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Re: [Amps] Cooling 77SX

Subject: Re: [Amps] Cooling 77SX
From: MU 4CX250B <>
Date: Fri, 6 May 2016 16:18:15 -0600
List-post: <">>
Hi Gary,
The 77D and 77SX use a lovely mil spec Rotron blower. I've used the
same model blower in a homebrew 8877 amp for thirty years and would
love to find another one. Unfortunately, the blower uses an AC
induction motor, and there's no easy way to adjust the blower speed. I
use a 24 VAC transformer to reduce the AC voltage to my blower, and it
kind of works but not very well.  A series resistor won't work because
it can lead to startup problems and motor overheating, without
affecting the motor rpm.

Jim w8zr

Sent from my iPhone

> On May 6, 2016, at 2:48 PM, Gary Smith <> wrote:
> As it sits now, the fan is always on at
> the maximum amount and other than when I'm
> on RTTY, the air temp from the exhaust
> rarely gets over 110 degrees.
> The fan is noisy from the air turbulence,
> the motor/bearings are as new. I would
> like to reduce the fan to a low speed and
> kick in at a higher temperature. What
> would be ideal would be for the fan to
> progressively increase the RPM to match
> the cooling need and increase as the
> temperature increases.
> Perhaps the most reasonable solution would
> be to have the fan run at a minimum speed,
> place a thermostat with probe in line and
> have it kick in at one specific temp and
> give full RPM at that point but I would
> prefer a progressive speed:temp solution.
> I've also thought another option might be
> to remove the fan & disconnecting the
> power to the motor, connecting a 20' long
> 6" duct to the exhaust vent and at the
> distal end of the duct, have an in-line
> fan.
> I can't visualize how to make a
> progressive speed solution and I'm not
> sure of a cost effective thermostat that
> would be small enough to be internal to
> the amp.
> Any suggestions, thoughts? I really would
> like to keep the fan noise down in this
> otherwise silent shack.
> 73,
> Gary
> KA1J
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