It would be important that when testing any kind of such devices, use a current limited power supply. What is this? Well, OK, simply attach a filament lamp in series with the power cord, for example getting a lamp holder with two short pieces of wire and a couple of crocodile clips in their end. Remove the fuse and connect the lamp in the fuse holder. Much like in the Mission Impossible series, when the black man make illegal connection to phone lines.
Ok, when such a device is ready, place a lamp of once to twice the power expected to be draw by the amp. When powering up the DUT, the lamp will show a short flash while charging the supply capacitors, and then it will go almost dark. This is the normal condition of the limiting action. As the filament increases quickly its resistance with temperature, further dependent on current trough the lamp, it will protect the DUT if something tends to go wrong. So you protect amp (or DUT) and yourself if an error occurs.
Once it is OK, then, attach a resistive load to the amp. of the same magnitude of the amp needs. Say, let the amp be loaded with 4Ω @ 10W, then use a 4.7Ω @ 15 or 20W, you can parallel or series resistance to get the power and resistance needed. In case of lamp, a combination of car lamps (12V) will suffice to match the buses voltages (Say, bus = 30V, then 3 lamps will do the job.).
If with no signal, the load lamps bright or the resistances becomes hot, then the series lamp will increase the bright, telling you that anything is bad.
Do this and tell us what happens. Keep us posted.
