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Old 10th April 2013, 04:19 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, 04:24 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, 08:12 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 08:22 PM. Reason: extra detail
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Old 11th April 2013, 12:02 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, 06:30 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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