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PostPosted: 19 Aug 2010, 21:40 
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Joined: 18 Feb 2010, 05:14
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Location: Incheon, South Korea
gofar99 wrote:
Hi, Sorry, I've been a bit tardy with looking at the forum this month. In answer to an earlier question -Sierra Vista, Bisbee is just over the hill. PM me if you want to chat about old or future times.

I always like to give credit when due, and the S-5 Electronics K-12 tube amp kit is a great starter project and fun to tinker with. It has always been short in the bass area, but rather nice in the mids and top range. As a basic kit the price is right. Again welcome to diy audio.

Wow, another Cochise County guy. I can't count how many times I've been between Bisbee, SV, Tombstone and Tucson. I could make the drive in my sleep... I think I have. I don't think I'll be back through AZ until maybe next spring, you can count on me dropping you a line.

I agree, the K12g was a great start, and the mids and highs sound nice. If I had it to do over again, I probably wouldn't do it any differently. That first night, after I fired it up and nothing exploded, was a real eye-opener (first time hearing a tube amp). I stayed up late going through as much of my mp3 library as I could, just to see how they sounded. I've recently had to take mine down due to excessive hum. I upgraded the PS recently, and while it made an improvement in terms of some of the "flabby" bass, I think I did a poor job with routing power wires and shielding etc. I've abused that circuit board quite a bit with different changes and upgrades, and it's getting a little tired. At this point, I'll either rebuild the whole thing point to point, order a new K12g kit and start fresh (maybe tube rectified, CCS?) or use the trannies for another project.

In the meantime, I'm working on a SE KT88 with a 6SN7 driver stage. I'll eventually put KT120s into it, but I'm going to get it started with KT88s. I'll start a separate thread later.
connemaraguitars wrote:
Please let us know how the CAD program works.

So far I am very pleased with SE Amp CAD. I just started building the amp, so I can't comment on accuracy or viability, but I found it to be very useful, and helped me clear up some things in my head regarding how certain variables affect others. Before it arrived in the mail, I started playing around with drawing my own load-lines and doing it by hand, and even modeling the KT-120s from the datasheets as best I could in an Excel datasheet/graph. SE Amp CAD took all the leg-work out. The downside being that their tube library is limited to what they've modeled and put in themselves (though the tube library covers quite a few common tubes). I would definitely check it out. I got the package, SE Amp CAD and Amp CAD together, from Antique Electronic Supply. Amp CAD isn't quite as specialized, but I still found it very useful in planning my drive stage.

Again, I haven't finished the amp, so I can't backup the programs real-world usefulness, but it's gotten some pretty good reviews from others.

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PostPosted: 20 Aug 2010, 02:29 
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"In the meantime, I'm working on a SE KT88 with a 6SN7 driver stage. I'll eventually put KT120s into it, but I'm going to get it started with KT88s. I'll start a separate thread later. "

I built a SE 6SN7/KT120 amp. Very impressing and pushed out a lot of power.

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PostPosted: 20 Aug 2010, 10:49 
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Cold Macaroni wrote:
Wow, another Cochise County guy. I can't count how many times I've been between Bisbee, SV, Tombstone and Tucson. I could make the drive in my sleep... I think I have. I don't think I'll be back through AZ until maybe next spring, you can count on me dropping you a line.

Hi, Look me up when you get here.

Good Listening
Bruce

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PostPosted: 08 Sep 2010, 16:40 
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Joined: 23 Jul 2010, 18:23
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OK, you will know how new I am to all of this.

I just bought a K12 kit. I want to mount the finished product through an enclosures so that only the tubes and transformers are on the top side of the PCB so everything else will be mounted underneath. I saw pictures on this site where one builder mounted the potentiometer on the underneath side of the printed board. Does mounting the pot on the under side of the board create problems? 4 of the 6 pins will not be in the same holes as when it is mounted on the printed side of the board.

Thanks -- Chuck


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PostPosted: 08 Sep 2010, 18:37 
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Hi Chuck, welcome to the forum.

Easiest is to mount the tubes from the top as intended. The diode bridge will also have to mount from the top to maintain the proper connections. All the resistors and capacitor can mount from the underside. Just be sure that the polarity is correct for the electrolytic capacitors so double and triple check.

As for the potentiometer, I suggest you don't mount it directly to the board. If you use short wires it will be easier to complete the chassis and if in the future you would like to upgrade the pot or you have to change it because it goes bad or noisy you don't have to worry about everything lining up. :2c:
Cheers

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[ DIY Mains AC Power Cable Cord ] - [ Gobo LM1875 Amp Kit ] - [ Tang Band D4-1 Horn Speaker Kit ] - [ Monoblock Push-Pull KT88 Tube Amp Kit ]


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PostPosted: 08 Sep 2010, 19:10 
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Joined: 23 Jul 2010, 18:23
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Thanks for the advice. I have the board partially completed as you have outlined. I stopped at the pot because: first, I was unsure that if I added short wires as you advise, it might introduce hum, etc and second, I wasn't sure whether the 6 pins had to be oriented as if mounted on top.

Thanks for the answers. So far, I have burned myself or the dog. Have some cuts from the sheetmetal work.

I'm anxious to see if it works the first time it is fired up? I have checked continuity with each set of soldering I have done.

-- Chuck


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PostPosted: 10 Sep 2010, 22:34 
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Joined: 03 Jan 2009, 10:44
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Adding wires won't create problems. Just try to keep them as short as possible but don't get too picky on this. My PTP build of this amp had lots of extra wire and it's really quiet.

Rather than a volume pot I'd strongly suggest a Lightspeed Attenuator, described elsewhere on this forum. You can source parts from Uriah and build it in under an hour. I've done this and am really happy with the results. In the future I plan to incorporate this component into all my amps.


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PostPosted: 11 Sep 2010, 11:03 
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I'll second a Lightspeed Attenuator / Optocoupler Passive Attenuator for the volume control. They are fantastic.
Let us know how you make out with your K-12G build.
Cheers

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[ DIY Mains AC Power Cable Cord ] - [ Gobo LM1875 Amp Kit ] - [ Tang Band D4-1 Horn Speaker Kit ] - [ Monoblock Push-Pull KT88 Tube Amp Kit ]


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PostPosted: 18 Sep 2010, 19:24 
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Joined: 23 Jul 2010, 18:23
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Well, the more I read, the more stuff I thought about adding. However, I became impatient and finally put it all together (S5 K12). It worked the first time! I am shocked. The only electronic experience I had was splicing wires for automotive purposes. I had even located a guy a few miles from here that works on tube amplifiers figuring I would have to have him correct what I had put together.

I set the amp on the cement patio (anticipating an explosion); plugged an extension cord into a GFI outlet. No explosion, just music after a second or two.

Sounds good. I had substituted larger caps, VoltSecond, etc per the several posts here.

The amp has very little hum. In fact, the hum doesn't sound like its coming through the speakers; I can hear it when I put my ear close to the amp itself. The does seem to be some sibilance. I have the amp hooked up to two 6" Audio Nirvana speakers. They are terrific sounding speakers - Supposed to be fairly efficient - somewhere around 96db.

I run my Cowan S9 in at half volume; amp set at about half volume and there is plenty of sound for high normal listening (that doesn't mean I am high when I am listening).

Never would have attempted this without the help from this site. I didn't think there was really much chance in my case of killing myself, however, as my wife has told me for years that I am heartless.

Thanks everyone who has posted here.

--Chuck


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PostPosted: 18 Sep 2010, 22:00 
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Joined: 23 Jul 2010, 18:23
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Here is a pic of the result


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