L6 was .9 and the E34L draws right at 1.5.. i have those tubes in my cat right now and if its drawing 1.5 shouldnt i be able to run something thats at 1.6 or would that be horrible on the amp??? those numbers just got me thinking.. i know kt88's in a dual rec actually opens up the amp a little more making it more airy.. i have a friend who has tried them in 3 of his dual recs.. a tremoverb, a mid 90's dual rec and an early rec... he said they sounded the best in the early one.. but he said it does a number on all of them! worth a shot.. anyways.. get back with me on those numbers.. and on the hot cat.. the only speaker loads i have is 4 and 8.. the speakers in the combo at set at 4 ohms.. so i cant go any lower :( .. but i can try it out with my germino 2x12 cab.. that may be pretty cool!
    Jon
     

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