[ETO_Alpha] Alpha 87A/89 Muffin Fan Capacity

[Jim Garland]

I too have been looking for a low volume very quiet muffin fan for
exhausting air from a desk compartment that houses a computer. I recall a
number of years ago that there was a muffin-type fan called a "whisper" fan
that was extremely quiet and ran on 120VAC. However, I've not been able to
find it. I ended up just choosing the quietest fan in my junk box and
slowing it down with a light dimmer, but it's still too noisy.

Re 12V DC fans, I recommend using a zener diode instead of a resistor to
slow them down. One doesn't lose starting torque that way, which aids
startup at reduced voltages.  120VAC fans can be slowed with series
capacitors, though I've normally used filament transformers to buck 120VAC.
Again, this preserves starting torque.

73,

Jim W8ZR

> -----Original Message-----
> From: eto_alpha-bounces at mailman.qth.net [mailto:eto_alpha-
> bounces at mailman.qth.net] On Behalf Of Paul Christensen
> Sent: Thursday, March 26, 2009 4:45 AM
> To: ETO_Alpha at mailman.qth.net
> Subject: Re: [ETO_Alpha] Alpha 87A/89 Muffin Fan Capacity
> 
> About two years ago, I rebuilt my Alpha 86.  (BTW, Glenn and Molly were
> very
> helpful during this time.)  Part of the re-build consisted of finding a
> fan
> that was reasonably silent, but produced adequate air flow.  I must have
> experimented with nearly a dozen fans.
> 
> All ball-bearing fans were too loud.  I ended up with a sleeve bearing
> type
> at about 50 CFM.  Even then, the noise could be heard over the blower.  I
> ended up slowing the rotation by placing a 10W chassis-mounted power
> resistor (Dale/Vishay), in series with the positive fan lead.
> 
> My next attempt will be inclusion of a temperature-sensing switch.  I had
> a
> similar issue in cooling an HP 6652A linear station power supply.   I
> decided to try the circuit that appeared in the June, 1994 issue of QST.
> This circuit works very well and uses MOSFET switching of the fan.  A
> 10K-ohm NTC thermistor is used to bias the junction of a generic NPN
> switching transistor that activates the MOSFET.  Settings are repeatable
> and
> the circuit is very stable in an RF environment.
> 
> Paul, W9AC
> 
> ----- Original Message -----
> From: "Glenn AE0Q" <gm5bkc at gmail.com>
> To: <ETO_Alpha at mailman.qth.net>
> Sent: Wednesday, March 25, 2009 10:32 PM
> Subject: Re: [ETO_Alpha] Alpha 87A/89 Muffin Fan Capacity
> 
> 
> Hello Bob,
> 
>  When we (Alpha) recently posted a fan kit on eBay I got the specs
> for the fans that we currently have, here is it all:
> 
> "External Muffin Fan Kit, 230V 50/60Hz, 82 CFM;
>  for mounting on the rear opening of the Alpha 87A and 89 Amateur
> Radio amplifiers, pre-wired with lug connectors and includes mounting
> hardware.  This fan pushes cooling air into the amplifier, aiding air
> flow through the internal tubedeck blower and reducing the exhaust air
> temperature of the tubes."
> 
>  The CFM rating might be slightly different from the Etri 5-blade
> fans that we used until last year.
> 
> 73 - Glenn AE0Q
> 
> On Wed, Mar 25, 2009 at 8:02 PM, Robert Dorchuck W6VY <w6vy at yahoo.com>
> wrote:
> > Anyone know the specs for the optional muffin fan for the Alpha 87A or
> 89?
> > In particular the CFM rating.
> >
> > Thanks,
> > Bob W6VY
> > ______________________________________________________________
> > ETO_Alpha mailing list
> 
> --
> "Remember, any tool can be the right tool!"   Red Green
> 
>  AE0Q / V31RY              ex: GM5BKC, ZB2WZ, SV0WY, WA0VPK
>  ae0q at arrl.net      --SOWP 5558-M, ARRL LM, QCWA LM, OOTC, NCVA--
> http://www.radiotipsandtales.com
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