Should I upgrade my Tubes

Did you re-bias the KT120 tubes?  In my Cronus Magnum 1, the factory supplied KT120 tubes had 3 years on them and I played the amp every single day.  They still sounded great.  Check the 4 fuses where you bias the tubes.  1 or more may be blown. If that isn’t the case, check the preamp tube, it may be dead. 

Rodman Gave very sensible advice

GL KT77s are great tubes, although currently I'm using a pair (I have a quad of these) of unused Sovtek KT88s I've had for a while...somehow they sound great.

@decooney - Never did try anything with less potential power than the KT88/6550, being an SPL lover and trying to squeeze as much as possible, with the lowest distortion, from my modded SLM-100s.      A relatively small, highly treated room with 93dB/2.83V speakers (w/active biamping and SS, below 80Hz, 60dB/oct) helps, but.....                                            The best presentation I’ve had, was provided by the GEs.     Glad I never owned an octet of the original Genelex or Tung-Sols.      I’d have probably been ruined for life.      Would have been nice, had the GL KT77 been available when I was modding/updating ST-70s.

I fixed it, my bad. I am totally digital streaming and I have a Codex which I guess I accidentally put in Preamp mode. Changed the setting and everything worked. Cost me 2 days of lost pleasure though.

I may punish myself (sic) by spending $ on another set of power tubes (as a back up) and enter the world of tube rolling. Any solid suggestions for listening to blues guitar, jazz and chicks singing ?

Also, do I need to be concerned about the 5 preamp tubes ?