My Tubed Amps Entered "Twilight Zone"

Last week, My Conrad-Johnson tubed PV5 preamp and MV50 power amp started to emit a loud hissing sound through both speakers about 10 seconds after turning on. So loud, that I had to shut them down. I checked all the tubes and they all were lighting up. MV50 was re-tubed 2 months ago by CJ. I then hooked up the PV5 to my Bryston 3B-ST power amp. The sound was perfect, with no hiss at all. I then tried my Bryston B-60P integrated as a preamp with the CJ MV50 power amp. No hiss and the sound was great. I re-connected the PV5 to the MV50 and used different interconnects and the loud hiss returned. Very frustrating experience. I called CJ service department. Knut suggested that one or both power supplies of the PV5 or MV50 needs replaced. If the power supplies are bad, why do they play well with the Bryston SS amps? The loud hissing occours only when the CJ equipment is used together? Any suggestions of what is going on here? Thanks, Pete.