Send in the amp first.
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The sound you describe is something I have come to associate with Tesla E 34L power output tubes.
Although I like Tesla's, if your CJ uses EL34's and the factory choose that tube, I would look to that as a possible source of noise. One amplifier that had this identical problem "repaired itself" after additional hours of burn in and re-biassing the circuit.
Very strange indeed. I would go back and hook up each C-J component to each Bryston component again, and run them that way for a few days to see if the problem eventually crops up when the PV-5 and MV-50 are isolated from one another or not. (About AP's suggestion, I am pretty sure C-J is using Sovtek/E-H EL-34's; I take it that your output tubes are biasing properly?) If the problem never shows up when using these in combination with the SS components, but comes back as soon as you reconnect the C-J's, then you might want to try subbing out some spare tubes (if you have them) in the preamp's line stage sockets (the fact that the problem apppears in both channels makes it unlikely that this a faulty tube problem in the amp).
I want to thank everybody for the suggestions to help me with the loud hissing problem. Today, I began to play with tubes in both amps. I readjusted the bias on power amp, removed and reinstalled all of the tubes. Then I began substituting a NOS RCA 5751 in the line stage of PV5 preamp. One of the 5751's was very "noisy", causing the hissing sound. I bought this preamp in February and never replaced any tubes, until today. I still wonder why the hiss disappeared when connected to Bryston 3B-ST power amp? Thanks again, Pete.
It could have just been an intermitent problem that didn't show up the first time you connected the C-J pre to the Bryston, or the different input load seen by the cathode follower tube when swapping amps could, I suppose, have caused it to behave a little differently. Welcome to the wonderful world of preamp tubes, separating the merely committed from the truly insane!