I have a chance to pickup a PF500 for $75. Although the unit powers on, there isn't any sound. Is it worth purchasing the unit and having a technician repair it? Or should I just look past it an invest in something else? I will have to ask the seller if this is a early model, as I remember Ampeg having some problems with these in the past. Did they ever resolve the issue with the older models? I have tons of amps, and this isn't a need. I was just browsing along and found someone who wanted to get rid of it. Could this end up being a good investment down the road?