Can you bridge any 2 channel amp?

Kijanki, does this line of reasoning hold true for a dual-mono design with separate power supplies, transformers and heat sinks? Would impedance issues still be a factor?

Thank you guys. My reason for asking is that I've just had 3 Acoustat TNT200 stereo amps rebuilt with mono capability via internal switch. The work was done by Roy Esposito who is one of the design engineers of the amp. He assures me they are still stable at 4ohms in mono. It's not that I don't trust Roy, but you can't have too much consensus.