[ETO_Alpha] Alpha 87A/89 Muffin Fan Capacity

[Paul Christensen]

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
______________________________________________________________
ETO_Alpha mailing list
Home: http://mailman.qth.net/mailman/listinfo/eto_alpha
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:ETO_Alpha at mailman.qth.net

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html