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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: 23 Aug 2013, 22:44 
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Joined: 06 Jun 2008, 18:23
Posts: 4833
Location: Australia
Thank God tube tube gear doesn't have to test well, just sounds good. Over the last couple of issues of Stereophile there has been some excellent explanations why tubes sound good and how they compare with SS gear. As one reviewer described it is how tube amps sound and how they play are two different things.

How they sound (or how tube amps are perceived to sound): flabby bass, rich warm mids and rounded off highs.
How they play: music flows from note to note, the passion and intent of the music is perfect conveyed, magic happens.

I have taken some poetic licence with the above.

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Projects: "Sanctum" - 12AU7 and 6AS7 direct coupled headphone amp | "retro-Oatley 6J6" - 6J6 push-pull headphone amp with OPTs | "Mimic Carbon" - carbon resistors and PIO caps. MM phono preamp
Website: retro-thermionic


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PostPosted: 09 Sep 2013, 16:01 
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Joined: 09 Jun 2013, 10:10
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Location: Stockholm
At first I didn't hear a difference I stated above, but having had time to acquaint myself with the sound from the Mini Blocks without cathode bypass capacitors I almost was chocked what a great sound improvement resoldering those capacitors made. Most obvious the bass became more tight and realistic but it didn't stop there. Everything appears improved, more transparency and more liquid and highly enjoyable sonics. Now the sound quality of these Mini Blocks clearly surpass my old solid state class A amplifier tough it is very good sounding too. The capacitor shunting the cathode bias resistor thus seems very critical at lowering compression and distortion introduced by the cathode bias resistor, and the Elna Silmic caps to my ears do a very good job in restoring the original signal. I tend to get a little over excited when I think I hear a sound improvement but now I have listened two evenings to the shunt capacitor in the circuit and my very positive impression remains, so I think there is substance to it. Of course, unsoldering those caps was an experimental departure from the design, so only now when they are back in place I can enjoy its full potential as it was meant to be. By the way, the JJ EL84 valves are really nice. but I couldn't resist buying some NOS Soviet 6P14P-EV Reflectors from the seventies that are now on their way, so we'll see what they can do.

Ingvar


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PostPosted: 09 Sep 2013, 22:09 
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Joined: 04 Jun 2008, 20:59
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Location: Arizona, USA
Hi Ingvar, The nice thing about diy is that you can make changes to suit your tastes. In doing so you often learn something new. I have it happen all the time. Things I took for granted but messed with anyhow gave me insights to new ideas on how they worked and often hints on how to make them better. The cathode bypass capacitors don't full bypass the resistors and the arrangement with the smaller resistor on the ground side means that the feed back is slightly greater when the capacitor is in place. The effect on the sound is fairly small (as the amount of the NFB is small), but it can have a noticeable effect. The clean tight bass is one of the design aspects. I always design for flat response down to about 10HZ and usually it goes a bit lower. This does mean larger trannies, coupling capacitors and beefy power supplies, but I believe the results are well worth the effort. I might hate hum and noise....but I love the stuff below 30HZ.

Good listening
Bruce

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PostPosted: 23 Mar 2014, 17:23 
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Joined: 23 Mar 2014, 17:14
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Hi,
Been reading for some time and decided to take the plunge on this one. Seems compact and excellent project. Great contribution from you Bruce.
I did few tube guitar amps (which seem easier :) ), so some experience is already there.
Looking through the schematic and the build pics I cannot get, though, the grounding on the power supply board. Where do the electrolytics are grounded? I don't see a wire going to the center of the board. Sure, I am missing something...
Many thanks in advance
Niki


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PostPosted: 13 Apr 2014, 22:54 
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Location: Arizona, USA
Hi, I've been getting ready for an Audio Fest in Dallas two weeks from now and packing up some of my gear. I replaced the KT120 mono blocks with the Mini Watts and the main preamp with a fully passive one tonight. Then I listened to some demanding music. Pink Floyd, Goldfrapp and Kraftwerk. The Minis did great on my Martin Logan ESLs. Super clear, super clean and really precise sound stage. Definite overachievers. No slouch on loudness either.

Good listening
Bruce

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PostPosted: 15 Jul 2014, 10:43 
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Joined: 31 Aug 2011, 12:47
Posts: 3
I'm looking for the "three pin ribbon connector" used for the lm317. I've looked on mouser for these, but there's so many different types of connectors. It's hard to tell whats the size. Anyone have a part number?


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PostPosted: 16 Jul 2014, 11:10 
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Joined: 04 Jun 2008, 20:59
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Location: Arizona, USA
Hi. Pretty much any will do. You can of course solder the 317 to the board as long as you use a heat sink on it. I used the three connector arrangement in this project (and a few others) as the chassis would be sufficient for a heat sink source. In the big amps this in not feasible as the 317s will be dissipating considerably more heat.

You can make your own three conductor connectors with the pin type in line sockets for use with PCBs. They often come in a strip and you cut off as many as you need. The actual connections are usually soldered then inserted into the connector.

Good listening
Bruce

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PostPosted: 05 Aug 2014, 16:41 
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Joined: 05 Aug 2014, 16:37
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I am pretty new to this but is there a list of all the components for this project somewhere, I know I can take them off the schematic but I don't know what brands or anything like that to buy. Any help is appreciated.


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PostPosted: 07 Aug 2014, 14:30 
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Joined: 23 Mar 2014, 17:14
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Hi,
I'll let you know what I've used. The best is to get the components of the schematic, this helps studying it as well.
I used Vishay Beyshlag metal film resistors for the most of it, except for the power resistor, which is Vishay Dale and few no name carbon films in the power supply. Caps are Solens and F&T for the power supply, which I had in my stash anyway, russian NOS K40 as coupling caps and Nichicon bypass. LR8 is available from Supertex only and LM317 is commonly available from a number of manufacturers. Diodes are Fairchilds, AFAIR.
The result sounds great by common opinion :)
Niki


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PostPosted: 07 Aug 2014, 16:56 
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Joined: 04 Jun 2008, 20:59
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Location: Arizona, USA
Hi, It is a surprisingly good sounding amplifier. More power that the output level would suggest as well. I use mine on those occasions when the KT120 amps are excessive. This is a problem I have here as a designer. I have all the prototypes and some of the pre-production commercial ones. I have no idea of how many amps I own. There just isn't enough time to play them all. However, I need to have them around so that I can assist folks that might have build problems. Then I can help them trouble shoot better. All in all though the number of build problems are rather few. The designs were intended that way. BTW, the original Oddwatt KT88 amps that are in the posted project are still going strong and still are using the original tubes. I have updated them to match the most current versions though.



Good listening
Bruce

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