[R-390] DC Fan Noise

[n4buq at knology.net]

Okay, I'll bite.  What's a 3DW7A/D?

Barry - N4BUQ

> 3DW7A or 3DW7D.  Tube-size COOL-RUNNING plug-n-play.
> Schematics on request.  I'll sell you a programmed PIC for
> the latter for $10.
> 
> 73,
> Dave Wise
> 
> > -----Original Message-----
> > From: r-390-bounces at mailman.qth.net
> > [mailto:r-390-bounces at mailman.qth.net]On Behalf Of n4buq at knology.net
> > Sent: Friday, April 07, 2006 6:37 AM
> > To: Tim Shoppa; r-390 at mailman.qth.net
> > Subject: Re: [R-390] DC Fan Noise
> > 
> > 
> > The reason the IF deck is involved is this project is a 
> > replacement for the 
> > ballast tube.  It is intended as a plug-n-play substitution 
> > for the ballast 
> > with the added advantage of having a small fan.  The fan 
> > cools the dropping 
> > resistors as well as anything else in its path.  If it's 
> > going to be noisy, 
> > though (these are new fans), then I may just have to forego 
> > the fan idea.  :
> > (
> > 
> > Barry - N4BUQ
> > 
> > > > I've been working on a project that will power a small 
> > fan on the IF
> > > deck.  
> > > > I'm using the 26.2VAC supply through a single diode to a 
> > 24VDC fan. 
> > > This 
> > > > yields about 11.5VDC (at least that's what my Fluke meter 
> > shows).  I 
> > > > realize this is half-wave DC so 11.5 is an "averaging" value.
> > > > When I hooked it up last night, my Grundig Majestic 
> > nearby picked up
> > > noise 
> > > > from the fan motor.
> > > 
> > > I think this is inevitable when you drive a commutating 
> > motor (unless
> > > your 24VDC fan is decades old, it is probably solid-state 
> > commutation).
> > > 
> > > I don't think it has a lot to do with the pulsating half-sine drive.
> > > 
> > > An entirely different 24VDC fan may be much better or much worse,
> > > hard to say without trying.
> > > 
> > > If you can, try to find a small AC fan. 24VAC units do 
> > exist but are not
> > > real common. It's vaguely possible that 24VAC may work to slowly
> > > turn a 120VAC fan, but even if it'll keep it turning it 
> > probably won't
> > > start.
> > > 
> > > Big AC fans (I'm thinking of 10" or 14" rotrons etc.) work 
> > OK without
> > > making a lot
> > > of wind noise if you use 120VAC to drive them and a 
> > dropping resistor.
> > > 
> > > A little odd that you're aiming it at the IF deck. Yeah, 
> > there's a lot
> > > of
> > > tubes in a small space there. I honestly do not know if 
> > crumbling foam
> > > in the mech filters is accelerated or not by "typical" heat 
> > on the IF
> > > deck.
> > > 
> > > Tim.
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> > > 
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