I would suggest making a close inspection of that monoblock's input jack integrity. But first one question: you say you've isolated the problem to the "right monoblock", which leads to me to believe that you may not have tried swapping the two mono's left for right and seeing if the problem follows that amp to the left side or not. I say this because you never know, sometimes these things can be the result of interactions between the components in question, and it still could be originating at the preamp for instance, but not manifesting itself with another model amplifier. Also, before you changed out the tubes, were any of the power tubes found to be unable to bias correctly? A bad tube could have damaged an associated resistor, which wouldn't then be ameliorated by replacing the tube. And last, try swapping (or replacing if you have spares) the output fuse, just in case one may have partially melted rather than blown. But if nothing new is revealed in doing these things, then it sounds like you're probably right in suspecting a passive part failure, though it could be something as mundane and tough to hunt down as a compromised solder joint inside.
Help: Audio Gremlins
Just today, my CJ Premier 8A right amp started making a static-like sound ( almost like a faint radio crackling) through my Maggie 3.6 tweeter. I know it is not the speaker because I swapped them, and the problem is the same. I have switched all my equip.and installed a different amp,and have positively isolated it to the right mono amp. I thought it was a bad tube, but I switched all the tubes ( both output and input) and even installed new ones to no avail. The problem MUST be with a capacitor or transformer. Have any CJ owners noticed a similar phenomenon? The amp still plays fine, and the noise does not increase with an increase in volume. Again, it sounds just like the faint crackling when a tube goes bad, but it is not the tubes. Any suggestions would be most welcome!