Amplifier Goes into Protect Mode Right Channel

Wanted to hear your tech thoughts on this problem. After spinning vinyl for 1-3 hours, the right channel on my solid state amplifier goes into protect mode. This repeats itself multiple times each session. I have a tube preamp and tube phono stage. Only one source - turntable. I've swapped tubes in the linestage preamp which made no difference; swapped IC cables which made no difference. The linestage tube preamp is new (one month old) but I'm beginning to think it may be a leaking cap causing the trouble. Also looking at the speaker cables as a possibility. Would that matter? Any thoughts? At the point where I'm ready to RMA the preamp for bench test. Thanks in advance.
I would suggest sequentially reversing the left and right IC connections at one end only, first between the linestage and amp, then between the phono and linestage. If the channel going into protect mode switches then the problem is something earlier in the chain than the cable you just reversed. If the problem stays in the right channel it is being caused by something later in the chain. One other possibility although less likely is an partial/intermittent short circuit in either the right speaker cable or the speaker itself. You can eliminate this possibility by reversing the speaker cable connections at the amp to see if the problem stays in the same channel or not. Good luck and let us know your findings.
Thanks for the great ideas. I'll give them a try and see what happens when I get the speaker cable back from Acoustic Zen. First, I'll hook up everything as it should be and then wait for the right channel to shut down. Unless AZ detected problems with the right speaker cable, the shutdown should happen again. Then, I'll begin the process to reverse cables as suggested above, one step at a time, to isolate the problem. I also plan to contact CODA today and see if they have any thoughts on the subject.
Was on another website and got some great ideas. Need to check out speaker damping. My speakers sit directly on carpet. They come with spikes but I didn't install them. Maybe I need to use them or put some marble pavers underneath them. Secondly, recommendation to use turntable shelf instead of placing on butcher block and then on dedicated wood table. Third idea deals with tonearm/cartridge resonance issues. If indeed it is subsonic frequency issues, this could get complicated.
You don't need to wait for your Acoustic Zen cable to come back to perform this testing. You can use Radio Shack speaker cable ($5-$10), or even some plain old lamp cord for the sake of trouble-shooting.

Why would you not install the speaker spikes??? Correct that wrong first, that should make as much of a difference as isolating your turntable. If the issue is feedback going through your system, fix the spike issue first, then if there is still excessive woofer excursion, look into a turntable wall mount.

If you are still having issues, then follow the switching cables path suggested above to trace down the guilty component.
Have had this problem before, with MIT SC and classe amp, would send the amp into oscillation, never figured out, MIT checked the cable and was stumped, the cable and amp would not match up. That was the solve, no other cable caused the problem.

Make sure your rca's to your amp if single ended....are installed properly, ie, tightened so the ground is making good contact. Had this problem with WBT's once and it always happened when the system had been playing and heated up. Pliers fixed that problem, a barrel on one cable was a little too big for the inputs.

Did you find out if your tube preamp was passing DC? Could also be a loose solder joint around the tube socket from swapping out tubes.....have had that happen also.

Double check cartridge clips and wire/solder connection to the clips - has not broken or been compromised....have had that happen also and ended up sending my phono pre back only to find out it was fine....

Stay in this hobby long enough and just about everything will happen will find it, good luck!