Kegger/blueglow kt88 project

Discussion in 'Tube Audio' started by Tubeglowpio, Jan 6, 2019.

  1. Squidward

    Squidward Scrappy Mod Staff Member Moderator

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    4,709
    Location:
    Bikini Bottom (Ann Arbor, MI)
    Wow, really nice build.

    I've never used JB Weld, I didn't know you could just do that with a piece of aluminum. Pretty neat.

    Only thing that concerned me was the electrolytic bypass caps on the cathode resistors. I assume that because they're chassis mount and high-wattage they don't get very hot?
     

     

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  2. tubetime

    tubetime New Member

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    Lansing, MI
    Thanks! The caps are not touching the resistors. They are at least 1/4" away. The resistors are 15 watts and dissipate a little over 3 watts apiece but still get hot. The heat rises into the chassis and caps remain cool. Chassis is deep at 3" could not have wired like this with 2" chassis. I should have taken a pic at an angle to show lead dress height differences on all.
     
  3. Tubeglowpio

    Tubeglowpio Active Member

    Messages:
    387
    Location:
    AZ
    Cant wait to be enjoying that amp too! Great work, so did Kegger's final schematic differ from blueglows? Kegger's knowledge is missed, I was so busy lately that I didn't get back on here really till a week or so ago and noticed Jay had passed, that was a bummer to see, I hope he went peacefully. All contributions of knowledge will live on through AK.
     
  4. Tubeglowpio

    Tubeglowpio Active Member

    Messages:
    387
    Location:
    AZ
    I get to worried about that stuff so always try to keep caps away from any heat sources, are those nichicon muse caps? I usually go with Elna silmics II but that's because I got in the habit of using them for solid state amps in the past.
     
  5. Ruidoso Bill

    Ruidoso Bill AK Subscriber Subscriber

    Messages:
    112
    Location:
    Ruidoso, New Mexico
    What a nice job on assembly, I am hoping mine will look that great. Any Particular reason to have not made it switchable? I am awaiting Edcor delivery and Parts connexion was out of a couple parts, the waiting is not easy for me. By any chance did you create a drawing of the top chassis layout with measurements? Good idea about the aluminum to support the top, Mark didn't mention flex other than mentioning the transformers weight, chassis seems pretty stout. Looks to gibe more isolation between the power supply and the audio wiring. Only change I am making from the Blueglow layout is adding some terminal strips prior to the input and output jacks, should make it easier if they ever need replacement.
     
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  6. invaderzim

    invaderzim AK Subscriber Subscriber

    Messages:
    897
    Location:
    California
    That build looks like artwork. The underside of mine looks like someone dropped a bowl of spaghetti.

    Switching to the ECC85/6AQ8 preamp tube was one of the best 'upgrades' I've done to mine.
     
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  7. Tubeglowpio

    Tubeglowpio Active Member

    Messages:
    387
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    I don't like the aluminum chassis for bigger iron like this, I will be using the steel chassis.
     
  8. Tubeglowpio

    Tubeglowpio Active Member

    Messages:
    387
    Location:
    AZ
    The first amp I built was a copy of a Magnavox 8601, I used more terminal strips than needed so I could easily switch out and try different components, that thing was a mess, was pretty quiet surprisingly though.
     
  9. invaderzim

    invaderzim AK Subscriber Subscriber

    Messages:
    897
    Location:
    California
    I've thought about trying to clean mine up but I don't get any hum so I figure I shouldn't mess with it. I have done some minor tidying up and learned the hard way to only make one change at a time in case something gets worse.
     
    Last edited: Jan 11, 2019
  10. Tubeglowpio

    Tubeglowpio Active Member

    Messages:
    387
    Location:
    AZ
    At one point I had my Maggie 8601 sounding really nice with a tube phono and pioneer hpm 60 speakers, it was so 3d and involving with a hauntingly real midrange and really sweet top end sparkle. You would swear Bob Dylan was in the room with his guitar and harmonica, I had rolled just the right tubes finally and it was so close to perfect for me but then I tried to change it to fit a different pair of speakers and to sound better using a phone to drive it and work better in a larger room and it was just never as good as it was for those few months that I had it almost perfect. Once I'm done with some other project I really am thinking of messing with it again then draw up a schematic and build it on another chassis. I'm going to build the dgse version first to see if maybe that's at all similar to what I was searching for. I'm still enjoying the Rh-84 I built, it's pretty darn smooth hifi sounding but I would say the modified Maggie in that setup was more appealing in a certain way.
     
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  11. invaderzim

    invaderzim AK Subscriber Subscriber

    Messages:
    897
    Location:
    California
    There are few things worse than losing the magic sound and not being able to get it back.

    I went through it with this amp a few times as I tried to chase down some imaginary audio nirvana. I thought it was amazing when I first built it and then started with the "well if it is this good now then how much better will it be with this capacitor or that connector or this other thing changed.
     
    Last edited: Jan 11, 2019
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  12. primosounds

    primosounds Powered with pure tube sounds. Subscriber

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    3,070
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    The phenomenon you refer to is like love at first sight. Where the initial impression is so good that it becomes a strong link in your psyche and so stands out from the rest of the listening sessions. It is very hard to avoid unless you are extremely familiar with the rest of your equipment and make you first listening sessions with the same reference music. After the initial glow has worn off critical listening will reveal certain traits that are positives and also the negatives.
     
  13. Tubeglowpio

    Tubeglowpio Active Member

    Messages:
    387
    Location:
    AZ
    That could be part of it and true more in certain situations but I have to say that I always have my wife double check no matter if its a good or bad change and she too described it the same basically saying it sounded warm and welcoming and sounded really nice to her ears, I'm sure if I would have had the equipment I have now I would have seen some differences in maybe distortion or even something with freq response, who knows. I will say it was a romantic affair with that amp, almost felt like I was cheating because I chose to listen to the amp over being with her a couple of times haha.
     
  14. Tubeglowpio

    Tubeglowpio Active Member

    Messages:
    387
    Location:
    AZ
    Was this the Kegger kt88 Amp? So basically are you saying this one is basically perfect per the schematic? I know that project was running for awhile and a lot of tweaks were made along the way.
     
  15. invaderzim

    invaderzim AK Subscriber Subscriber

    Messages:
    897
    Location:
    California
    I started with the Alex Gendrano version and I have to say that the changes I've implemented from the Kegger schematic have actually made improvements. My initial changes that went downhill were more of capacitor 'upgrades' or tweaking the tube bias hotter type 'improvements' and voltage changes and similar. They were all done without a scope and too many at a time to be able to easily tell which did what. It was a case of a little bit of knowledge is a dangerous thing
    It went from initially where if there were quiet spots and then just a voice in a song I'd jump a bit thinking someone was in the room to after the changes piled up not listening to it much. So then I went in and redid it as close to original as possible with new terminal strips to replace ones that had been soldered and resoldered. Now I've been slowing doing things like the LED Bias and grid stopper resistors and grid leak resistors etc. Making actual changes that have been tested over and over rather than 'this capacitor is supposed to sound amazing' changes that then end up with less than perfect solder joints in awkward to get at places and lower quality sound. I still have a few changes to get to for it to be a complete match to the Kegger schematic but I have the parts and will do them one at a time.
     
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  16. Tubeglowpio

    Tubeglowpio Active Member

    Messages:
    387
    Location:
    AZ
    I hear you, Instead of building it exactly like kegger/blueglow schematic I am jumping straight to the kt-120's and will be running just a little more voltage and about 30 mA more of current per output, I changed the power supply to a dual choke filter as well and changed those cap values but I used the power supply design software to show their should be an improvement in both ripple and transient response so I think it's worth a try and I think as far as biasing too hot I think the key when moving up to the kt-120 is keeping around the same plate dissipation percentage as the kt-88.
     

     

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  17. jdsalinger

    jdsalinger AK Subscriber Subscriber

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    @invaderzim, what caps did you use that were "original" ? Just curious.
    Your comment about jumping sure did bring back memories of mine. Yes, that amp can get spooky sometimes.
     
  18. invaderzim

    invaderzim AK Subscriber Subscriber

    Messages:
    897
    Location:
    California
    I started with Auricap then went to Russian k40 and then some huge Russian Teflon ones and finally some Mundorf silver gold oil ones (I think). On the cathode bypass capacitors I went through F&T, Nichicon, Elna and even a black gate of some sort. I thought I could tell difference with some but I now question my ability to judge the sound fairly after a recent instance where I swapped out my cheap DAC for, what for me is, an expensive one and was initially blown away by the improvement in sound only to then put in a switchbox so I could quickly A/B them and ended up in a blind test nearly half the time picking the cheap DAC as the best sounding one.

    I also must have changed out the bias resistors a half dozen times as well as power supply capacitors and 2 different rectifier tubes and a handful of different resistors in the power supply section. With nearly a dozen different 6N1P tubes and 6550, 6L6GC, EL34, KT77, KT66 and KT88 tubes I was the poster child for chasing useless tweaks and I think only now am I getting close to the original sound again.

    Oh, yeah, and at one point I even managed to bias a set of tubes hot enough that I exceeded my power transformer rating and killed it (I assume that is what did it in).

    I think a key difference is those changes are well thought out and serve a purpose.
    I'd read a post from someone talking about how something made a big improvement in their amp and I'd just have to try it.
     
    Last edited: Jan 12, 2019
  19. Ruidoso Bill

    Ruidoso Bill AK Subscriber Subscriber

    Messages:
    112
    Location:
    Ruidoso, New Mexico
    I am just curious with this size of chassis 17 X 10 why wouldn't a steel partition between the PS section and the audio section be adequate, even my old Dynaco equipment always had such a partition, I have already ordered a bottom cover which I intend to cut and make a partition, maybe moving Mark's BlueGlow design over more to the PS side would be enough isolation. Just a thought.
     
  20. Tubeglowpio

    Tubeglowpio Active Member

    Messages:
    387
    Location:
    AZ
    I think that would help an aluminum chassis, it's not a bad idea anyways to block some emi.
     

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