Heat can be a friend but it's usually our enemy in so many ways. Yet, to
prevent melt-downs and dangerous conditions it is the easiest indicator of
failure to detect and manage.
A carefully placed ptc resistor embedded into a transformer primary or in
other hot zones works wonders and makes compliance with safety laws very
much easier. They are cheap and reliable and very popular over here. For
the sake of a $1 that Alpha and any other amplifier would have powered-down
safely, well before any damage could have occurred. Cycle the power and you
are back in business immediately. Magic devices.
In our safety standards it has been a mandatory test to put 15% excess mains
supply voltage on an article, prevent or restrict cooling, put all controls
into the worst condition and then measure mains transformer primary
temperature rise (usually the resistance method) after a suitable
stabilising period. That temperature must not exceed figures laid down for
the type of wire used in the primary.
It's likely that a pa will exceed proper temperature limits before the mains
transformer gets to its limit, and it could be controlled with a simple
thermostat, thermal fuse or ptc resistor in a low level circuit.
Is this done in amateur linear amplifiers?
A responsible manufacturer of any equipment places safety first and
compliance law is written that way. It should make equipment practically
fool proof.
David
G3UNA
>
> Any fool can overbuild a product. Good engineers know when to stop,
> and good engineers get paid good money to get it right.
>
> 73, Bill W6WRT
A buddy accidently had his cat fall asleep on his footswitch for 2 hrs.His
87-A was pumping out a 1.5 kw FM cxr on 29.650 mhz. He had the optional
cooling fan.The RF deck had turned into molten glop ! Jim VE7RF
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