I don't know..... Sometimes it's just luck of the draw. People tried to warn me away from buying a re-issue V4B, now that Ampeg production had moved to the Far East rather than made in the USofA. I bought one anyway. Touch wood, haven't had any issues. The only gripe I have with Ampeg, is after me explaining to them that I maintain my own gear, am qualified electronic engineer and have been building my own tube amps for 20 years..... could I please have a circuit diagram..... Don't worry I won't be the ambulance chasing moron that electrocutes himself and sues you...... The company line, "we won't supply circuit diagrams for any current product, only out-of-production"..... Not that I couldn't trace the circuit out myself in half an hour, if I needed to, but that isn't the flippin' point.