[R-390] WAS Alternative to IERC tube shields - NOW fans

[rbethman]

I responded directly:  If Someone writes directly, I provide them their 
privacy as a courtesy!

To keep from worry regarding resonance with a cap, I place the resistor 
with its body against the body of the fan.  That is actually its duct, 
as these are based upon close clearance to maximize flow.  So it 
essentially cools the resistor also.

It becomes a trade-off.  I had one of these already installed on a tube 
radio in my pre-Amateur days.  I was licensed as a General in the fall 
of 1980.  I had been, [Horrors!], a Chicken Bander prior to that.

Bob - N0DGN


List Member wrote:
> Hi Bob,
>
> You recently wrote:
>
> >The typical brushless type muffin fans that most of us use are indeed
> >the 4" X 4" (approx), 120VAC fans that "normally" scream.  One puts a
> >large sand encapsulated resistor in the hot leg feeding it.
>
> May I suggest instead the use of a 400-600V capacitor?
> The cap's reactance will drop the voltage without the heat
> a resistor produces. Select cap value as needed to get the
> desired fan speed. I seem to remember using values of .5-2mfd
> or so, but it has been _many_ years and memory fades.
> One caveat: make d**n sure the cap doesn't series resonate
> at 60cps with the motor inductance. You will literally be blowing
> smoke for a while.