I’ve just had a look at the website for Northumberland Archives and see that they offer a Personal Mentoring Service, it is a bit pricey at £52 for two hours, but it could be just the thing to get you over a brick wall. There are the usual pages of opening hours, user guides etc. and the catalogue includes part of the collection and is being added to regularly. Of interest is that some of the documents have been scanned and are available online.

http://www.experiencewoodhorn.com/collections/