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Hello. I have a few questions about my amp that I hope you can answer. It is a 40 watt sunn solarus 212 combo (open back). I know it is supposed to have el34's in it, but someone has put groove tube 6ca7's in it. I know the 6ca7 is compatible, but I really don't know anything else about them. It sounds great and starts to break up around 5...but in addition to breaking up the sound gets super muddy. Could this be the 6ca7's? Or could it be the speakers? It still has the original sunn transducers, so I'm sure those need replaced anyway. Any recommendations as to which speakers to use? Or which tubes I should get? I use a ton of pedals if that makes a difference, and I mainly use single coil guitars (jaguar, dipinto galaxie 4, strat). Thank you for your infinite knowledge and guidance. It is much appreciated.

I can't answer your question with any degree of certainty because I don't have a lot of experience with that line of amps. For all I know, this might be an inherent characteristic to it.
One thing I can tell you is that in my experience, 6CA7s sound very EL34-like... They're practically indistinguishable to my ears. So I doubt the problem is related to the nature of 6CA7s.

You might have weakening power tubes or a bias problem but from what you're saying, it seems equally likely that you may have a bad speaker(s)

The cheapest way for you to rule either out would be to run the amp into an other cab and see if the problem persists.