[Amps] Cooling 77SX

[Gary Smith]

Hi Jim,

It really is a nice blower. When I got the amp, it had a dirty set of 
blades and I was appalled at the volume of noise when it was turning. 
I used Q tips and denatured alcohol to clean the individual blades on 
both sides and then when all the accumulated crap was removed, I put 
it in the dishwasher. When I replaced it and ran it, it was far 
quieter, apparently the turbulence of the accumulated dust & whatever 
on the blades was causing turbulence and that was heard as noise.

I have a Sunbeam oven thermometer (like for cooking in the oven),  
with its probe resting in the exhaust, set up to alert when the temp 
gets to 130 degrees. This way I don't get concerned with RTTY 
contests and when I hear the beeping, I know its starting to get 
warm. I baby the amp, never abuse it and want it to last for as long 
as I do.

But as to the motor, I haven't tried adjusting it, but I thought the 
wirewound resistor with the adjustment slider, mounted to the upper 
back of the cabinet was designed to adjust the speed of the blower. 
Is that not there to change the speed of the fan?

I had been thinking of attaching another slider and switching between 
them depending on the temperature. Maybe even going as far as to have 
three different sliders on it and switch between them depending on 
the temperature of the exhaust air to change the speed of the fan.

73,

Gary
KA1J

> 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.
> 
> 73,
> Jim w8zr
> 
> Sent from my iPhone
> 
> > On May 6, 2016, at 2:48 PM, Gary Smith <Gary at ka1j.com> 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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