>...
>With the 3-500zg, the real cooling issue is the keeping the glass-metal
>seals cool enough.Typically, the use of a muffin (or tubeaxial) fan blowing
>across the tubes isn't sufficient to allow continuous operation at the
>maximum ratings; this is why amp manufacturers (including Ten Tec, Qro etc)
>restrict the power to 650 or 800 watts respectively in 'key down' modes like
>RTTY, and also limit the maximum transmit time to about 10 minutes. Through
>the use of a better cooling system, (like an air system socket and
chimneys)...
** I have observed that the glass-tube cooling system which produces the
lowest glass temperature is not the air-sytem socket and chimney, it is
the simple split-chassis tranverse fan system that Heath used in the
SB-220. However, for Heath's method to work properly, the fan diameter
needs to be slightly greater than the overall tube height. For example,
a 3-500Z is about 140mm tall, and the Heath fan diameter is 150mm (6").
Also, the Heath cooling system is c. 20db quiter than the high-pressure
centrifugal blower needed with an air-system socket. However, the
air-system socket/chimney has one big advantage: It impresses those who
don't know what's what.
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