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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 Sep 2012, 11:46 
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Location: Vänersborg, Sweden
Here's a VERY good example how this can be solved: http://www.jogis-roehrenbude.de/Verstaerker/SRPP-VV/1a.jpg


Here's the whole Chottabloongi: http://www.jogis-roehrenbude.de/Verstaerker/SRPP-VV/SRPP-VV.htm

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PostPosted: 21 Sep 2012, 13:49 
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Joined: 14 Aug 2012, 23:44
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Location: Australia
Thanks Magnus. Just about how I had it drawn, a voltage divider with a capacitor across the lower resistor in the divider, connected to the +ve rail of the heaters and removing the ground from the heater circuit. This one simplifies it though, by just putting the divider right at the end of the circuit. I will try this and see how it goes.


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PostPosted: 21 Sep 2012, 14:03 
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You're welcome.

I think I have seen or read that about hooking up the heater to cathode polarity, but I may be mistaken in this.

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PostPosted: 04 Nov 2012, 05:19 
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wow hasn't this come some way in the months i've not been around. great stuff!

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PostPosted: 04 Nov 2012, 07:34 
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Some revelation about the "can we float the heater voltage". In a word "yes". There is no need for the heater voltage to be connected (or associated with) to the HT. The heater voltage can float. In the past I have not been able to use metal power plugs and sockets (for the 24VAC wall wart). When connected to metal chassis or enclosure preamps this cannot be done because one side of the AC plug pack is connected to the DC of the filament supply and the plug pack goes BANG!

Float the filament voltage, earth the negative of the HT+ to the chassis of the metal enclosure, a use a metal power socket and all should be fine. I'm about to assemble one and if I'm wrong I'll let you know. For an image of my latest 4S Universal take a look on the dedicated link http://www.diyaudioprojects.com/Forum/download/file.php?id=5091&mode=view

I have started a thread just for the 4S Universal jump to here: http://www.diyaudioprojects.com/Forum/viewtopic.php?f=9&t=4087

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PostPosted: 28 Dec 2012, 20:18 
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So a simple question for those whom have built these preamps. Which sounds better, the 4S III specifically designed for the 12AU7 or the 4S "Universal" with a 12AU7 installed?

I am looking to install one design or the other in an amp where a moderate gain is required and would like other people's opinions on the matter.

Thanks.

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PostPosted: 29 Dec 2012, 01:55 
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For me the 4SMKIII The Black was the best sounding. I also think the 12AU7 is a better sounding tube for Hifi if you don't need the extra gain.

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Projects: "Lagoon" - tube preamp with cathode follower | "retro-Oatley 6J6" - 6J6 push-pull headphone amp with OPTs | "retro-Hiraga" - Jean Hiraga Le Monster
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PostPosted: 25 Jul 2013, 08:47 
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Joined: 05 Jun 2012, 13:10
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Location: Darboy, WI, USA
I was thinking about building another 4s IV, but a stand alone preamp this time. The tube depot has a power transformer that looks, to me at least, to be a perfect match: http://tubedepot.com/tr-pw-13.html

Any comments?
By the way, my current 4s IV is driving my 6aq5 amp and I'm loving it. Thanks Matt and Mark for driving this design.

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PostPosted: 25 Jul 2013, 18:49 
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RossD: I think the current rating of the tranni is too low. If you used two it maybe OK. You want to develop about 260V and be able to provide about 2mA per channel. So you may need a tranni which will provide at least 4mA. Correct me if I'm wrong I haven't built a small preamp for a while.

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PostPosted: 25 Jul 2013, 21:50 
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RossD wrote:
The tube depot has a power transformer that looks, to me at least, to be a perfect match: http://tubedepot.com/tr-pw-13.html
Personally, I would spend the extra $2.51 and get this one (Edcor XPWR136-120) instead. The voltage is higher and center tapped, it supplies up to 60mA so current is no problem, and it has lots of 6.3v filament current. This is my "go-to" transformer for small tube circuits of all kinds. I would also bet that the quality is a lot higher than the one from Tube Depot. There is also this one (Edcor XPWR164-120) for just $7.08 more if you wanted to use a 6CA4 rectifier (with the separate 1A dedicated filament winding).

Just my opinion but I really like Edcor transformers (both output and power).

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