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PostPosted: 13 May 2009, 21:44 
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Hi Mike,
Feel free to start up a new thread and post the links.
Cheers

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PostPosted: 22 Sep 2009, 04:29 
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Hello All,
This thread is as close to what I am thinking about for a project as I can find. I have built a K-502 amp from tubesandmore and I have all the parts I need to build another one from scratch without the pcb. The pcb is a bit fragile. I have been wanting to do this for some time, but can't get it through my head how to lay out the wiring of the components. I built a P1 from scratch from AX84.com and it turned out nice. Those guys have everything figured out for you. Their projects are well documented. While the turret board layout shown here for the K-12M is nice, I really would like to do this point to point like my Bottlehead Seduction. I get a little dislexic trying to invision how to lay the wiring out from a schematic.

Has anyone attempted to wire a K-502, K-12M, K-12G up this way? I have a nice new Edcor power tranny and two Hammond 1609s that would look nice together and hopefully sound better than the stock transformers. I would like to set it up with the Edcor right in the middle between the two Hammonds. I have seen amps like that. Can anyone get me started with some suggestions?

Thanks,
fewjr


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PostPosted: 22 Sep 2009, 19:58 
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Don't know how to advise you here, other than to pull out lots of paper and start drawing, as I did. But then, I had the PCB as a reference which helped get things started. I used turrets, since they let me attach several bits to one post (and de-attache them when necessary.). But they do cost $0.19 each, so PTP is cheaper.

Frankly, it was a frustrating process to design the board the way I did, but I think I learned something along the way...I'm not sure exactly what I learned, other than to be brave! Good luck!

Oh, and some fine gentleman contacted me way back wanting to purchase the PCB from my kit. By the time I found the PCB in my very messy shop I had lost the contact information, so please try again, if you're still interested.


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PostPosted: 11 Oct 2009, 21:39 
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Gio,
You mentioned using a choke in the power supply. I was wondering what value you would reccomend? I have some laying around....a 2.5H and a 1.75 from a Dynaco. I have a few others but I think these two are the only ones that might even fit the bill. You suggestions here are desired.

I was wondering if it would be possible to make a CCS for the power section out of an LM317 regulator. I have used this in the Oddblocks once before but it is certainly a different application. Any idea on where the idle current sits on the 10GV8? I was wondering if it would be possible to sub the LM317 for the 150R shared cathode resistor on the 10GV8. I am not yet saavy enough to figure this out (if even possible) on my own yet.

I recently built the K-502 and had great results. I happen to have all of the parts to put together a K-12G. I will be doing this point-to-point with a turre board. My power trafo is an Edcor rated at 180V (which is what I understand is the voltage of the K-12G) and OPTs salvaged from an Eico HF-81 (8K with 4,8,16 sec).

I want to try a CCS much like Voltseconds but as I was studying it I rebembered Bruce's Oddblocks and the LM317. Why couldn't this be used here? It is so simple, just set the current with the resistor.....if in fact that is all that I am doing.

Can somebody help me work this out? Or am I just too nieve at this point in my DIY journey?

Thanks!
Jeff Miller
millerjeff@ccmhonline.com :confused:


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PostPosted: 12 Oct 2009, 11:18 
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Hi Jeff, adding a choke is pretty simple. Replace a resistor in the power supply filter with a choke of similar resistance and large enough to handle the current. About 5 - 15H would do.

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PostPosted: 13 Oct 2009, 13:23 
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Hi Jeff, For all you folks in diy land, I answered this in detail to Jeff earlier by PM, I am putting an overview here as there is probably more of you with similar thoughts.

Yes the LM317 regulator will work in the K-12. So depending on what tubes you actually have, I would set the LM317 for 80 ma (a 15 ohm resistor will do this). I have studied the Volt Second modifications and used some in my original K-12. Fine stuff. I did do a k-12 with a LM317 and it worked fine, I just didn't have the test gear then that I do now and don't know how well. I unfortunately scrapped it for parts a long time ago. The balance pot should be close to 25 ohms, up to 50 is likely OK in K-12 because of the minimal idle current. Going above this level will tend to interfere with the bias on the cathodes (because of the voltage drop in the pot). The CCS requires a minimum of 4 volts to operate correctly. Very odd things occur when you go below that level. All of which translate into massive distortion.

Good listening
Bruce

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PostPosted: 13 Dec 2009, 01:50 
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Hello, everyone. Been busy with a thing or twelve. Anyway, I finally got around to setting up my K-12G amp with proper speakers (and DVD player for CDs) in my home office. Alas, it is not an ideal listening space as the speakers are not located in a way that output is balanced. In the original build, I used a Radio Shack dual control volume pot (100K audio). The output was strange...no sound until the knob was at about 10 o'clock and too much volume at 12 o'clock. Plus, no way to balance sound between speakers. So I ordered 100K linear taper pots and installed one for each channel. The results are just fine.: good precision on volume adjustment for each channel. But now there are two klnobs to play with to get the volume right.

Where to go next? Single volume control with a balance control pot, or stay put with what I have? Opinions are welcome! Lofton


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PostPosted: 13 Dec 2009, 11:21 
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Hi Lofton,

Did you ground the pot? Note that there is a location on the PCB right next to the input that grounds the enclosure of the pot.

If what you have is working fine and you don't mind dual-mono pots, I would stick with that.

Cheers

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PostPosted: 13 Dec 2009, 11:34 
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Thank you, Gio! Yes, I did ground the pots. As you may recall, for this build I created a turret board and didn't use the PCB.

The bass response isn't great so maybe I could investigate different OTs. Then again, not much of what I listen to in my office has much low end...

Now that I've been listening to the amp for a few days I find the dual mono pot arrangement works just fine. And it makes me feel ever so little bit like a sound engineer while I tweak the volume on the two channels. (I'm reflecting on the scenes in the movie "Once" of the recording studio with hundreds of sliding pots on the sound board.)
Cheers,
Lofton


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PostPosted: 14 Dec 2009, 22:31 
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My K-12M was pretty good, about -1dB at 20Hz and -2dB at 20kHz. But better iron is always good. ;)

Post a pic of your amp.

Cheers

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