[time-nuts] 5070B once more.... (actually 5370A fans)

Richard (Rick) Karlquist richard at karlquist.com
Thu May 21 16:25:51 UTC 2009


Mark Sims wrote:
> I have done quite a bit of work replacing fans in old equipment with modern fans.

   I have never seen a case where replacing a hurricane level fan with a 
whisper

  quiet fan made any real difference in the cooling inside the unit... 
typically

one sees less than +/- 5C difference anywhere inside the box.  Some places

  get a bit cooler and some a bit warmer.

This is incorrect.  ECL components require a minimum airflow velocity
that is rather high.  The purpose of the large fan is to maintain this
velocity.  If a smaller fan is used, the ECL components will get hotter,
even though the air flowing past them is not much hotter.  When you say
the fan didn't make any real difference in cooling inside the unit, did
you measure the temperature of the ECL DIP's?  "Modern" fans obey the
same laws of physics as the original equipment.  They don't magically
produce more airflow for less noise.  It would also be a mistake to
assume automatically that all HP equipment is overdesigned.  I remember
one logic analyzer was referred to internally as the "logic furnace",
which had a high failure rate.

Rick Karlquist N6RK



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