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  #1  
Old 12-01-2008, 02:25 PM
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Nirky Nirky is offline
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Good schematic for SE EL34/KT88 amp

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!,
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Old 12-01-2008, 04:32 PM
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I've built this one this past Summer http://diyaudioprojects.com/Schemati...-Amplifier.htm
It's very simple to build, nice sounding, but it is tube rectified.
Glenn
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Old 12-01-2008, 04:37 PM
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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. 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.
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Old 12-01-2008, 04:57 PM
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Quote:
Originally Posted by vfr800fiman View Post
I've built this one this past Summer http://diyaudioprojects.com/Schemati...-Amplifier.htm
It's very simple to build, nice sounding, but it is tube rectified.
Glenn
That is on my list to do. I was going to use 6550 tubes and SS power supply. DO you mind sharing photos of your build?

Cheers
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  #5  
Old 12-01-2008, 07:06 PM
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Pictures are on my page here:
http://webpages.charter.net/porkchop...8_SET_amp.html
The speakers I use with this amp are here:
http://webpages.charter.net/porkchop.../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.
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Old 12-01-2008, 10:08 PM
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Oh hi porkchop. I've seen your BD Pipes before. Great job on the KT88, it looks great.

Cheers,
Gio
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  #7  
Old 12-01-2008, 10:17 PM
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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...
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  #8  
Old 12-01-2008, 10:21 PM
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Quote:
Originally Posted by vfr800fiman View Post
Pictures are on my page here:
http://webpages.charter.net/porkchop...8_SET_amp.html
The speakers I use with this amp are here:
http://webpages.charter.net/porkchop.../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.
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...

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!
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  #9  
Old 12-02-2008, 07:30 AM
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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
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  #10  
Old 12-02-2008, 10:59 AM
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I like the RH84 and RH807 variants. I'm sure that the 807 could be modded for EL34 or KT88.

http://www.tubeaudio.8m.com/RH84/rh84.html

http://www.tubeaudio.8m.com/807/807.html

Good luck!
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  #11  
Old 12-02-2008, 02:42 PM
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Quote:
Originally Posted by Nirky View Post
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...
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.
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  #12  
Old 12-02-2008, 05:09 PM
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Kegger Kegger is offline
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This is what I'd build, and plan on building.

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 Images
File Type: gif KT88_EL34_SE_UL_400V_M1_adj.GIF (14.4 KB, 567 views)
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  #13  
Old 12-02-2008, 05:14 PM
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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).
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