Protective circuits: There are several protections against excessive cur-
rent. Transistors Q4 and Q7 are current limiters. If a short occurs across
the audio output,
the following sequence of events will occur: (1) the DC vol-
tage across Resistors R29 and R32 will drop; (2) this drop will drive Transis-
tors Q4 and Q7 into conduction; (3) the output of Q4 and Q7 will limit the
drive to Transistors Q5 and Q6; and (4) the. reduced output from Q5 and Q6 to
the power transistors will reduce the overall gain (and, thereby, the total
power) of the amplifier. An excessive current surge will cause the fuse to
open. In the 28-VDC supply, a short circuit on the DC output or a DC load that
draws significantly more current than 1.2 Amperes will cause Thermal Breaker
CB2 to open within 70 seconds. It will try to reset within 15 seconds, then
continue opening and closing until the short or the excessive load is removed,
at which time it will remain closed for normal operation. A more serious prob-
lem will cause CBl to open;
it must be reset manually.
