I recently bought a used Lonestar in mint condition that was on consignment at Atlanta Discount Music. It played fine in the store, but after a few days residing in my studio it started losing output intermittently...and now I can't get any output from it other than some low volume from the preamp section. I tried replacing the output tubes with some brand new EL34 groove tubes (and yes I switched the bias to EL34), but this didn't help any. Could it be a bad rectifier tube (5U4/GB) causing this? I put in an order for all new Mesa tubes (6L6's and 5U4) to try to get it to work. Or do I need to just go ahead and ship it back to Mesa Boogie for a warranty repair?