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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: 27 Apr 2011, 20:10 
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Location: Chilliwack, BC
Wow! What a gorgeous amp :thumbsup:

Cheers!

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PostPosted: 28 Apr 2011, 09:55 
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Joined: 05 Nov 2010, 21:07
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Location: South East US - Tennessee
Seriously nice!

I continue to be amazed by some of the DIY projects that show up here. Some of you people just have too much fun! ;) :thumbsup:

Is that actually sandstone?

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PostPosted: 28 Apr 2011, 11:52 
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Location: Arizona, USA
Hi Dean, Lovely build. :thumbsup: Yes you can do pp-parallel. I would go for well matched tubes to optimize the performance. The power loss you noted is expected. A fair rule of thumb for class A amps is that if the pentode version will do say 10 watts RMS, the U/L version will do about 2/3 that and the triode in the 1/3 to 1/2 range. I have tried parallel outputs and was not as happy with them as with the single tube versions. A little more power (remember that twice the power is not twice the loudness) may not make that much difference. The parallel variations seemed to loose a little of the magic. To parallel the tubes I would change the series grid resistors to about 2.2K and bump up the overall idle current to around 140ma to 150ma. You could go to double, but since tube matching (or mismatching if you choose) is never perfect you want a fudge factor in case one tube in a pair hogs more than its fair share of current and frys. The existing output transformers should be fine as the design is fairly insensitive to that. You may find it beneficial to reconnect the NFB with the PP-parallel tubes. Please let us know what you do and how well it works so we can pass it along to others.

Related, I tried a 6V6GTB (Ruby tubes) version of the Poddwatt and while it sounded fine the output was less than the EL84s by about 25%. Cute, really retro, but ....... A 6L6 version makes a lot more sense for Retro look and sound. Run the 6L6s at about 120ma a pair up to B+ of about 350. Load Z of 8K is fine.

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PostPosted: 28 Apr 2011, 15:43 
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Joined: 18 Jul 2010, 15:48
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Thank's everybody.

This material is Corian (product by Du Pont)

On web side http://www.triodefestival.com/rubrikeakt.php?pageNum_rec=1&totalRows_rec=14&list=43&published=1, You can see how I worked with this material.
Of course, there You can see many DIY amp and speakers, who made with many love and skills.
Dean


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PostPosted: 30 Apr 2011, 05:09 
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Location: Australia
Yes great looking amp. I know Decware use EL84s in SE for 2W. I thought 3W of my 6AS7 set was low. 2?

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PostPosted: 27 May 2011, 21:00 
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Location: Arizona, USA
Hi Everyone, I retired at the beginning of the month and have been traveling a bit. ;) One trip was to the Lone Star Audio Fest. The Poddwatt was a hit there. I walked it around to several other exhibits that had sensitive speakers (90 db/w and up) and it drew praises every time. It beat out the SETs every time. Two of the exhibitors want to use it in place of the amps they brought this year. Both amps were name brand good designs. For 5 watt per channel amps this one is hard to beat. It even drove the Martin Logan Prefaces (not ESLs) that I brought quite well. My thoughts are that as good as SETs are (many are really good), a clean class A push-pull U/L design will have less distortion and more power (often translates into better control of the speakers). I don't want to start a SET vs PP battle :angel: , I just report what happened. If you are already reading this thread, I probably am telling you things that you agree with.

Good listening
Bruce

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PostPosted: 28 May 2011, 07:10 
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Location: Australia
Bruce: I know you're a big fan of this tube. You have always said it is the best sounding tube you have heard. Good to hear they liked it at the show.

Instead of the 5751 will a 12AX7 drop straight in and sound as good?

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PostPosted: 28 May 2011, 07:53 
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It is said that 5751 are superior to the 12AX7/ECC83.The 12AX7/ECC83 have way to high gain to be really good for audio.

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PostPosted: 28 May 2011, 08:07 
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Soundbrigade wrote:
It is said that 5751 are superior to the 12AX7/ECC83.The 12AX7/ECC83 have way to high gain to be really good for audio.

Yes I see where Bruce has tried them and prefers the 5751. What about the 6N1P?

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PostPosted: 28 May 2011, 08:31 
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A different tube with different characteristics, closer to 6922 or ECC85.

I wonder if a 12AU7 could be working if diagrmas are reasonable redesigned.

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