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Old 13th May 2011, 04:53 AM   #1
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Default Tube SE power amp , which one??

Hello

As a last project I would like to build a SE tube amplifier.
I built several Solid S. amplifiers over the last 20 years.. So I would like to finish all my project and enjoy listening music.
I need some advise which amplifier to choose between the two project.
The KT88 has PC board lay out, I can make the PC board, I have only one question can I drive with a half ECC83 these amplifier
These project from a Germany website..The owner of the amp wrote he more than happy with the result!
KT88SE Roehrenverstaerker, von Michael Dieckmann
Also I think I can use here 6550 and other tubes??
The another project from a Japanese Website
These is a Super triode mode also half 12AX7 driver stage and 6L6GC power tube.
Also I don't know if the power tube can be replaced by EL34 or KT88 with out any modification on the circuit to get more power.
I would like to get 7 to 10W power but most important the quality of those watts..
Any advise welcome.
I just star collecting the parts . When I have to choose the irons I want to buy something good quality like these..
2 SE Tube Output Transformers 300B 6L6 EL34 KT88 6550A on eBay.ca (item 370354427846 end time 17-May-11 16:03:48 EDT)
It is $400 + shipping import tax etc..
So I have to know which one I choose . Once I purchase the Irons I have to stick with that design..
The 6L6GC use 5K primary
The KT88 use 2.5K primary
Any pro and contra from tube experts welcome!!
Thank you very much
Greetings gabor
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File Type: gif fig157zq.gif (7.8 KB, 1165 views)
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Last edited by gaborbela; 13th May 2011 at 05:06 AM.
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Old 13th May 2011, 05:13 AM   #2
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If you want quality of watts 6L6 clones are not the right choice. For 7 to 10 watt of output pair I would prefer something like 4 of 6P15P in parallel, in triode mode.
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Old 13th May 2011, 06:12 AM   #3
singa is offline singa  Singapore
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Hi, If you are going to spend serious money on iron, might as well get
Tango U808 or SE20 don't know if I got the last one right .Both with multiple
taps then you would not be restricted by choice of tubes.
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Old 13th May 2011, 12:05 PM   #4
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Quote:
Originally Posted by Wavebourn View Post
If you want quality of watts 6L6 clones are not the right choice. For 7 to 10 watt of output pair I would prefer something like 4 of 6P15P in parallel, in triode mode.
I'm with him.
Triode mode is the real deal.
6p15p are cheap.
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Old 13th May 2011, 12:23 PM   #5
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Hello

Thank you for the replies and advise!
Only problem with 4 parallel tube they have to be matched I think.
I do not own tube tester.
My speaker is 90db probably 7W is enough. What about the KT88??
Or if I use 6550 instead KT88 tubes..
Thank one more time
Greetings
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Old 13th May 2011, 12:50 PM   #6
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I forget to me very important to have a working schematic to build something!
With out schematic I'm lost in a tube world..
Greetings gabor
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Old 13th May 2011, 02:44 PM   #7
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Like the 6L6 and all of its higher Pa-max clones, the EL84 weren't designed for triode SE use either. The best triode curves has IMHO the KT66. But today people even use line-output-switching tubes as linear amplifiers (as people use IRF530 switching MOSFETS) or transmitting tubes etc. Paralleling tubes will add distortion, too just because of different dynamical parameters of each valve.
I don't want to discuss about "sound", but you can certainly build a excellent sounding KT88 SE amp for example.
Getting 10W out of in SE is as pentode is easy, as triode it isn't that easy.
You just have to know what you want. Why not EL34 SE. they're very cheap, reliable and everywhere available.
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Old 13th May 2011, 06:07 PM   #8
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Hello
From EL34 I can get max. 5-7W..
I had a Revox mono block amplifier with EL34 PP and ECC83 driver. The sounded awful.
OK these was a old design from 60s..
Also I had a DIY PP EL34 , I do not want to comment.
Many EL34 tube sound cheap.
Like Tesla, Tungsram,EI so on. A pair Siemens or RFT not cheap either $$$..
Yes you right I want to use one power tube to avoid distortion and other complication .
I only can build if I have schematic..I don't know about PP, I'm still open for both..
Even to PP the power tubes good to be matched.
What about the KT88 I posted??
Greetings

Last edited by gaborbela; 13th May 2011 at 06:09 PM.
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Old 13th May 2011, 06:18 PM   #9
tomchr is offline tomchr  United States
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Quote:
Originally Posted by the_manta View Post
Getting 10W out of in SE is as pentode is easy, as triode it isn't that easy.
Depends. I get 13 W out of my JJ 300B's using something akin to George/tubelab's PowerDrive. 400 V on the anode of the 300B, 90~95 mA quiescent current, 5 kOhm primary impedance on the OPT. Yes. 95 mA, 400 V is hot but within the original WE spec. With current production tubes, I have no issues.

~Tom
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Old 13th May 2011, 06:57 PM   #10
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Hi,
The actual sound of a Tube amplifier is very complex thing. I can tell you one thing for sure: In a strong feedback pentode amplifier, the output Pentode does very little to the sound. It's mostly the preamp/driver and the OPT (because of its phase shift and bandwith in the feedback loop) which affect what is called sound. When I swap in my EL38 between EL34, 6L6 etc. The difference is hardly noticable and mostly cause of wrong bias. Or can you hear the difference between a Toshiba and Motorola MOSFET ? (Of course connected as Drainfollower). With less feedback and Triode connected the difference will become significant. Moreover I don't understand the argument with the EL34 brand. I have lots of european EL34, most of them in linear power supplies. My Altec 1568a's play great with JJ EL34. They're cheap and come in matched pairs. About 35$ for a pair, when you pay more, you got duped It's unimportant whether it is labeled JJ, Siemens, SED, RFT or herpyderpy.

The KT88 amplifier from german site has a few flaws. The main problem is, that driving a KT88 to full output and using a good amount of feedback, requires lots of signal amplitude, thus gain from the driver. A single small signal triode is on its limit with this purpose. Especially in this circuit, where the ECC83 has no cathode bypass capacitor which means current-feedback and reduced gain in the driver stage I would rather suggest this amplifier: KT 88 SE-Amp, von Franz Wichlas. The cascode stage gives plenty of gain. But the Power stage is IMHO driven by too low voltage. I would give a KT88 at least 350-400V to gain max. output power.

At first you need to know what you want, How much Power, SE or PP, triode or Pentode. As tomchr pointed out, for triode SE you will need big tubes to get some power.
Regards, simon
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