"Mike Diack" wrote in message
...
On Thu, 24 Jun 2004 19:01:42 +0100, "N Cook"
wrote:

Straight across the output of each channel of this 1985 amp
is a diac and triac, what and how do they protect anything ?

electronic hints and repair briefs , schematics/manuals list on
http://homepages.tcp.co.uk/~diverse


You forgot to mention the resistor and capacitor.
The R and C form a low pass filter - any DC that appears on the output
(either polarity) passes through the LPF, and if above the trigger
voltage of the"diac" (SBS actually) (around +/- 8 volts IIRC) triggers
the triac and crowbars the output, at which point (hopefully) the rail
fuses expire and your wooffer voice coil is saved from becoming toast.
Clever circuit - saved my bacon on more than one occasion.
M

It makes sense now - i wasn't thinking about speaker protection.
In internal failure as passing high level DC already we can assume that at
least
one output tranny has failed or seriously biased-on so crowbarring
more to fail a fuse or 2 makes sense