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Old 23rd August 2009, 12:29 AM   #1
Pocoyo is offline Pocoyo  Indonesia
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Default asking about 6sn7 and 2a3 tubes

hi

my friend buy 4 tubes driver 6sn7 and 2 tubes power 2a3
now he ask me to help him make it to a tube amplifier
i think i want to build them in the pcb (easier) not hard wiring
can you help me where i can find the article / the pcb

thank you
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Old 23rd August 2009, 01:33 AM   #2
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Quote:
Originally Posted by Pocoyo View Post
hi

my friend buy 4 tubes driver 6sn7 and 2 tubes power 2a3
now he ask me to help him make it to a tube amplifier
i think i want to build them in the pcb (easier) not hard wiring
can you help me where i can find the article / the pcb

thank you
Are you looking for 2A3 amp info or how to make pcb info? If it's amp, here is one I've built. It sounded good.
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Old 23rd August 2009, 03:51 AM   #3
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I would think it would be harder to build with a PCB, not as easy to make changes or upgrades to the circuit. I would suggest though if he wants to use the 6SN7 + 2A3 to do a cascaded 6SN7 into the 2A3, like the Sun Audio SV-2A3, and countless other 2A3's and 300B's.

If he can get his hands on some 12AT7's I would check out the Baby Ongaku. However, the 6SN7 + 2A3 would probably provide the easiest and cheapest path to success. I would avoid the PCB for such a simple design, but just my 2 cents.

Cheers

James

edit: If you want to use a PCB and you can get them shipped there you could look to the Tubelab SE, however it uses the 417A for input duties. (www.Tubelab.com)

Last edited by JPeitzman; 23rd August 2009 at 03:56 AM.
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Old 23rd August 2009, 04:50 AM   #4
Pocoyo is offline Pocoyo  Indonesia
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thanks evenharmonics & james

sun audio sv2a3 would be nice
want to use pcb just for take a minimum risk
can you give me a link for sun audio schematic?
Thank you
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Old 24th August 2009, 02:15 AM   #5
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Here are a few to think about, Sun Audio is first

http://www.goodsoundclub.com/Site_Im...o_VT-2A3_3.JPG
http://www.jeack.com.au/~lucas/2A3AL.jpg
http://webspace.webring.com/people/d...tics/quest.gif (think 2A3 instead of 300B)
http://home.earthlink.net/~ivol/moon..._schematic.jpg

I know there are now values for the Moondog above, but it will give you an idea, mostly the same as the others. This may be of interest:
http://home.earthlink.net/~jeremyeps...f/sp15_2a3.pdf

and this:
http://www.tubecad.com/2006/03/aikido_se_amplifier.png

Cheers

James
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Old 24th August 2009, 07:35 AM   #6
Pocoyo is offline Pocoyo  Indonesia
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thanks james

oh yes just a simple question,
is there easy to wiring one by one cable ?

what kind of cable i must use ?
silver, silver coated or copper cable ?
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Old 24th August 2009, 07:55 AM   #7
rutcho is offline rutcho  Bulgaria
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Sun Audio SV-2A3 the schematics from the first link, given by James is my favorite one. I recommend a higher value of anode load. Very successful choice is Hashimoto H-20-3.5U connected to 3.5 KOhm load.
Pocoyo, to make things easy, you can use terminal boards with mounted tube sockets.
From partsconnexion - IAG-68070 and IAG-68067 for mono operation and IAG68071 IAG68068 for stereo.
Similar boards can be found in http://www.tubesandmore.com/
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Old 24th August 2009, 11:22 AM   #8
Zoran is offline Zoran  Serbia
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sorry but that from sun audio is not good at all
first, the value of pot 100k is too high for the 6sn7
right value if pot required is 25K...
next the values of Rload at anodes of 6sn7
are too high value.
The load line will be almost horizontal.
and the drop of voltage is probably large,
so the resulting Va will bi lower voltage,
against higher voltage that
should be like Va when we talk about the 6sn7...
next, the device will have more than sufficiant gain,
like common fassion in that design, so the pot most
of the time will be at lower positions causing loss of highs.
*
that is from the first sight cheers
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Old 24th August 2009, 11:45 AM   #9
rutcho is offline rutcho  Bulgaria
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Yes, Zoran, the input should be corrected.
First, it is absolutely necessary to add a grid resistor to the first triode of the 6SN7. Otherwise in case of bad contact in the input attenuator the grid of this tube will "hang". The value of grid resistor shold be about 220KOhm. The value of 25 KOhm for the pot is fine. There is no problem with 47KOhm as well.
The input sensitivity is about 250mV for full power. If a lower sensitivity is necessary, an additional input attenuator can be applied. The reserve of gain can be used for NFB as well (for those who admit it in the SE stages).

Last edited by rutcho; 24th August 2009 at 02:55 PM.
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Old 24th August 2009, 11:22 PM   #10
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I would lose the pot all together, just put a resistor to ground and use is as just a stand alone amplifier. I posted these because of the fact that the future owner of the amplifier already has the 6SN7's and 2A3's. However if it where I, the 6SN7 cascade would not be my choice. I would try very hard to find a couple of 6SL7's to serve as input tube. With these I would build up something like the Morrison Micro:
http://www.the-planet.org/images/2A3--6SL7_small.jpg
Much simpler design, losing some capacitors (including a coupling cap), and in general losing one entire triode section. I would then use the 6SN7's to build a simple line amplifier. Search around for Frank's 6SN7 and 6SN7 versions of the Bottlehead Foreplay.

As for wiring, I would use component leads where ever possible. Us terminal strips as suggested above by Rutcho. Otherwise I would 24awg to 20awg (roughly) solid core copper or silver, which ever. Just use the shortest runs needed, high quality passives, and high quality Teflon or cotton insulated wire and you will have a good build. Most of all, use high quality solder with good technique to ensure good solid joint. Make sure too that you use the highest quality output transformer you can afford.

Cheers

James
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