Jim Lesurf wrote:

In article , Nick Gorham
wrote:
Fleetie wrote:

Mind you, if there's feedback and so on happening round it all,
goodness only knows.


Its not a feedback issue, just inductors at play.

Not quite. The o/p transformer is a pair of *coupled* inductors, and there
may be feedback from either/both sides. This may then control the voltage
gain and prevent problems. Depends upon the details of the design. Removing
the speaker load may drop the current levels, but this does not *guarantee*
that the plate swing will rise to a dangerous level. There is a risk of,
this, though. So you must assume it possible with an 'unknown' design.

I've certainly seen the classic output stage burnout occur where feedback *was*
taken from the secondary side - so I wouldn't advise that as an indicator of it
being safe to hot swap.


Graham