one channel crackling [solved]

[Karl5150]

I installed the c4s board and the #s are all good. Hooked it up and it is definitely an upgrade, more on that later.
In between tracks I noticed it started crackling from the left channel. I swapped the tubes and it remained in the left channel. Back on the bench I found that 13L had never been soldered and what must have previously been a good mechanical connection at 13L was loose. Soldered it and back to the system.
Unfortunately that wasn't it. I've checked other chassis grounds and they all read as low as touching the 2 volt meter probes together. (00.2 on the 200 ohm setting)  It had been dead quiet before.
A little expert advice would be appreciated, thanks in advance,
Karl

[Doc B.]

Keep looking for other bad solder joints.

[Karl5150]

Doc,
Out to the bench for a visual, re-flowed 22 & 23 just in case. Both channels are now scratchy, almost continuous at first then tapering off to the point of silence for 2-30 seconds then one side, the other, both volume independent of the volume pot setting. Totally random, which side (or both) and the duration of either the noise or the silence in between. Swapped tubes with spares and no change.
Left it running for the better part of an hour and silence dominates with only intermittent noise. It would definitely be termed crackling in character, of varying volume and independent of source, program sound is clear and accurate with the noise layered on to it.     

[Paul Birkeland]

Both channels are now scratchy

This narrows things down to the 6V power supply (back of the transformer where the big black diodes are), or the high voltage supply (including grounds).

There's very likely still a bad solder joint or two somewhere that have been aggravated by the physical movement of parts involved in the upgrade.

[Karl5150]

You guys must never tire of being right, or making fine products. Thank you on both counts. I found the cold joint.
Obvious from the start was the fact that C4S is quite an upgrade.
If I can describe the sound listening with eyes closed in terms of a visual experience: The original set-up was like a well rendered photo of very limited height compared to width, containing great detail but shot with an f-stop allowing only an extremely short depth of field. Once installed it became more like the display from a high-end sat.nav. system. You get a feel for the music in space, in a true 3 dimensional sense.
I think I will enjoy it for a little while before seeing where the integration upgrade takes it.
Thanks again.