Good schematic for SE EL34/KT88 amp

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

  1. Nirky

    Nirky Active Member

    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

    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.
  4. gmilitano


  5. vfr800fiman

    vfr800fiman AK Subscriber Subscriber

    Pictures are on my page here:
    The speakers I use with this amp are here:
    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 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


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

  7. Nirky

    Nirky Active Member

    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 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

    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

    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.

    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.

  10. Squidward

    Squidward Scrappy Mod Moderator

  11. jaymanaa

    jaymanaa AK Subscriber Subscriber

    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

    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.

    Attached Files:

  13. jaymanaa

    jaymanaa AK Subscriber Subscriber

    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).

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