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4S Universal Tube Preamp Project (12A*7)
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Author:  mwhouston [ 23 Jun 2018, 02:38 ]
Post subject:  Re: 4S Universal Tube Preamp Project (12A*7)

http://psvanetube.com/wordpress/store/products/treasure-globe-6sn7-se-pair-gf-limited-special-edition/

I swore years ago I'd never buy another tube having way way too many but when these came along....

And a limited series, should buy two pairs. Might be good for the 6SN7 single stage preamp Suncalac designed. Or even much better (listening Suncalc) a two stage 6SN7 with cathode follower stage. Now wouldn't that be nice. Especially seeing you could use two of these glorious tubes.

Author:  jocelys1 [ 28 Jun 2018, 01:26 ]
Post subject:  Re: 4S Universal Tube Preamp Project (12A*7)

Finished the 4S. Tesla 6CA4 for the rectifier and the signal tube is a Mullard 12AT7WA (CV4024).

Initially, it had a very bright unbalanced sound, but with a run-in of about 30 hours, it sounds damn good.

I've also tried a 12AU7 (Electronics for medicine - 029), which sounded good from the beginning. Different sound though, more laid back. I prefer the mids on the ATs.

The 4S is hooked up to a Brook12A clone, running 2A3s in PP. The system sounds beautiful. Both are new and therefore require some more run in to sound their best. It improves every day and I'm not complaining..:)

Matt, fabulously simple design. Thank you. We are waiting for the 2-stage 6SN7 design....:)

Author:  mwhouston [ 28 Jun 2018, 03:47 ]
Post subject:  Re: 4S Universal Tube Preamp Project (12A*7)

Yes Matt (please) two stage 6SN7 with cathode follower. For those 6SN7-SE tubes I have ordered.

Thanks mate.

Author:  Suncalc [ 30 Jun 2018, 19:07 ]
Post subject:  Re: 4S Universal Tube Preamp Project (12A*7)

mwhouston wrote:
Yes Matt (please) two stage 6SN7 with cathode follower. For those 6SN7-SE tubes I have ordered.
OK Mark, I have a design. But you'll have to give me a few days to do some prototyping. I want to see how it performs.

Author:  mwhouston [ 30 Jun 2018, 19:41 ]
Post subject:  Re: 4S Universal Tube Preamp Project (12A*7)

Suncalc wrote:
mwhouston wrote:
Yes Matt (please) two stage 6SN7 with cathode follower. For those 6SN7-SE tubes I have ordered.
OK Mark, I have a design. But you'll have to give me a few days to do some prototyping. I want to see how it performs.


Well the tubes are on the ocean so take your time. Thanks a bunch. I'm sure we will all benefit.

Author:  jocelys1 [ 01 Jul 2018, 19:48 ]
Post subject:  Re: 4S Universal Tube Preamp Project (12A*7)

mwhouston wrote:
Suncalc wrote:
mwhouston wrote:
Yes Matt (please) two stage 6SN7 with cathode follower. For those 6SN7-SE tubes I have ordered.
OK Mark, I have a design. But you'll have to give me a few days to do some prototyping. I want to see how it performs.


Well the tubes are on the ocean so take your time. Thanks a bunch. I'm sure we will all benefit.


Matt H. and Matt R., thank you. We are grateful.

Author:  mwhouston [ 01 Jul 2018, 22:36 ]
Post subject:  Re: 4S Universal Tube Preamp Project (12A*7)

That was quick. The 6SN7-SE have arrived. Just wondering if we should not start a new thread for 6SN7 cathode follower preamp? Not cheap at $A382 but how good looking. These babies will really have to standout on any build.
Attachment:
6SN7-SE (666x800).jpg

Author:  Woodo [ 02 Jul 2018, 17:22 ]
Post subject:  Re: 4S Universal Tube Preamp Project (12A*7)

Suncalc wrote:
Alex Q wrote:
Do i need to isolate the Transformer from the chassis?
Nope.

Power transformers are all HI-Pot tested these days and transformer microphonics is practically non-existant in modern units. Personally I always make sure I have a good ground between the chassis and the transformer end bells. This just makes shielding that much better and provides a guaranteed ground path in the event of catastrophic transformer failure. The industry chassis ground bonding standard is 2mΩ.

Matt, are there any diagrams available to show how to ground the transformer end bells or grounding in general. I did read Bruce's articles which are helpful however drawings or images would fill some gaps for me. Woodo.

Author:  Suncalc [ 02 Jul 2018, 18:34 ]
Post subject:  Re: 4S Universal Tube Preamp Project (12A*7)

Woodo wrote:
... are there any diagrams available to show how to ground the transformer end bells or grounding in general.
I use the screws as a current path to the aluminum top plate of my amps. This is the type of hardware I use.
Attachment:
Screw_and_washer_no_8.jpg

It's really simple. Directly under the head of the transformer mounting screw, put a toothed lock washer. This lock washer has tabs that will bite into the transformer end bell foot (penetrating the paint) and the underside of the head of the screw. Then, against the underside of the top plate place another lock washer between the top plate and the nut. This will create a good connection between the nut and the top plate. The arrangement should look like this.
Attachment:
Screen Shot 2018-07-02 at 4.29.41 PM.png

In this way the end bells are completely grounded to the top plate and no wires are involved.

Hope this helps.

Author:  Woodo [ 02 Jul 2018, 21:52 ]
Post subject:  Re: 4S Universal Tube Preamp Project (12A*7)

Thank Matt that helps a lot.

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