"David Farber"

"François Yves Le Gal"

Judging from the schematics, the output jacks are short to ground types
in
series. And yes, the wiring leads to a secondary short if no jack is
inserted.


And this secondary short won't cause any damage with the signal going
through?


** You don't get to see too many tube guitar amps, do you David ?

Nearly all Fender tube amps all have the same precaution - ie no speaker
plugged in = shorted output.

The fact is that it is more hazardous for a tube amp to be operated into an
open circuit than a shorted one. Tubes have inherent current limiting,
unlike transistors, so do not immediately self destruct when presented with
such a load condition.

However, operation into a open circuit can result is larger than normal
voltage appearing on the tube plates and consequent possible internal arcing
of the electrodes, socket bases or even the output transformer.

You may note that "Music Man" amps take an additional precaution of having
high voltage diode stacks wired from output tube plates to ground. This
prevents the plate voltage from exceeding twice the DC supply voltage under
overdrive conditions - which it otherwise will when presented with a
typical inductive speaker load.



........ Phil