Good schematic for SE EL34/KT88 amp

Discussion in 'Tube Audio' started by Nirky, Dec 1, 2008.

  1. Nirky

    Nirky Active Member

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    I'm getting ambitious and want a winter project for after Christmas. I already have the acrylic plexiglass for the custom chassis and have begun assembly, and now I'm looking for a good schematic for a single-ended EL34 or KT88 stereo amp.

    For simplicity & aesthetics I prefer diode rectification in the power supply. Any types of driver input tubes are fine.

    Anyone know a good online resource? Anyone have a good one, or built one?

    edit: title should have said EL34 doh, OH IT DOES NOW, COOL!,
     
  2. vfr800fiman

    vfr800fiman AK Subscriber Subscriber

  3. jaymanaa

    jaymanaa AK Subscriber Subscriber

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    I've still got the schematics from my SET EL34 amp Tim, and I even have the Heyboer number for the custom wound outputs and choke.:yes: It's a little unique in the fact that the OPT primary Z is 10k (about twice what most folks would run), to keep distortion at a very minimum. You sacrifice some power doing that, but no feedback is necessary, so it makes around 6 watts. It uses 6SL7 drivers with the sections paralleled. It would be an outstanding candidate for SS rectification due to the high B+ requirements (a tad over 500v). Lemme know if you want me to dig them up for ya.
     
    RUmad likes this.
  4. gmilitano

    gmilitano diyAudioProjects.com

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  5. vfr800fiman

    vfr800fiman AK Subscriber Subscriber

    Pictures are on my page here:
    http://webpages.charter.net/porkchop/tubeamp/KT88_SET_amp.html
    The speakers I use with this amp are here:
    http://webpages.charter.net/porkchop/speakers/speakers.html
    I'd be glad to answer any questions you may have.
    I've got this amp set up with a switch for Ultralinear/Pentode/Triode mode. I also have a switch for changing the bias resistor value depending on which tubes I'm running. I've run the standard KT88's, EL34, 6CA7, 6L6G, & KT66's.
    I think my favorite is still the KT88's in UL, which is what the amp was designed for.
    You can find more build details at the diyaudio.com site under tubes, just search for Mikael Abdellah's KT88 SE amp.
    I built a dual mono version rather than two monoblocks. It's more cost effective than buying two sets of power supply components.
     
  6. gmilitano

    gmilitano diyAudioProjects.com

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    Oh hi porkchop. I've seen your BD Pipes before. Great job on the KT88, it looks great.

    Cheers,
    Gio
     
  7. Nirky

    Nirky Active Member

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    Glenn, I've seen that circuit on their website, that's the one that got me interested in KT88. Circuit board is great to make build time quicker, everything goes where it should, but I wanted to move tubes around in the chassis, plus no tube rectifier. Glad you like your amp, is the reason you like UL better than triode mode due to increased power output? How do the EL34's compare to the KT88's?

    Jay, I'd love to get that schematic. I'll pm you with my email in case you don't have it. I confess I don't remember seeing any pics of it on the forum...how do you like it, and is it your main amp now? Hey there is a HK250 on that auction site right now... :)
     
  8. Redboy

    Redboy a few good watts Subscriber

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    I've looked at that schematic before, too. The versatility of it is what appeals to me most. Might have to think about it again... :scratch2:

    How'd you cut the big holes for the oil caps? Or did you punch them somehow? You did a nice job on the chassis!
     
  9. vfr800fiman

    vfr800fiman AK Subscriber Subscriber

    Nirky-
    I just like the sound a little better in UL than Triode, again this is all just personal taste. I will say that this amp isn't very good for rock. I'm a big Zep fan and that type of music just doesn't have the impact it does on high power amp. This amp IS very good for acoustic and vocals, Days of the new's orange album really sounds excellent on this system!
    I will say that with rock on this amp my choice would be EL34's in Pentode mode. I know, more distortion but I think the extra power probably has something to do with it. The EL34's sound "tighter" than the KT88's. The 6CA7's from EH are also very nice sounding in Pentode mode.
    Those BD pipes are using Tang Bang drivers that are 90db efficient, so that also helps. I haven't hooked this amp up to my Altec A-7's yet. Their still in the basement as they have a low WAF. They should really sound good as they are around 102db efficient if I remember correctly.

    Redboy-
    Thanks, the chassis did come out rather nicely. I used a hole saw to do the capacitor holes. The caps are slid into the holes from the bottom and secured from the bottom with screws that are tapped into the chassis plate.
    I like using the turret board approach for all the components. It looks less messy to me, and I'm used of doing it on all my home brew guitar amps.

    Glenn
     
  10. Squidward

    Squidward Scrappy Mod Moderator

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  11. jaymanaa

    jaymanaa AK Subscriber Subscriber

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    Next to my new 2A3 it's my favorite amp, and I reckon it's just the tube that makes me lean toward the 2A3. I'll dig those up and scan them for ya.
     
  12. Kegger

    Kegger Anything can be S "MODed" Super Mod Subscriber

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    This is what I'd build, and plan on building more of.

    I've built this with other tubes and it works quite well, ;)

    You could run 6L6GC's in here as well, (Triode, UL switch)
    Also sub in different drivers like 5965, E180CC, 6829, ECT.
    .
     

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  13. jaymanaa

    jaymanaa AK Subscriber Subscriber

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    I'd like to switch my little bottlehead pre to 12AT7 from 12AU7. The TX is so tiny I'm scared to even try the old 12BH7 trick. I really prefer the sound of the AT versus the AU (not sure why).
     
  14. RUmad

    RUmad Active Member

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    Hey Kegger. Sorry, I keep digging up all these old threads. Do you hear any difference, running those bypass caps around the PSU electrolytics? I've got an amp of a similar design, used all giant motor run caps and solen, but always wanted to bypass them and see if I could hear it.

    Alan
     
  15. Kegger

    Kegger Anything can be S "MODed" Super Mod Subscriber

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    Bypass caps around the PSU electrolytic's yes I've found improvement in the overall smoothness of the amp.

    As to bypassing motor runs and solen's, while I still feel it's good to bypass those with an small film cap, the noticeable differences are much smaller.
     
  16. RUmad

    RUmad Active Member

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    Great. I guess I could give it a try on an amp with 'lytics first, and thanks for the response.
     
  17. RUmad

    RUmad Active Member

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    And what about the difference between triode and ultralinear? What's your opinion on that? I haven't even touched my amp in almost ten years, since I built it, because it sounds amazing to me. Was under there a couple days ago swapping out the Auricaps for Jantzen Superior Z caps. I totally forgot that when I ordered the tranny's I got the UL tap.
     
  18. Kegger

    Kegger Anything can be S "MODed" Super Mod Subscriber

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    UL is generally a flatter, cleaner and wider frequency presentation then triode. (some may prefer it some may not, which is fine and personal preference) :music:

    Me personally I feel single ended ultra linear with a bit of the added local feedback is a fantastic circuit and may be my favorite amplifier design an performance.
     
    Last edited: Jun 28, 2016
  19. RUmad

    RUmad Active Member

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    I truly love the way mine sounds in triode. No treble or bass adjustments, no nothin. Simple circuit, low parts count so I can afford to use some pretty good quality components. I was considering adding a dpdt switch for the UL tap but I think I will yank the unit. I'll directly solder on the screen taps, and IF I like it, I'll add the switch. I can't see how this could sound much better than it does. One of the most satisfying projects I've ever done. Appreciate the input as always!
    Some have said I may like the way rock sounds in UL and jazz in triode. Rock sounds good to me in triode, but I will give it a try.
     
  20. AlTinkster92

    AlTinkster92 AK Subscriber Subscriber

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    Hi Kegger, are you referring to a little NFB in U/L? thanks Al
     

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