Do I need new tubes?

That's not really a symptom of a tube going bad and it's not unusual for tubes to take some time to warmup. But if you have some spares drop them in and see what happens. BTW always always have a full retube for your system on hand!

That is an odd symptom. I'll second @jond 's  recommendation to put in the spare set of tubes... it'll take 10 to 20 hours for the new tubes to sound right. 

You can never have enough tubes!!

Hoping to piggyback on this discussion, maybe change the header to "DID I need new tubes?"

  Recently had my RM-9 Music Reference amp repaired, rather extensively, at George Meyer Audio in L.A. after losing the left channel. I'd been running 4 KT-120's, for several years. 

  I was told to replace the tubes, because they "had no gain."  I had swapped the tubes, and all other inputs, extensively trying to identify the possible cause of the left channel outage, and each tube glowed, produced output, and responded to volume control on the right channel.  

   Further, I was told not to use those 120's or I'd be bringing the amp back for repair again. He was not very instructive when I tried to ask him about all this.  

   So, did I need new tubes?  Which I've ordered by the way.  

Appreciate any input and feedback.  thanks.

Jeff