That's very interesting Spectron. I personally have not had to re-tube that often, in fact I have had my current tube set about two years and all still seems fine. I do agree that at certain gain levels the CAT is not dead quiet, some slight tube hiss is audible when nothing is playing. OTOH, I was amazed at the improvement that was had when I changed from the 'stock' tubes to the current NOS GE Smooth plates.
What other components are you using with the Joule and are they the same as when you had the CAT?
What other components are you using with the Joule and are they the same as when you had the CAT?