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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: 21 Feb 2017, 13:00 
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Joined: 04 Jun 2008, 20:59
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Location: Arizona, USA
Hi, A better choice for tubes in this case is the 6DJ8. With 820R cathode resistors and a 100uf capacitor on the lower one the gain will be 29. But more importantly the output impedance is only 1.49K. A 12AX7 is not suitable as the output impedance with a cap is 13.6K and with out 18.8. A 12AT7 is not all that good either. With 220R resistors the gain with capacitor is 25 with a Zo of 3.4K, no capacitor the values are gain of 17 and a Zo 0f 4.3K.

Good listening
Bruce

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PostPosted: 22 May 2017, 19:35 
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Joined: 07 Sep 2011, 20:55
Posts: 24
Location: Longmont, Colorado
After a very long delay in finishing my sons Forewatt, I finally completed it a month ago and he is the new proud owner of it. The sound is truly amazing! just enough lush warmth to satisfy my desire for what I grew up with (Mcintosh and Marantz tube gear) combined with dead quiet, crisp, clean, accurate reproduction.

Thanks to all for your help and patience during my many posts of questions. Now on to build him (and one for me) a couple of Groovewatts.

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PostPosted: 22 May 2017, 20:26 
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Location: Arizona, USA
Hi, I'm glad it worked out for you. That is really nice wood. Tiger maple by any chance?

Good listening
Bruce

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PostPosted: 23 May 2017, 17:39 
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Joined: 07 Sep 2011, 20:55
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Location: Longmont, Colorado
Yes it is. It's some very old German flamed maple that was left over from an acoustic guitar build a few years ago. It's around 3/16" thick glued to 1/2" baltic birch ply. Finish is hand rubbed shellac french polish.

I'll see if I can build a twin of this for the Groovewatt.

Allen


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PostPosted: 26 May 2017, 12:53 
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Joined: 26 May 2017, 02:39
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hi guys!
First of all thank for sharing this project and your experiences with it. I found all very instructive
I am a new bee that like to try so I did use this pre amp as pre section in my kt88 se amplifier building.
Basically this is the first stage leading to the power stage (kt88).All in one enclosure.
It worked out pretty well and I am happy about the quality of the sound but...I really need little more gain to drive the kt88.Can I change the 12au7 with some other tube so that I can finally properly drive the power tube? obviously I would like the modification to be kept at minimum
thanks for help


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PostPosted: 27 May 2017, 10:04 
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Hi, Yes you can get more gain. Either post or PM me the schematic of exactly what you did including the power supply. Other tubes can be used in the design with minimal changes. But Just plugging in some can have unexpected results. How much more gain do you need?

Good listening
Bruce

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PostPosted: 02 Jun 2017, 17:20 
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Joined: 18 Jan 2017, 18:55
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I am working on a parts list to build a Forewatt preamp. Any suggestions for a regulator/variable resistor to go with the LR8N, looked on Mouser but there is too many choices for me, not sure how many poles ect?
Chace


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PostPosted: 02 Jun 2017, 20:49 
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Location: Arizona, USA
Hi, I don't understand your question. The LR8 is a regulator. There are three variations of it. All are electrically the same. I prefer the LR8K4 as it is a bit more robust but it does require soldering to pads (it has no lead wires) as it is a flat pack device. I use "surf" boards for it. Fasten it to the surf board and either solder that to the main board or stick it in an IC socket. Two fit nicely side by side. The LR8N3 is like a small transistor and is easy to use. It has a lower power rating though. One per channel on the Forewatt works fine though. The final version is a surface mount device. I forget the designation. It can be difficult to use as it is tiny. It has a power rating in between the other two. Fine if you don't mind using SMDs.

Good listening
Bruce

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PostPosted: 12 Jun 2017, 13:28 
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Joined: 29 Oct 2014, 12:32
Posts: 95
Location: Russia Komi republic
Hi!
Just want to share photo of my new preamp.
Yes, this is not FOREWATT as is. poty design :)
This is a balanced version of SRPP with CCS in cathodes, tube rectifier and choces in power supply and remote control with display.
But forewatt was my first build and point of beginning my DIY way.
And forewatt show me, how SRPP sounds. Great!
Thanks, Bruce for SRPP for us :)
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PostPosted: 12 Jun 2017, 21:09 
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I'm glad to have started you on the way. I have afew "ForeWatts" that are more than the originals. One that resides in my system is in the photo. It also has a "Groove" phono section. All tube except fo r thr digital remote/volume control.

Good listening
Bruce
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