Audio Research - should I replace the valves?

Typically tubes slowly deteriorate… exactly as you describe. I would replace them and keep your existing ones as backups. I always have a set of backups anyway.

I always try and buy my repacements from Audio Research… both because they extensively test them and to help support a great company. But you can save money by buying from The Tube Store, Upscale Audio, or other. Make sure you get matched sets. Most of these places sells “replacement” sets for specific components.

I have all tube gear… all ARC for my main system. See my UserID.

Thanks! I didn't realise they deteriorate - i thought the just blew!

Presumably I can't put them in myself as they need biasing (whatever that is!)?

You should learn how to replace and bias the tubes. This information is in the service manual!

Output Tube Bias Adjustment As shipped from the factory, the output “bias” adjustments are set for a nominal 65mA per 6550 tube. Under these idle conditions the tubes are each dissipating approximately 27 watts of their 48 watt rating (42 watt plate, 6 watt screen). This point of operation provides “enriched” Class AB1, and will satisfy the most critical listener. For best results, operate and adjust the Reference110 at 120VAC. Adjustment must be made under zero-signal conditions after at least 15-20 minutes of uninterrupted stabilization time. A digital voltmeter capable of accurate measurements with 0.lmVDC resolution is preferred for accurate adjustment (must have 31/2 digit display). Use the plastic alignment tool provided to make the adjustment. The measurement points are yellow and black banana test jacks next to each output tube. Adjust the “bias” for a voltage reading of 65mVDC (.065 Volt DC) at the blue bias pot for one of each output tube pair as follows, noting the voltage setting of the larger V number tube in each pair is slaved to the adjustment setting of its lower V number companion tube: Adjust V5 for 65mVDC and measure its companion tube V7 to verify a reading of 57 to 73mVDC. Repeat procedure by adjusting and measuring V9 to read 65mVDC and verify V11 reads 57-73mVDC; adjust and measure V6 to read 65mVDC and verify V8 reads 57-73mVDC, and finally adjust and measure V10 to read 65mVDC and verify that V12 reads 57-73 mVDC

Replace older still operating tubes and use them as spares. 

i don’t think they sounds as good as they did but no pops or whistles or any other strange noises etc - just a bit flat sounding.

This is a good cause to replace. Problem with too many tubes is you cannot tell for sure which one or ones reached end of life.

Normally power tubes wear out faster, a starting point to order a new set from ARC, with preamp ones to follow.

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!)

Yes, you seat the tubes and then bias. As a long term ARC owner, trust me please and invest in a decent Fluke. As in Fluke meter. And don't sweat it. Except that finding a reliable source of tubes particularly for your amp is not so easy anymore. 

Tube replacement is simple. Do not touch the tubes with your fingers… use a clean cloth. Biasing is easy… here is a copy of the manual in case you don’t know where it is.

Do this once and you’ll be a pro. It sounds much harder than is.

Fluke meters are good and come in vastly different cost ranges. You do not need to spend a lot. I always have a multimeter around, there are hundreds of brands. 

https://audioresearch.com/wp-content/uploads/2021/06/REF110_Manual.pdf

Thanks, I do have a Fluke. I’m going to use KT120 valves in my 110. Is it the same settings? I looked at the manual and it says you should use 120v AC to adjust the bias. Obviously in the UK we have 240v AC or am I being dim?

240v in UK is fine. What they mean is the wall voltage should be at 120/240VAC as the preferred voltage to set bias. This is because the internal amplifier voltage varies if the wall voltage varies. 

So my preamp used 6922’s and they should last about 5,000 - 10,000 hours, but most power tubes should be replaced every 2000  - 2500 hours. 

Real NOS tubes last longer than the current Russian or Chinese production. If you want current production, maybe you could buy Sophia Electric KT88 big bottle. They are better sounding than any KT120.

should I replace the valves?

yes... as many other experienced hands here have said...

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.

if u want NOS, try the top 3 dealers: jim mcshane, brent jessee or andy at vintage tube services unless u need new stock. jim carries a good bit of new stock, but i dont know if he carries what ur usin.

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.

@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. 

hey there @immatthewj thanks for catchin that so quick!

i just re-read my emails and revisited the website. im mistaken.

seems even tho theyre sellin tubes again they never took down their "we paused out tube selling" page. 

thank you my friend

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. 

"

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. "

@immatthewj holy smoke i heard about new production longetivity issues, but man that sucks. i gotta say ive had no such problems, but i hear aout em plenty. been runnin new production tubes not-so-gently in my guitar amps for a long time with very few surprises, tho i think thats in the power section. funny i never paid no mind to tube selection til i started getting into hifi. always told my tech, hey, whatever makes it sound good. and it always sounded good.

also, both jim and kevin are known for testing the heck outta them. andy, i think, puts em thru the ringer as well, tho he doesnt do new production.  

@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). 

OP. As you are in the UK, Watford Valves have a good stock of 6550s for your power amp.

It looks like Tubeamp doctor in Germany has 6H30s - for your pre and driver valves in your power amps.

The latter are not massively common and are Russian, so harder to come by and likely to get even harder to come by over time.

@immatthewj  i hear u brother!