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 NEW  Matt presents bias and operation data for the 6V6 tube in SE operation - 6V6 Single-Ended (SE) Ultra Linear (UL) Bias Optimization.

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PostPosted: 10 Apr 2010, 16:18 
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Joined: 14 Feb 2010, 13:13
Posts: 716
Location: Lisbon, Portugal
Hi!

I´ve been reading this nice forum for some time and have found some interesting projects.

I just built a 5751/EL34 stereo amplifier from Bruce´s OddBlocks tube amp for the Group "A" tubes.

It really sounds wonderful, and each time I listen to it, I get impressed.

Although, I was looking for some more ouput power.

I changed some impressions, with some forum mates and got advised from the EL34 limits.

This is a PP output stage with 2 tubes.

I wonder what are the possibilities to re-design it, with 4xEL34 per line? This would be nice, as my audio output transformers can handle 40W continuous. So the 4 EL34 tubes could run very smooth in order to get only 10W per tube?

Any ideas / opinions or even schematics are welcome!

The target is to run 8 EL34 tubes as a stereo amplifier with 5751 drivers.


A very special thanks to Bruce and Ben!


Regards from Lisbon, Portugal!

Miguel


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PostPosted: 10 Apr 2010, 19:11 
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Joined: 06 Apr 2009, 10:08
Posts: 1740
Location: US Pacific Northwest
Miguel;

This is an interesting idea. But I don't think you need to run in class AB bias. Two EL34s alone will easily give you 40W (your output transformer limit) so if you want to run parallel EL34s on each side of the push-pull stage, I would recommend that you bias the stage for pure class A push-pull operation. This way there is far less power supply sag at higher power, no crossover distortion, and very clean operation. This would yield a very clean and responsive output stage.

To keep the tubes in class A operation just chose a bias point the same way you would for a parallel tube SE stage and then limit the drive to one half of this voltage. You may have to play with it a little bit to get the right zero signal plate dissipation, just make sure you don't overheat the plates. In class A push-pull the bias doesn't have much impact on output power so just play with the load line until you get the output power for which your looking without overloading your power supply.

Let us know how it goes.

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It's all about the Glass!
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PostPosted: 10 Apr 2010, 22:46 
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Joined: 28 Oct 2009, 02:34
Posts: 501
Location: Utrecht Nederland
Hi Miguel,

I am very proud of you! Well, you can run tubes in parallel, I will send you the schematic on how to do this in your e-mail, really no rocket science, I did that with the help from Bruce., implying 4 Russian GU32. Didn't you see the picture?


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Greetings from Holland, Ben

My DIY Audio Projects:
- Single-Ended 12B4A tube amp with ECC802S driver
- DIY Push-Pull KT88 tube amp (OddWatt amp from scratch)
- 832 / GU32 tube push-pull amplifier project


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PostPosted: 11 Apr 2010, 09:08 
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Joined: 02 Mar 2009, 12:41
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Location: Vänersborg, Sweden
Remember that the OddWatts are pure classA amps which means you are far from the power figures given in the tube datasheets. For EL34 you will get 15-17W in classA (pushpull).
If you want to use this topology (SIPP), you have to look for heavier tubes like KT88 or EL156, else you are obliged to run the tubes in classAB.

Oh, yes, parallelling tubes will of course increase the OP power, but you also have to change the transformers.

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Magnus

“If you don't know where you are going, any road will get you there.”
―Lewis Carroll


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PostPosted: 11 Apr 2010, 11:01 
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Joined: 14 Feb 2010, 13:13
Posts: 716
Location: Lisbon, Portugal
Hi!

Thanks so much for the replies!

I like the EL34 tubes very much, though I´m looking for some more power.

I´m afraid to upgrade to KT88, regarding sound quality against the EL34´s.

Here are some pictures from my unfinished project.

I´m still working on the PSU cabinet...


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PostPosted: 11 Apr 2010, 12:51 
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Location: Utrecht Nederland
Hallo,

well KT88 do sound good. IMHO

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Greetings from Holland, Ben

My DIY Audio Projects:
- Single-Ended 12B4A tube amp with ECC802S driver
- DIY Push-Pull KT88 tube amp (OddWatt amp from scratch)
- 832 / GU32 tube push-pull amplifier project


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PostPosted: 11 Apr 2010, 19:19 
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Joined: 14 Feb 2010, 13:13
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Location: Lisbon, Portugal
I´ve been reading lots of reviews / comparisions between EL34 and KT88 tubes.

From I saw, it´s quite a different experience.

I got the idea that the main difference bewteen them is that KT88´s have a wider / flat frequency response and so more bass.

The EL34´s don´t have such a rich bottom end (though I´m very happy with them), but mid-ranges / vocals are superb (when I overdrive my amplifier, the first distortion I get is on the vocals, not on bass as I´m used to get).

I´m very tempted to get some JJ KT88 tubes!

They are a direct fit on this project, but I would like to hear some opinions first.

I guess it´s just not right to say that the KT88´s will outperform the EL34´s. They just sound different, and I´m only looking for a power upgrade.

So getting another EL34´s Quad to run them in parallel, is still a high probability!


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PostPosted: 12 Apr 2010, 14:43 
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Joined: 15 Mar 2010, 08:32
Posts: 487
Location: Canada
HT Performance wrote:
I´m only looking for a power upgrade.

HI.

Why you want so much power? What make & model loudspeakers driven by yr EL34 amp? For home use or for P.A. type large place?

Power is not the only thing to consider!

c-J

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"If the facts don't fit the theory, change the facts" quoted Albert Einstein.


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PostPosted: 12 Apr 2010, 15:57 
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Joined: 14 Feb 2010, 13:13
Posts: 716
Location: Lisbon, Portugal
Hi Jack!

These are my speakers: http://www.kef.com/resources/current%20 ... ies_en.pdf

KEF CRESTA C1

Maybe my output transformers are not the best.

The amplifier only satisfies me with the volume potentiometer at about 2 o´clock...

The speakers are not the best, but they have a very nice sound, and so the amplifier! :)

The complete system is running on the living room, which is average size for a flat...

You know, when I decided to start building a tube amplifier I was only looking for best quality, indeed I do have it!

The previous and still gorgeous amplifier Sony TA-FA3ES is still here, and it really plays so much lowder, but now, I like the tube amplifier´s sound much more!

Also my Sony MDS-JA30ES Minidisc which has fulfilled my ears, sounds so aweful conected to the tubes!

Oh dear... What to do?


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PostPosted: 13 Apr 2010, 01:39 
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Joined: 08 Aug 2009, 03:11
Posts: 2229
Location: Chilliwack, BC
EL34 in UL or pentode will peak power at 38 or 39mA of AB1 bias with a B+ of 430 to 480V and load of 4300R.
(I reserached this in my ST-70 ;) )

Cheers!

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-= Gregg =-
* Ratings are for transistors - tubes have guidelines*
Home: GeeK ZonE
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