> "Here’s the idea...The cut-out mechanism would be one of these TO220 sized
> bimetal switches. They are available in a variety of trip points."
That's a concept I used back in the '70s to engage a boxer fan on the back
of an HW-101. A precision cylinder thermal switch was used to measure
temperature inside the 101's PA compartment. In that case, a switch with a
two-point hysteresis level was needed to keep the fan from toggling on/off
more than necessary when the temperature was at the sensor's threshold. In
your application, that wouldn't be a concern.
A companion idea involves monitoring the stack temperature inside the tube
chimney. The ACOM 2000A uses a LM35 (or its equivalent) on the Silicone
chimneys. The LM35 is a precision Celsius sensor, whereas the LM34 provides
output in Fahrenheit. There are no external components, although usual
bypass C practice is a good idea.
http://www.national.com/ds/LM/LM35.pdf
Both devices are available in a small 3-lead TO-92 package and are immune to
RF. They can be found in commercial temperature sensors used at high power
broadcasting facilities. There's no calibration either. The output
voltage is a linear function of the actual numeric temperature change.
Since the TO-92 is so small, a 1/8" hole can be perforated into the side of
the Silicone chimney (on ceramic VT amps), then use Silicone RTV to keep the
sensor in place, while keeping the sensor leads dressed adaquately away from
HV.
So, with minimal effort, one can have a low-cost temperature failsafe with
monitoring capabilities.
Paul, W9AC
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