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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: 30 Sep 2010, 16:05 
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Joined: 04 Jun 2008, 20:59
Posts: 3856
Location: Arizona, USA
Hi, Glad to be of value to you all. I just design stuff I like and then post it for others who may also like it. My latest ( a tube phono preamp) is nearly ready. BTW (not to hi-jack my own thread) I have a Marantz 2265B. 2250, 1060 and CD5001 (modded). Nice stuff if you do SS. Me I have moved on - or as some would say moved backwards. All tube gear now except an OPPO 83SE.

For those building the Forewatt, I suggest that you check the voltages at the mid cathodes and bottom cathodes to see how close one channel matches the other. I have found that a number of 12AU7 variations have poor gain matching between the two triodes. Ideally they should be equal. Up to about 10% error seems fine and is not audible. Above that it might be slightly noticable in gain of the stage. This could throw off your channel balance. I have found the JJ spiral filament tubes to be fine. Some NOS and other brands have been off. So if you have different gain between the two channels make the test. If you really want to splurge, get tubes matched for gain. This is often only a few $$ more and should eliminate the problem. Tube aging does not appear to be significant as mine now have many hours on them and are still perfect.

Good listening
Bruce

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PostPosted: 30 Sep 2010, 17:27 
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Joined: 28 Oct 2009, 02:34
Posts: 501
Location: Utrecht Nederland
Hi everybody,

I will start shortly to build my friends ForeWatt, this time using the right tubes and I will stick strictly to schematic. His has to work good, he's got Klipsch speakers, 97 dB, so stuff I build for him really has to be noise free. He has my ForeWatt right now and loves it, just the more he will like his own, it's gonna be the better amplifier. I will post pics as I progress. All the best.

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Greetings from Holland, Ben

My DIY Audio Projects:
- Single-Ended 12B4A tube amp with ECC802S driver
- DIY Push-Pull KT88 tube amp (OddWatt amp from scratch)
- 832 / GU32 tube push-pull amplifier project


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PostPosted: 01 Oct 2010, 22:26 
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Joined: 04 Jun 2008, 20:59
Posts: 3856
Location: Arizona, USA
Hi, The Forewatt if built correctly can easily go into the sub 90 dbv S/N range. Two of mine show better than -93 which is essentially the noise floor in my shop. The design can be adjusted for various tubes, but the best I have found are the long plate versions of the 12AU7 particularly the JJ ECC802S. My personal experience is that 6SN7s which would seem a natural for the circuit tend to be much noisier. I have yet to try 6CG7s and their offspring as they might be good in it as well.

Good listening
Bruce

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PostPosted: 05 Oct 2010, 00:24 
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Joined: 28 Oct 2009, 02:34
Posts: 501
Location: Utrecht Nederland
Hallo everybody,

I am going to start to build my friends ForeWatt very shortly, he has mine in use right now and he loves it. His speakers are very sensitive, Klipsch with 97 DB 1 watt 1 meter, so whatever I have to build for him, it has to be noise free. This time I will buy a matched pair of EEC802S. Those tubes are known to work great in this amp, and I don't want to have to go through the same hassle I had to go to making my pre amp work with the Russian 6SN7's. Those are very noisy tubes, sounding sweet though, but the noise level is almost unacceptable, especially for a pre amp. Mine is now quiet enough, but it was not easy to get there. It is right now driving my friends marantz amp hooked up to his very sensitive Klipsch speakers and he don't complain about noise, just the more will he love his own pre amp I am just about to build. I will post pictures as I progress.

Thanks Bruce, for answering my never ending stream of stupid questions, I wouldn't be able to do what I do without your knowledge and ideas. I highly appreciate you.


All the best.

_________________
Greetings from Holland, Ben

My DIY Audio Projects:
- Single-Ended 12B4A tube amp with ECC802S driver
- DIY Push-Pull KT88 tube amp (OddWatt amp from scratch)
- 832 / GU32 tube push-pull amplifier project


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PostPosted: 05 Oct 2010, 05:43 
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Joined: 14 Feb 2010, 13:13
Posts: 663
Location: Lisbon, Portugal
I haven´t tried the following tubes, but people do seem do be extremely satisfied with them:

1st: GE 5 Star 5814A
2nd: Amperex 7316

I have no way to try out these, but i´m very curious with the GE 5 star tube! :)

Cheers,
Miguel


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PostPosted: 06 Oct 2010, 00:04 
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Joined: 28 Oct 2009, 02:34
Posts: 501
Location: Utrecht Nederland
Hi everybody,

I will try the 6N1P in this amplifier, this is at least the same tube socket as the EEC802S, so if it won't work 100 % satisfactory, I can just roll tubes and adjust some values and good it is. I had so much headache making my first build work and quiet enough, I hope this one will make me less trouble. I will post pics soon.

_________________
Greetings from Holland, Ben

My DIY Audio Projects:
- Single-Ended 12B4A tube amp with ECC802S driver
- DIY Push-Pull KT88 tube amp (OddWatt amp from scratch)
- 832 / GU32 tube push-pull amplifier project


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PostPosted: 17 Oct 2010, 17:23 
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Joined: 03 Jan 2009, 10:44
Posts: 121
Hello, friends,

I guess I'm too busy with work and home. I know because I'm now planning to build another piece of audio gear...this preamp. Reading Bruce's writeup, I am convinced I need just the right output capacitor: the 1 uF Russian K40Y9 paper-in-oil (PIO) capacitor. Only problem is that I can't find a pair. Any suggestions on source or near-equivalent alternatives? Thanks in advance for your help!

Regarding the source for the remote controlled volume control: Ben, I'm intrigued by your mention of an alternative to the one from Hong Kong. Where do I order a "Rebecca?" And what is the part number?


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PostPosted: 17 Oct 2010, 20:54 
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Joined: 28 Oct 2009, 02:34
Posts: 501
Location: Utrecht Nederland
Hi everybody,

Rebecca is my spouse and this was supposed to be a joke! Am I the only one laughing about it? :D

All the best.

_________________
Greetings from Holland, Ben

My DIY Audio Projects:
- Single-Ended 12B4A tube amp with ECC802S driver
- DIY Push-Pull KT88 tube amp (OddWatt amp from scratch)
- 832 / GU32 tube push-pull amplifier project


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PostPosted: 17 Oct 2010, 22:05 
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Joined: 03 Jan 2009, 10:44
Posts: 121
I got it the first time, Ben, and had a good laugh. I just couldn't resist the question, though.

So I guess you're saying Rebecca does not have a part number???

Lofton


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PostPosted: 29 Oct 2010, 21:21 
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Joined: 29 Oct 2010, 20:53
Posts: 1
Bennybuis wrote:
here is the beginning of my ForeWatt pre amplifier, the Dutch version. Things are going slow, since I am very ill, but I am happy about how it turns out. I am using vintage cloth wire for the first time, difficult to work with, but very nice.

Hi Ben, i'm newbie here, is it possible to share the PSU PCB lay-out? hope it is ok. Thank you so much. gynco


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