Problems with Orange AD140TC amp

[suburbanmisfit]

I purchased this amp used and it worked fine for 4 months then all of a sudden it crapped out. By crapped out I mean, amp powers on>tubes glow>but the amp only produces sound when turned all the way up and it is not a loud sound at all; it also breaks up very quickly and sounds fuzzy(on both channels)

I have tried the following, replacing all the power and pre amp tubes, tried multiple cables(that all work fine on other amps) and multiple guitars. I have also tried two 4x12 cabinets.

I am guessing there must be a problem with pre amp tube sockets? I am pretty sure it must be one of the problems listed here:

http://www.geofex.com/ampdbug/lowpower.htm

I am prepared to take it to a tech but I'd feel a lot better if I could atleast get some ideas or insight as to what might be the problem. Also if you have any idea of the type of parts/costs involved to repair this that would be helpful. I know the authorized orange amp tech that I have to go to charges $40/hour + parts. I dont want to end up basically buying a new amp with the costs of repair.

Thanks.