Power supply / Grid crackling

[plexi50]

I have a Dean markley CD120 here that is crackling in the phase inverter feeding the grid and the power tubes. This is with the preamp tubes pulled. I have replaced all the resistors in the phase inverter section along with the coupling caps and all 1.5 grid resistors on each power tube. This has really got me stumped. I have repaired many amplifiers with fractured phase inverter coupling cap resistors. I've done everything in my power in my knowledge to figure this one out and it is not conforming. Any tips would be greatly appreciated! Video link here. https://m.facebook.com/story.php?story_fbid=2956228494465400&id=100002348347549

[SILVERGUN]

I had crackling in that area caused by a failing snubber cap across the PI plates. Not sure if yours has one...
After listening to the video on my phone Im not sure thats not some RF leaking in.

[plexi50]

Yes I replaced everything including the snubber 47pf cap. I mean I'm wondering if the output transformer might be going south that may be a possibility but I've never seen it.

[SILVERGUN]

Id suspect a filter cap before the OT, but Im just a welding machine troubleshooter.
Caps fail way more often than transformers in either application.

[DummyLoad]

that sounds like tube or plate resistor arcing from breakdown.


--pete

[shooter]

fwiw;

I had 2 amps that the OT ohmed ok, even seemed ok at idle, once I put a signal in one side started wonking out.  eventually I'd get internal arc's on 1 tube, swapping the OT primaries the "other" tube started arcing.  the arcing could only be seen in a dark room, it did crackle.

look close at the sockets also, had a couple that had "corroded" cups, real bright light found them

[plexi50]

I will take another look at the tube sockets in the soldering and see if there's anything I've missed.. the plate resistors coupling caps and grid resistors are the first things I changed. I pulled the pi tube and now the amp is crackling even with the pi tube pulled. 

[shooter]

there's still socket, pa tubes, OT, speakers n jacks for the easy list
harder might be conductive boards, finiky PS caps n R's, thermal stuff, troubleshooting is like and endless version of hunting Easter eggs 

[mwelch55]

I had a crate blue voodoo 50W amp that was making random crackling noises.  To make a long story short, I replaced the OT and that fixed it.  The OT must have been arcing inside.