pryso, I would think that an output transformer to some degree does protect the speaker, especially from DC offset and maybe a little from an audio signal burst if it exceeds in wattage the amount that the OPT itself can tolerate. Of course, in that case you have a damaged OPT. But with my OTL amplifiers, there is nothing except in the case of a conventional ESL, the audio transformer in the ESL affords some protection. With the Beveridge speakers, there is literally nothing to protect them if one of their amplifiers' output stage goes south.