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Old 10th April 2013, 05:19 PM   #1
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Default K12g Amp Question

Hey guys,

I recently built a K12G tube amp following the directions exactly. It sounds decent but it I have a couple questions.

My set up is:
-E7 Dac
-Adcom GTP-400 pre amp
-K12G 8w
-Klipsch RB61 II

1) The left two tubes glow brighter than the right tubes. Both sides are playing at the same volume and I can't really hear any differences. Is this a sign of a problem in my circuit?

2) The bass level is fine for classical music, jazz, and most rock but if I'm trying to listen to hip-hop or electronic music it falls short of my expectations (I didn't have high expectations). It almost sounds like the amp isn't touching the lower frequencies at all. Some people say that upgrading the caps will help this problem. Would you recommend this modification?

3) I'm planing to build an enclosure for the amp soon but I soldered all the parts on one side of the circuit board. I want the enclosure to show off my tubes, and I'm trying to figure out the most efficient way to do this. Can I re-solder the 9 pin connectors to the bottom of the board and attach it to the case? (essentially this would be inverting the tube).

Thanks,
Ray
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Old 10th April 2013, 05:24 PM   #2
willamp is offline willamp  United States
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I think you'll need to move all of the other components to the other side of the board. The tube sockets will need to stay on that side for the correct connections.
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Old 10th April 2013, 09:12 PM   #3
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Just getting the sockets out would be a pain. I remember someone on another forum with a K502 ( an amp similar to yours ) extending his sockets upwards off the pcb with leads - a lot of work! Swapping most of the components underneath has been done before IIRC. The bridge rectifier and small resistors could be left where they are. An insulating plate with cutouts for the ceramic sockets could be placed between the pcb and the metal chassis above preventing shorts. The volume pot could be removed from the pcb using extension wires ( dont forget the pot body earth ) as could the rca phono sockets.


Quote:
The left two tubes glow brighter than the right tubes.
Try swapping tubes around to see if the problem goes with them. Any mods done here on the heater tracks ?


Quote:
2) The bass level is fine for classical music, jazz, and most rock but if I'm trying to listen to hip-hop or electronic music it falls short of my expectations (I didn't have high expectations). It almost sounds like the amp isn't touching the lower frequencies at all. Some people say that upgrading the caps will help this problem. Would you recommend this modification.
Upgrading your output transformers will give you ( IMO ) the best bang for your buck
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Last edited by Soonerorlater; 10th April 2013 at 09:22 PM. Reason: extra detail
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Old 11th April 2013, 01:02 AM   #4
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Thanks for the replies everyone.

I switched the tubes around and the problem followed the tubes.

Does anyone have a recommendation on the Output transformer upgrade?
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Old 16th April 2014, 07:30 AM   #5
nosbor is offline nosbor  United States
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Quote:
Originally Posted by outsidesmoke View Post
I switched the tubes around and the problem followed the tubes.

Does anyone have a recommendation on the Output transformer upgrade?
The Tubes are cheap, get a second set.

I have the big edcors on my K12 build, CXPP30-MS-10K, it comes out to like $150 for the pair. Trancendar also seems to have a good reputation at their price point, but I have never heard them, same with Hammond. The tubelab guys really like Edcors, the biggest you can get for your application. Whatever traffo you go for, pay attention to the frequency response. I'm not that kind of engineer, but there seems to be a correlation between size/weight and frequency response.
Also check out voltSeconds page on the k12m, all the same updates apply. S5 Electronics K-12M Tube Amp

The B+ capacitor upgrades will net more low end extension, quite a bit more. If you only do four things to that amp, get the traffo's, do the B+ caps, replace the coupling capacitors, and remove the capacitors after the volume pot. Heater inrush sharing and the snubber caps will help stabilize the heater current. I didn't go with the auricaps, I thought they made the system sound like a titanium tweeter driven to the absolute limit, I do however like the Jantzen Silver Z in the K12. But capacitor opinion is religion and philosophy around here.

I hope you enjoy.
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Old 16th November 2014, 03:37 AM   #6
bmanh is offline bmanh  United States
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Hi all, I'm a newbie with a K12G question I'm hoping to get some help with. This thread looked like a good place for general K12G questions, so I hope this is the right place for it.

If I want to wire in a power switch and also a fuse that would both install into a chassis, how would they be wired in to the circuit? Would it require a certain gauge of wire? (or shielding)?

Many thanks!
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Old 16th November 2014, 07:29 AM   #7
nosbor is offline nosbor  United States
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I'm going to make the assumption you are using something like an IEC socket, as shown here:
Parts Express IEC Power Jack Chassis Mount

The Neutral (N pin) from the socket would just go straight to the transformer, like it does off the cable in the original kit. The Ground (G pin), would go to the chassis. The Live (L pin) would go to the fuse holder, then the switch, then the remaining wire on the transformer. For safety reasons the Live must go through the fuse and the switch, otherwise the switch could be off and you have a live wire looking to complete a circuit.

Since the original cord isn't phase aligned, one blade on the plug wider than the other, the order of hook up doesn't really matter. One wire off the cable to the transformer, the other to fuse holder, then the switch, the the transformer.

If you really want to be careful you can use a DPST, dual pole single throw, switch. Both wires from the cable go into that switch, one out goes to the transformer, the other to the fuse holder.

In my limited experience single throw switches, like a standard toggle switch, don't have pins designated as in or out. The pins are either connected or not, depending on the position of the switch. Fuse holders aren't directional either.

As far as hook up inside the chassis, I used 22 gauge silver tinned from tube depot, and that is more than enough for the short lengths of wire we use in builds. However, you MUST make sure your switch can handle the more than the 120V coming from the outlet, and the current needed by the by the circuit. An automotive toggle probably won't cut.

Happy building.
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Old 16th November 2014, 01:04 PM   #8
bmanh is offline bmanh  United States
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Thanks!

The toggle switch I'm looking to use is one I've seen on other folks DIY builds:
Toggle Switch with On/Off Label Plate : Toggle Switches | RadioShack.com

It says 3A at 125V. I'm not sure how much current the K12G pulls. Is there a way to know that from the K12G schematic?

For the fuse holder, I'm thinking of:
Screw-Cap Panel-Mount Fuse Holder : Fuse Holders | RadioShack.com

For the fuse itself, I should use something that will blow below the 3A toggle switch limit, but what would be best?

I haven't ordered the K12G kit yet, but plan to shortly, and researching all the extra stuff I'll need to do it right. I'm hoping to climb this learning curve quickly...
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Old 16th November 2014, 02:35 PM   #9
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On my 80 watts El34 amplifier I put the valves on one side (inverted the socket to the other side of the pcb) and components on the other.
This meant I could have the tubes sticking through the amplifier cover.
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Old 17th November 2014, 06:56 AM   #10
nosbor is offline nosbor  United States
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Quote:
Originally Posted by bmanh View Post
Thanks!

It says 3A at 125V. I'm not sure how much current the K12G pulls. Is there a way to know that from the K12G schematic?

For the fuse itself, I should use something that will blow below the 3A toggle switch limit, but what would be best?
Your switch and fuse holder look good.

To answer your question, yes there is a way to estimate total power draw from the schematic, but that's way beyond my ability. It can also be figured from knowing the power transformer specs.
To answer what I think you want to know, the kit comes with the appropriate fuse, just use one with the same rating for the new fuse holder. I think it's 1.5 amp, but I'd have to look to know for sure and I'm listening to that amp right now.

I would also suggest that you familiarize yourself with voltsecond's page on upgrading the K12m, but it's down at the moment...
Here is another decent write-up with most of the same mods, from that other audio forum:
S-5 Electronics K-12M Tube Amplifier Kit

The two amp's g and m, are so close the write up applies to both.
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