Herron VTPH-2A ... tube dying?

Today I noticed some strange high frequency ringing, very faint, and narrowed it down to the left channel on my VTPH-2A ... it subsequently just lost most of its output on that channel only. I am assuming (hoping) its just a tube failing? Curious now if I replace, is it best to do in pairs? And if I were to try rolling a couple options, what are a some tubes fellow Herron owners enjoy in the VTPH-2A aside from the stock? I listen to a lot much different music from ambient to jazz and fusion to disco and house, so I can't really narrow it down to much, but definitely not much loud rock with distorted guitars etc.

SP-10MK3 > FR-66s with Zu DL103 / FR-64s with Grace F9/US14 > VTPH2A 
I have yet to hear of someone doing better than Keith. He tests and throws away more than he uses. But yet he doesn't really charge for this. I would just call him and get another set. His tested matched sets are awfully hard to beat.
I retubed my Herron using Sovtek 12AXLPS and 12AT7 (which I can't recall) but I did email Jim McShane. He has a great handle on phono tubes. 
I use NOS Telefunkens in my VTPH-2a not a cheap option but better than any new issue tubes you can buy.

for the love of ____ do yourself a favor and buy this


go from there with knowledge, you will have it for the rest of your life

this one, or another: always get the instruction book (it has it)

I have it and it’s little brother model 157. compact, easy, take it to friends homes ...