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Please Help Me Trouble Shoot My K-12G
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Author:  JimOfOakCreek [ 23 Jan 2011, 11:46 ]
Post subject:  Please Help Me Trouble Shoot My K-12G

I've spent the weekend transfering my K12G into a wooden enclosure. The top of the board is mounted to the bottom of the wooden enclosure. I did use the same stand-offs.

I thought all was going well but I've lost sound. :bawling:

Symptoms: When I turn on the amp the tubes light up. I can hear an extremely extremely faint hum coming from each speaker if I put my ear less than an inch away from the speaker. There is life!

What I did: I unsoldered all capacitors and moved them to the bottom of the board. I removed the volume control, destroying it in the process. I removed the inputs. I added an additional input, 2 total to the enclosure. I had to add extension wires to all the transformers. I completely removed the DC blocking caps and replaced them with 16 gauge solid wire. I added a Radio Shack volume control temporarily until my ALPS VC gets delivered.

Questions: I used a common ground for the inputs. I am assuming the inputs do not need the ground separated in each instance. I removed the RS volume control and conected the input wire directly to the output wire still with no sound.

Other than that I am clueless as to why there is no sound. Anyone care to take a shot at trouble shooting? :confused:

Author:  Generic1964 [ 23 Jan 2011, 15:32 ]
Post subject:  Re: Please Help Me Trouble Shoot My K-12G

When you say that you destroyed the volume pot in the process of removing I'm gonna guess that you didn't use solder wick and instead "teeter-tottered" it out while cooking the solder joints. Perhaps, in the process, you cracked a track on the circuit board.?

Time for some good light and a magnifying glass so you can take a real close look at that area. This is a double-sided board so it's possible that in moving componants from one side to the other you ripped a couple of the feedthroughs out with the pot or some other componant. Eyeball EVERYTHING closely.

Did you move the bridge recifier to the bottom side of the board? If so then you're plussin' when you ought to be minusin' ;-)

Since you removed the input RCAs then I'll assume you used shielded wire to your panel jacks. Look closely and make sure you didn't have a stray strand of shield braid shorting to the hot.

Take a systematic approach: start at your inputs and work your way through to the speakers and power supply. Or vise-versa...

That's all i've got. Good luck and keep us posted!

Peace,

-Generic1964

Author:  JimOfOakCreek [ 23 Jan 2011, 18:59 ]
Post subject:  Re: Please Help Me Trouble Shoot My K-12G

The bridge rectifier has been replaced with 4 diodes which worked fine before the move. I left those as is when I made the move so that's not the problem.

I dont see any breaks in the trace.

Could I have a bad tube?

Author:  Generic1964 [ 23 Jan 2011, 22:29 ]
Post subject:  Re: Please Help Me Trouble Shoot My K-12G

A bad tube is always possible but since this failure coincided with your modifications it's not likely. Since both channels are out the problem is something common to both.

Have you checked and double-checked your work in a systematic fashion?

Do you have a volt/ohm meter? I'm a total noob with tubes but I can take some voltage measurements for you to compare to if need be.

I'd be willing to bet that if you sleep on it, step away from it, and take a fresh look at it tomorrow you'll find an obvious error in your modification process.

Discharge all caps before ya stick your nose in there looking for the broken trace or lifted pad...

Be safe and good luck.

Keep us posted.

-Generic1964

Author:  Gio [ 24 Jan 2011, 17:09 ]
Post subject:  Re: Please Help Me Trouble Shoot My K-12G

Hi Jim,

The problem seems to be around the signal so check take a good long look for a mis-connection. Pay close attention to the output transformer connections, the rca connections and the potentiometer. You may have reversed something. Also check polarity of the caps, but if those had been wrong you likely would have already known about it.

Cheers

Author:  JimOfOakCreek [ 24 Jan 2011, 18:40 ]
Post subject:  Re: Please Help Me Trouble Shoot My K-12G

I checked the continuity between the inputs and the tube pins that are fed from the volume pot. When I adjust the volume I can observe the resistance change at the tube pin. I would gather that is an indiction of correct wiring.

I'll find the problem, just a matter of time.

I am preparing to leave the country for a couple of weeks so this may have to wait until my return.

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