Detta svar fick jag på Hoffman forum. Nån som kan bedöma om han vet vad han talar om? Enligt hans mening så kan inte en öppning mellan primär och sekundär bränna högtalarna. (Nya element är Jensen JCH 10/35)
> short circuit from primary to secondary
That should not be fatal to speakers.
Short from B+ to one side of speaker winding.
One end of speaker winding is grounded, and speaker winding has very low DC resistance (<1 ohm). So about 7/8 of any DC current from B+ goes through winding, not speaker.
What is the most current that B+ can supply? 130 Watt output, say 240 Watts of DC from B+ normally, so 0.34 Amps steady-state. A transformer can maybe supply 10X rated current into a short. 3 amps.
7/8 of that 3A in OT speaker winding, 1/8 in speaker. 3/8 or 0.375 Amps in speaker. 0.375A^2*8r is 1.13 Watts of power in the speaker. A "130 Watt" speaker array can stand 1.2W forever.
Assume a *second* defect. OT speaker winding has gone open. All the 3 Amps possible from B+ flow in speaker. 3A^2*8 is 72 Watts of heat in the speaker. A "130 Watt" stage-speaker array "should" survive 72W for many seconds, though if DC the huge excursion will stretch the surround and just-maybe jump the voice coil out of the gap. It is also a race between speaker damage and melt-down of the Power Transformer supplying 10X its rated output.
So it could happen; but I'm real doubtful on the chance of two different faults (short P-S and open S) and in an amp which often works fine.
> amp suddenly got silent for three seconds or something and then sounded again, but with distortion at low frequences. And the speakers were hot!
Something is going on, but I don't have a glimmer.
The 3-second silence, then part-life, ought to be a clue, but I'm blank.
I assume the speakers are good hi-power jobs. (I've seen 100W amps with $30 30W speakers installed thoughtlessly then blown.)