[Amps] Shaded-pole Tube Blower

[R.Measures]

On Nov 20, 2004, at 3:10 PM, Harold B. Mandel wrote:

> Pat Stein at Commander Amplifiers readily admitted that the Dayton 
> 4C761
> shaded pole turntable-type blower motors run very hot in the Commander
> amplifiers, like 180 to 200 degrees F.

Dayton motors are a big advantage on Antarctic DX-peditions.
>
> One of the fresh air inlet grates is directly below the fan motor so 
> there is some
> cool air going across the motor body.
>
> I didn't find any lint or debris in the bronze bushings and there was 
> some oil
> still floating around and the armature spun freely. I can't imagine 
> why the fan
> refused to start other than in the new series of Commander amps the 
> fan motor
> is on the soft-start circuit AND has a 75 ohm resistor in series with 
> one
> of the fan motor leads (that is shorted out for a fan speed increase in
> transmit).
>
> Since the technical information about shaded pole motors does say they 
> are
> hard to start, I wonder if the combination of series resistance and
> soft-start circuitry sometimes prevented the motor from starting?

Hal -- My SB-220 fan's shaded-pole motor has a 75-ohm resistor in 
series with it when the exhaust air-temp is cool.  When the air gets 
hot, the 75-ohm R is shorted by a thermostat to speed up the fan.  
There has never been a problem with the motor not starting,
>
>  ... ...
Richard L. Measures, AG6K, 805.386.3734.  www.somis.org