My Amp is Broken - Not Sure What to Do - Any Recommendations?

Distortions:  I recommend that that you formally enter a repair/service request on the ARC website.  Notwithstanding the fact that your warranty has expired, reputable equipment manufacturers will want to exhaust options available to satisfy the customer.  Since the ARC technician has already indicated there is a failure history (if not a latent defect), putting your request in text places the onus on the company to provide a formal response.  Based on my personal experience with amplifiers being blown out by lightning (electrical) and thunder (concussion) storms, I can tell you that company corporate and subordinate units really do listen and find ways to make the original purchaser happy and preserve the image of their brand.  I know it can be frustrating and time-consuming but, if necessary, you can keep going up the corporate ladder until somebody pays attention and commits to resolving the problem.  Do not simply accept the word of a first-level service technician or customer service representative, but ask to speak to their supervisor.  Best wishes for a successful outcome. 

Take ARC to task on the repair if no satisfaction  give Tom a call @ Northridge Electronics in Simi Valley Ca.   This is an old school tech who really knows his stuff and is a repairman pure and simple with no funny stuff about boutique cures or similar ilk.   

I have a Thermaltrak equipped HD220 myself and Audio Research would ABSOLUTELY refuse to return my repeated calls AND repeated emails.  The good old days of Leonard and Kalvin are gone.

A $25/hr tech... GOOD LUCK finding one who knows what the 5 pins of the thermaltrak devices are about.   

I agree, this is lousy customer service. If I did buy a new amp it wouldn’t be an ARC. Their power amps are prone to failure. They do sound good when working though

Parts go obsolete, I've had to run down a lot of obsolete parts, some companies have made products using discontinued parts, knowing before their production run that the parts had been discontinued!

If you really liked that amp, I'd contact Roy Mottram at tubes4hifi.com, he has designed many tube amps, preamps, and phono preamps. You could also contact Don Sachs, but it's unlikely that he'll do repairs, last I knew he was way behind in making his own amps and preamps. Anyway, those guys are big on tube circuit design and may have already worked on your problem for someone else.