Never had speakers ( 4-16 ohm imp.) act like this. Often when test running
a set we would hang a pair of cheap TV speakers on it & never had
a problem except if the PA shorted & popped them. No great loss....
This was on anything from tube amps through STK amps & big discrete
component PA's.
Since the amp wants to see a given SPKR impedance to be most
efficient any SPKR problem should show only reduced volume IMHO.
Other thing is you seem to infer the STK has been changed ??
If so its almost impossible to find REAL ones. Almost all are Chi-com
bootlegs that barely work.
From two sources i trust.
https://www.youtube.com/watch?v=EZJjqpDaSZs
https://www.youtube.com/watch?v=zvx07QdAoig
73 Zeno
LFOD !