That's a puzzle. Solid state amps are normally immune to open circuit output. They may fry though if the output is shorted.MikeMl, I have had to fix a lot of car stereos that were turned on without speakers, or only one speaker with blown oututs. lately, the designs have improved so that they dont do that as often.
hey, thanks for the replys, its all getting much clear now....LvW veenife,
sorry, but again I must note that your question is not yet clear.
1.) Are you interested in input or output impedances or both?
2.) Is your request related to the active unit (tube, transistor) alone or within an amplifier circuit? This makes a big difference!