Repair resource for Audio Reseaerch Ref 150 amp

Can anyone suggest a service repair resource for my amplifier?

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First stop is Audio Research. They offer great service for even their oldest models, and sometimes phantom upgrades beyond the model's ending configuration.

If for some reason you do not want to go the factory route, then Bob Hovland in Los Angeles is a great option. I can refer you if you don't have his direct contact.

Do you still have Bob Hovland's contact information if he is doing repair work?
Send it back to Audio Research (ARC).

 Send it home to ARC. 213cobra is right, ARC makes minor changes as they go. They will sometimes incorporate these updates in your piece while it is being repaired. They did with my Ref 5se that was under warranty. They will also make sure that it is working properly and sounds as good (or better) than the day it left the factory. It is worth any extra time and expense to have it done right.