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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: 24 Sep 2016, 19:25 
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Joined: 20 Feb 2014, 10:35
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Location: NZ
My second version of the 4S. After some discussion with Matt, to reduce gain the volume pot (50K) is on the input with 250kΩ resistors. Fitted with 2 inputs, switch for selecting heaters for 12A** & 6A** tubes and uses an octal rectifier, either 6X5GT, 5852, 6AX5GT or with adapters 7Z4 or 6BY5GA.

More volume control range now, running from around 10 o'clock to 2 o'clock at average listening levels. More depth & detail in the music too, can pick out those little details which were a bit veiled in the 1st version.


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PostPosted: 24 Sep 2016, 21:29 
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Joined: 06 Jun 2008, 18:23
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Location: Australia
Looks neat.

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PostPosted: 27 Nov 2016, 07:20 
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Joined: 27 Nov 2016, 07:15
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Location: Holland
Hi, i built this preamp exactly as shown and it sounds great. One problem though, i tried about 10 12a.7 tubes, and every time the same channel is much louder then the other. Am i missing something?

Thanks,
Daniel


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PostPosted: 28 Nov 2016, 19:23 
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If the problem is consistently in the same channel, I would suspect a passive part. Check the resistors, but your input potentiometer is the more likely source.

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PostPosted: 28 Nov 2016, 20:31 
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I've even miss-read a meter reading once and mistook 2.7K for 27K! Fortunately it was obvious when I played the unit. It just sounded wrong.

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PostPosted: 20 Dec 2016, 19:46 
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Joined: 08 Feb 2016, 20:02
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I have built this unit and it sounds awesome!! I'm not an expert but I have built a few things. Just wonder what kind of mods could be done to make this work for a phono preamp?


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PostPosted: 24 Dec 2016, 16:17 
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Aazero wrote:
I have built this unit and it sounds awesome!! I'm not an expert but I have built a few things. Just wonder what kind of mods could be done to make this work for a phono preamp?

There are a number of phono preamp cct. around. I'd follow them. I've built a number of tube phono preamps. Apart from some more caps and generally two stages there is not much more in it.

Merry Xmas.

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PostPosted: 31 Dec 2016, 02:20 
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Joined: 29 Dec 2016, 14:54
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Quote:
After some discussion with Matt, to reduce gain the volume pot (50K) is on the input with 250kΩ resistors.

Do you have a schematic or drawing for the volume on the input and the 250K resistors?

Thanks
Bonsaimaster


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PostPosted: 31 Dec 2016, 08:01 
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Joined: 20 Feb 2014, 10:35
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Location: NZ
Sure, like this. R4 is the 250KΩ resistor & R3 is a 50KΩ potentiometer. R5 is also 250KΩ.
Attachment:
Revised 4S Pot Input.jpg


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PostPosted: 03 Jan 2017, 02:44 
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Joined: 01 Jan 2017, 17:20
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Location: Australia
Hello, This look like a very nice project, I am new to tube building and to Australia, I am interested in building the 4S any suggestion for a good part supplier in Australia, mainly for transformer.


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