Audio Research - should I replace the valves?

Probably a bit of a production from the UK, but when it is tube replacement time on my ARC amp, I ship it to them. They will give the whole thing a once over, test the tubes, and replace as necessary.  They are great to work with and don't keep it too long. And they set the bias. I realize it isn't a difficult thing to do at home, but I don't want to poke around 480V circuits unless absolutely necessary. 

Of course this means no fancy after-market tubes but just what ARC installs.

I can easily get the AR amps to Absolute Sounds, the importer in the Uk who will replace the valves but I’m told it takes a while and is expensive (anyone any experience of this?). Or I buy and replace/bias myself. But exactly what do I buy/for the Ref 110?

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!

I do agree with your suspicions, BUT I am a big fan of First saving up and paying CASH. Especially in our current economy. Secondly It should be a time to study the facts and what is worthy or MIGHT be worthy in a replacement tube. Not all tubes are made equal. You know exactly what you currently had so don't be in a rush. Save a little longer find out just a little bit more and definitely ASK MORE QUESTIONS about what you might replace those tubes with. Possibly even find someone that offers a satisfaction guarantee.

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.