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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: 05 Jan 2014, 14:04 
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Joined: 09 Jul 2012, 14:49
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Thanks again. Can you explain how these resistors work in relation to the load the preamp sees or is this a dumb question?
John


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PostPosted: 08 Jan 2014, 13:35 
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In relation to the output of the preamp the resistors makes the load less reactive (capacitive) and more resistive. If both (3,4,5...) outputs are connected simultaneously, the capacitive impedances of the interconnects are summed and the resistors serve not only the role of isolation the output of the amplifier, but also isolation of one interconnect from the other.


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PostPosted: 10 Jan 2014, 18:35 
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Joined: 04 Jun 2008, 20:59
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Location: Arizona, USA
Thanks for answering, I missed this one.

Good listening
Bruce

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PostPosted: 15 Sep 2014, 19:40 
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gofar99 wrote:
Thanks for answering, I missed this one.


Hi gofar99

I need your help. what is the voltage B + "ForeWatt ECC802S SRPP Preamplifier Schematic". I started making up the "12AX7 Valve preamp power supply" you made earlier, when it was found that his new project and decided to move to ele.Then I would like to use the font that started to the other, but have it in your output 260 volts.How can I use it? For this filament is easy.I just need B +
Thank you so much.
Luiz


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PostPosted: 16 Sep 2014, 09:21 
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The raw B+ at the rectifiers is approximately 250V. By the time it is filtered and reaches the tube anodes it is in the 195-225 range depending on the efficiency of your filters. The target range is 200-205, but anything in that range is fine. If you go over 225-230 up to about 250 you will need to change all the cathode 680R resistors to 820R. There is no advantage to the higher B+ though.

Good listening
Bruce

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PostPosted: 30 Oct 2014, 09:17 
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Joined: 29 Oct 2014, 12:32
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Location: Russia Komi republic
Greetings!
Firstly, Thank you, Bruce, for your work!
I have heard many good reviews about the preamp and want to to build it.
I have read all 33 pages and found several schemes preamp. With different parts.
Due to some problems with the English language (I'm from Russia) I do not understand some things. I'll ask about them in the manufacturing process.
But now, my first question is - can you put me to the scheme.
I do not know how to say it right ... the current version. Or the latest stable version. Or just the last great sounding version). I'm going to buy the parts and I need to know - what is it? I hope you understand me correctly.
Thank you again!

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PostPosted: 30 Oct 2014, 14:47 
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Hi, Things like the preamp get refined over time and yes there are a few changes. The best all around version is the one below. It is used in the commercial kits. You can use a different power supply as long as it provides a very clean 200-225 volts to the tube anodes. It need not be regulated, but the LR8 regulators allow for easy voltage adjustment and add filtering. Each anode needs to be separated from the other by at least one filter section to minimize crosstalk between the channels. You need to provide an isolated from the ground 6 volts (could use 12 if convenient) DC to the heaters. An finally a 65-75 volt positive DC voltage to mix into the heater circuit (a tap off the main B+ works well). This voltage protects the driver tube from failure and reduces the noise level slightly. Changing the coupling capacitors ( I use K40Y9 ones) will slightly alter the "flavor" of the sound. Pick good ones if you have favorites.

EDIT: Ignore the different voltages shown at the output of the LR8 regulators it was a misprint. Also if you wish you can eliminate the passive relay switching portion and if you don't mind leaving the tubes powered all the time can substitute a 4PDT switch. I leave my tubes powered when I use the passive mode (rather seldom do I use that mode).

Good Listening
Bruce
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Preamp PS April 13 2011B.jpg
Attachment:
Preamp main Feb 26 2011.jpg


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PostPosted: 31 Oct 2014, 03:50 
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Location: Russia Komi republic
Thanks!

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PostPosted: 31 Oct 2014, 08:00 
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If I decide to do Xlr output, I have to add to the output transformer? Maybe someone has already thought about such a solution?
The fact that my amp has the Xlr input and sounds much better through it.

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PostPosted: 31 Oct 2014, 08:39 
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H, the circuit was not designed for XLR use and can not easily be adapted for such. As is you would need to obtain a matching transformer to do what you want. I would suggest something in the order of 50-100K input to XX to match your input impedance. It will color the sound. How much is uncertain. I would try it direct first. BTW, Edcor has a line of such transformers and they are rather inexpensive.

Good listening
Bruce

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