Audio Research - should I replace the valves?

@ghdprentice upscale audio quite ("paused") sellin tubes this past april. 

@cey  , when was the last time you checked?  Uncle Kevin has been selling tubes again for a while now. 

Thanks all. Not sure whether biasing the valves is beyond my skills but will have a read. Stupid question but assume you fit them and then do the bias? (Told you I might not be up to the job!)

Could be that the bias has gotten way low & just biasing them will make a big improvement?

Regardless, if/when you do put in new tubes, you will DEFINITELY need to check & set the bias before using.  Whenever I replace output tubes I always back the bias off all the way before turning the amp on and then I go from there.

I've owned and steadily enjoyed a McIntosh MC275 tube amp and C2600 tube preamp since late 2017.  I've never tried to estimate the cumulative hrs. of listening, but it's up there.  I purchased a complete replacement set of replacement tubes for both components from McIntosh a couple of years ago, and stored them away for eventual replacement. I don't recall seeing any bias adjustments and frankly didn't know it was a thing.  I suppose it's time to swap them out!

@rickisme  , I just did a cursory search & I am picking up that the newer 275s are self biasing.  Other wise, occasional checking & adjusting the bias of output tubes is a MUST.  Especially after installing a new set.  Your owners manual should clarify that for you.

No sweat, @cey  .

anyway, the last time I bought output tubes was a couple of years ago; I bought a dozen of the reissued Tungsol EL34s from Jim McShane to replace a dozen of the reissued Mullards that I bought from Uncle Kevin that didn't last very long.

I am a big fan of Jim McShane now. 

@cey  , well, it took Jim a lot longer to get a batch of 12 together than it did Uncle Kevin, and once Jim took payment he would email me ever so often to let me know what stage he was in in the process of burning them in & testing.  Which is not to say that Uncle Kevin didn't have hordes of tubes burned in & tested with their numbers already established to choose from.  And, I did run those reissues from Uncle Kevin a lot harder than I run the tubes I bought from Jim (just the mood swing period I was in & presently am in).