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PostPosted: 20 Mar 2009, 18:57 
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Joined: 26 Aug 2008, 20:57
Posts: 415
Location: Atlanta
I just got some wire from this company:

http://www.wesbellwireandcable.com/

Silver plated, teflon coated MIL-SPEC wire for $18.95 for 100'


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PostPosted: 26 Mar 2009, 06:28 
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Joined: 26 Mar 2009, 05:45
Posts: 2
Location: Switzerland
Hi everyone!

I'm new on tube amplifiers, and intend to build the K-12G. What do I need to change when using 240V?

Thank you,
Wolfgang


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PostPosted: 26 Mar 2009, 11:48 
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Joined: 02 Mar 2009, 12:41
Posts: 1051
Location: Vänersborg, Sweden
You have to be sure that the power (or mains) transformer is wired for 230V.

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“If you don't know where you are going, any road will get you there.”
―Lewis Carroll


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PostPosted: 26 Mar 2009, 12:08 
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Joined: 28 May 2008, 21:53
Posts: 4559
Location: Winnipeg, CANADA
Hi Wolfgang,
The transformers are 120V primary, so you will need to use a step down transformer to go from 240V down to 120V. 1A will be sufficient.

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PostPosted: 20 Apr 2009, 14:33 
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Joined: 20 Apr 2009, 13:49
Posts: 5
Location: Switzerland
Hello,

So for changing the transformer to 220V which voltage should i look to have on the second winding?
Looks like 12V on Sa1-Sact (inverted phase Sa2-Sact?) , what sould be on Sb1-Sb2?

Thank you,
Oleksiy


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PostPosted: 20 Apr 2009, 15:47 
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Joined: 20 Mar 2009, 14:26
Posts: 4
Location: Canada
Simon Yuen wrote:
After I read the reviews of the K-12 M/G Amp, I want to build one too.
Right after the above posting, I ordered the K-12G kit from Tube Depot. They replied in back-order, and used to due 1 to 2 weeks. However, it is one month now, still no sign on K-12G kit. :| If you want to order it, prepare for the long waiting.
Simon


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PostPosted: 01 May 2009, 20:41 
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Joined: 04 Jun 2008, 20:59
Posts: 3749
Location: Arizona, USA
Hi Everyone, I'm glad to see the interest in the K-12. Mine is in my office and drives a pair of Klipsch KG4s every day. I saw a question some posts back on the use of different output transformers. The originals are not bad, a little deficient in overall response but OK. There a few upgrades that are worthy and not costly. The specs that you want are either 10K or 8K center tapped primaries with at least an 8 ohm secondary. A 10 watt rating is sufficient. There are pros and cons over which of the two primaries to select. I used 10K. The secondary should be 8 ohms but can go down to 6 without problems. At 4 ohms it will be necessary to recalculate the negative feedback loop values as they are affected by the level of signal at the output terminals. I would go for only transformers with 40% ultra linear taps. This will further improve the sound and lower distortion. The penalty is a slight reduction in output. IMHO a very worthy trade. The rewiring required to use the is simple. The transformers I would recommend in order of price are
EDCOR GXPP10-6-10K. About $22. This is a trannie designed for guitar amps but works very well in hi-fi circuits. It has a single 6 ohm secondary and has tab terminals - not wires.
EDCOR CXPP25-MS-8K About $45 This is my first choice. A big transformer and good for a lot of power, excellent bandwidth etc. I use them in class A amps up to 25 watts, they can do more. 4,8 and 16 ohm secondaries.
Hammond 1610 and 1608 (I believe these are the numbers) About $45 as well. Rated 10 watts one is a 10K and the other an 8K. Rather good trannies, physically in between the sizes of the EDCORS.

Good listening
Bruce

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PostPosted: 07 May 2009, 15:26 
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Joined: 20 Mar 2009, 14:26
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Location: Canada
Finally, got the K-12G kit from Tube Depot. :D Thx for Joe Austin from Tube Depot.

I want to understand this kit more before build it, however, the kit's schematic drawing is not good for studying. So, I use ExpressPCB (free schematic drawing program from http://www.expresspcb.com) to redraw it. In this post, I attached these K-12G.sch file (opens with ExpressPCB), PNG image file, and PDF file.
Attachment:
K-12G.zip
Attachment:
K-12G.pdf
Attachment:
K-12G.png

Note: ExpressPCB is designed for drawing TR and IC circuit and PCB. It is not design to draw tube diagram, I use it as the drawing tool. We cannot use the sch file to translate into PCB.

For the circuit, if you can spot any improvement, please share them in this forum. Thanks.
Simon


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PostPosted: 07 May 2009, 21:19 
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Location: Winnipeg, CANADA
I would upgrade the 0.22uF caps. If you don't have any DC offset from your source, you can eliminate the input DC blocking caps, C1 and C4.

You could also increase the size power supply caps a bit.

Adding a standby switch would help prolong tube life.

I like the idea of replacing R18 with a choke, but I have not tried that.

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PostPosted: 13 May 2009, 18:03 
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Joined: 26 Oct 2008, 13:48
Posts: 70
Location: Central California coast
I recently checked on AES tubesandmore.com, they still sell the K12L. I almost went that route, and maybe should have. IMHO, A kit is the only way to go for a beginner because the risk is minimized and you are (usually) gratified quickly with good results. :wizard: Then you will have something to listen to while you fuddle around with your next diy from scratch project. :bawling:

There are several other "beginner" kits out there - both SE and PP - from a couple watts to 15 - that are worth considering. I can post URLs if anyone is interested.

Mike 8>)
If there's no sound in a vacuum, where'd the music come from? :lightbuilb:


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