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Re: [Amps] Cooling 77SX

Subject: Re: [Amps] Cooling 77SX
From: ros <>
Date: Sat, 7 May 2016 20:59:23 -0500
List-post: <">>
Just use a triac and a pot. and you have have a variable speed fan.


On 5/6/2016 5:18 PM, MU 4CX250B wrote:
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

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.



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