Audio Research Tube AMP Reliability

I noticed that the ARC amps have high idle current, it looks to be about 4 times the amp rated power output.

I think that this indicates that the amp runs in single ended class A. Is that why people tend to like the sound? A Pass Labs XA amp also runs in single ended class A.

Has anyone ever compared a Pass XA 30.5 against something like a VT 50 from ARC to see if they have a similar sound?

I am surprised this blog even exists. The last time there was a serious discussion of the reliability of ARC tube amps, the postings were removed in less than two weeks, no doubt due to pressure from the manufacturer. I'll try to capture some of my previous remarks here and hope that it survives. First, let me say that I don't think reliability with tubes is a problem with anyone's pre-amps, including ARC. I own a Ref 3a and it is a joy to listen to and a delight to own. But high-powered tube amps can be problematic regardless of manufacturer. Someone said it best in a previous comment that when you own a high-powered tube amp, tube failure is something you just have to accept, period. If you are not prepared for this, perhaps you should consider SS.
My own experience with ARC tube amps has been similarly problematic. I owned D76A amps several decades ago, and then more recently ARC Ref 300 MkIIs. I prefer the sound of KT88s to 6550s and ARC does not support the use of KT88s in their amps. One might conclude that when installing non-ARC tubes, tube failures can be more common, but I do not accept this. I’ve had failures with both ARC tubes (Russian 6550s) and my preferred tubes (Shuguang KT88). The problem, as has been noted elsewhere, is that when a tube goes, it often takes out its power resistor. Most of us would rather repair it ourselves rather than ship these beasts back to ARC. Unfortunately, the repairs require replacing the resistor from the from side of the board unless you really want to take apart a good deal of the amp. Many of us who have had this problem have shared our experience with others via e-mails and in blogs such as this. It’s not fun, but it is a reality. Most recently, I purchased the ARC 610s and I was stunned when one of the maps blew up within 7 seconds of turning it on. I sent the amp back to ARC, only to find that my other amp blew 2 within 2 weeks while the first amp was being repaired. That was the final straw for me. Unfortunately, I am not alone as this has happened to several others. What I found particularly dumb, is that ARC should have been cognizant of these failures and at the very least, designed their latest amps so the power resistors can be easily accessed for “front of board” repair. At the very least, they should have raised the resistors high enough off the board so the board does not char when the resistor blows.
While the ARC amps are exceptionally fine sounding, I am simply not willing to live with their liabilities as tube failure probability is, as I said, a fact of life in all high-powered tube amps. My solution was simple. I bought VTL Siegfrieds. Not only does VTL support KT88s in their amps, but the amp has an absolutely stupendous and smart protection system that makes replacing a tube amp- are you ready- one of the most rewarding experiences in high end audio that I’ve ever had! When a tube fails, or is about to fail, the amp shuts down and a little light appears on the front panel that identifies which tube needs to be replaced. Replacement is accomplished in about 30 seconds, and the amp is simply re-started. Voila! No muss, no fuss. ARC claims this protection circuit degrades the sound of the amp but I have not found that to be true. I can discuss sonic comparisons of the amps but that is beyond the scope of this blog. Let’s just say I am not disappointed. Both amps are truly wonderful sonically. But for me, it’s a no brainer. If I would have kept the ARC amps and continued to experience the problems inherent with tube failure in high-powered amps, I would have no brains left at all.

I wonder if the root cause is not buying the ARC tubes, and not having a certified tech install them. ARC has been around a long time, and there are a ton of used AMPS still running, and many of them have non ARC tubes and were installed by the owners. I wonder if this is adding to this issue of reliability because of the volume of these amps still in use.

Do folks have any issues when they always buy direct from ARC so that the current balance is within their factory spec?

Most people do not want to spend the money for ARC tubes as they are expensive. I won't fix an ARC amp unless I can use ARC tubes pure and simple. I have had way too many problems with tubes from other vendors and it becomes a huge headache. And yes, it can definitely cause a reliability issue.

[I got my VS115 "repaired" from the local ARC service. They told me that the amp is fine, they couldn't find anything. I heard a blast after ca. 250 hours during the warm up period -- I checked the bias and i measured at all tubes 90mA. I also asked ARC about it but they wrote to me a short text "pls. adjust the bias to 65mA". Is there a logical explanation for that ? Ok the amp sounds great but could it happen again? Please advice - thanks for your feedback]