Needing service for Acoustic Research solid state preamplifier

His pre is Acoustic Research not Audio Research. 

AR only made 2 preamps: C-06 // from 1986-1989 and Limited Model 2 - 1993.

What does that have to do with service dill? Anyway, it's probably not an exotic design, and if you say what state you live in, I'm sure that you will get a recommendation for a good service tech near you.

https://cmtechsupport.com/

CM Tech also offers expert repair service on all AR/Advent loudspeakers and amplifiers. Please contact us for more information.

My point of mentioning, the only 2 models, is they where not made in  great quantities, especially the model 2. I thought it was odd that someone might want to sink money into these preamps. 

I also think the OP might mean Audio Research which would make more sense to service & upgrade. Maybe by my mentioning this the OP would chime in here and clear things up.