My first foray into the KT88 world

Discussion in 'Tube Audio' started by mroboto, Jul 6, 2018.

  1. mroboto

    mroboto Super Member

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    Already owning two Chinese tube amps, 300B SET and EL84 PP, really appreciating them, I decided to go for another Chinese amp, a KT88 SE amp.

    I just ordered this KT88 6N8P 5Z3P assembled amp.

    Hard to find a thread about this amp as it is not branded , unbranded.

    KT88-6N8P-5Z3P.jpg KT88-6N8P-5Z3P Back.jpg

    Not sure if it will roll in my main system with my modified Paradigm 7SE , or if it will be part of the bedroom system with 90's JBL LX600.

    I already have a bunch of 6SN7 and 5U4GB tubes , the only new tube (for me) is the KT88.

    I think the stock tubes are basic Shuguang.

    I do not have the highest expectations, but I think that this amp have good potential.

    Waiting fot it to arrive in the next weeks.
     
    Last edited: Jul 6, 2018

     

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  2. Tubeglowpio

    Tubeglowpio Active Member

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    I'll be interested to hear what you think, there are many types that look to be made by the same people, I almost bought an el34 one because it was on sale for about 200 bucks only. I felt that it wouldnt last long so moved on.
     
  3. mroboto

    mroboto Super Member

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    One thing I will miss with this amp is an input selector switch and inputs jacks for at least 1 or 2 more components, thinking about adding this.
     
  4. primosounds

    primosounds SE KT120 w/ 6J5G drivers. LCLC ps + 2 x 5ar4 Subscriber

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    If you are really serious about sound quality you should just get a preamp so you can take the different front end designs out of the equation. In other words if you keep on getting an integrated amp the front end of each unit will have its own sonic signature. So all your listening impressions will be in part determined by the quality of the parts in front of the amp section.
     
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  5. mroboto

    mroboto Super Member

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    I try to keep the signal path short, the only other tube in the pre section is the 6DJ8 in my TubeDAC-11.

    Sometimes, to have a shorter signal path, I use my SA9227 + PCM5102A USB DAC (Note:This DAC needs capacitors added on the regulators to function properly), and is modified with Wima MKS2 10uf 50V output coupling caps.
     
  6. mroboto

    mroboto Super Member

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    The first thing I think to do is to add a Thermistor to AC input, a 120 ohms 1.8A 240V rated NTC 120D15

    I don't know if it is safe to also add the same to the 350V PT secondary ?

    There are 680V rated thermistors, but they seems to be low resistance.

    I want to have a really soft start for HV too.
     

     

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  7. sKiZo

    sKiZo Hates received: 8641 Subscriber

    Looks to be a pretty basic amp, and probably based on a tried and true design. Have fun with it!

    For more IO, the Little Bear MC1022 will give you two for one for about $20 ...

    One question on the speaker jacks ... are those set up for multiple ohms or multiple speakers out? I don't see a switch, so I expect it's 4-8-16ohms out ... nice option that.

    PS ... is that a choke hiding behind the PT?
     
  8. mroboto

    mroboto Super Member

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    A selector switch box option keep the amp original with is straight signal path , it's a good option.

    The speakers jacks seems to be placed in 8-4-0 - 0-4-8 configuration, I think.

    This is a 5H 250mA choke.
     
    Last edited: Jul 6, 2018
  9. Tubeglowpio

    Tubeglowpio Active Member

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    putting a thermistor on the primary should give some sort of soft start to everything on the secondary.
     
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  10. mroboto

    mroboto Super Member

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    Yes, I understand, but to give an higher soft-start coeficient to the HV than what I give to the heaters..

    I believe that soft start have a big influence on tubes life expectancy.

    I did this to my EL84PP , with a 47 ohms 3A to primary and 120 ohms 1.8A to the 280V secondary, and the amp works very fine , I can even use a WY3GT Weber Copper cap solid state rectifier and know the start up is relatively soft.

    280V on my EL84PP amp was not a big step from the 240V thermistor rating, but 350V ??

    I think to put them directly to the pin 4 & 6 (inputs) of the 5U4GB rectifier, as the wire from the secondary must lead directly to there.

    Due to the relatively low current demand compared to the 1.8A thermistor rating, and the already soft-start primary I hope this will be fine if I do so.
     
    Last edited: Jul 7, 2018
  11. primosounds

    primosounds SE KT120 w/ 6J5G drivers. LCLC ps + 2 x 5ar4 Subscriber

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    Check the specs on the part you are interested in. The companies like Digikey and Mousser always have the entire specs from the manufacturer. Sometimes you can find the specs online from the manufacturer as well.
     

     

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  12. mroboto

    mroboto Super Member

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    The datasheets are not explicit , I remember reading somewhere that they are rated for 240V , maybe this is mainly because this is the highest main voltage in the world, or because they are rated for Max. 1.8 or 2.0A @ 240V for exemple.
     
    Last edited: Jul 6, 2018
  13. Tubeglowpio

    Tubeglowpio Active Member

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    If you really worry about the high voltage inrush current then just use a 555 timer ic with a relay to delay the b+ switching, that along with the thermistor will work great.
     
  14. mroboto

    mroboto Super Member

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    I want to teep it as simple as possible, but thanks for the suggestion.
     
  15. Tubeglowpio

    Tubeglowpio Active Member

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    Then how about a separate toggle switch to switch the b+ in?
     
  16. mroboto

    mroboto Super Member

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    I don't want to forget the B+ offline and cause cathode poisoning to the tubes.
     

     

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  17. Tubeglowpio

    Tubeglowpio Active Member

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    That could take hours to happen, not sure what else to suggest. Just try the thermistor then, it wont hurt anything and I do believe the ratings for voltage could be higher with smaller current.
     
  18. primosounds

    primosounds SE KT120 w/ 6J5G drivers. LCLC ps + 2 x 5ar4 Subscriber

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    That is probably AC volts.
     
  19. mroboto

    mroboto Super Member

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    Yes, for AC, I didn't find rating for DC use, but it must be very lower if there is any.
     
  20. corbin

    corbin Active Member

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    Really curious about how these Chinese tube amps stack up - I've only read positive things from people who have them. My experience is fairly limited with only vintage solid state "mid-fi" (though the Sony is better than anything I've heard) and I'm seriously considering trying one of these.
     

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