I am experimenting with a new 2 x GI-7B amplifier using muffin fan types
to establish whether I can get reasonable air flow...Test 1 was using a
pair of 240 volt 3.5 inch fans mounted beneath the tubes blowing over
the cathodes exiting through chimneys and out the top of the
amplifier...Result is pretty dismal..Muffin fans don't like restricted
air flow...
Experiment 2 was mounting a pair of the fans above the tubes sucking the
air through the coolers...At first I thought the flow wasn't much better
but discovered that the exiting air is thrown radially rather than
straight upwards...Of course as there is no concentration of the output
upwards one can only guess how effective the flow is...
Tomorrow, I am going to add a pair of 12 volt 3 inch muffin fans under
the base plate cathode compartment and try a push pull effect with the
240 volt fans on top..If this improves the flow I will then replace the
two top 240 volt fans with a more powerful single 5 inch muffin
fan...The fans certainly run quieter than any blower I have
tried....Suitable blowers are virtually unobtainable in VK and have to
be sourced overseas which with shipping make them very expensive..
I figure that in service running 700 watts ssb output, dissipation would
not be greater than 400 watts of heat from 2 tubes all up but this is
just a generalisation on my part...I don't have a means to actually
measure anode heat..
Running data modes for meteor scatter etc would probably strain the
friendship past 300 watts output in 30 second bursts but worth looking at..
I would be interested in other opinions..
Bob..VK3ZL..
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