[Amps] Shaded-pole Tube Blower

[Joe Isabella]

Seems reasonable to have some kind of interlock for this -- a couple dollars worth of parts could
easily save several hundred in new tubes.  A friend of mine switched to a pair of 3CPX800s because
the squirrel cage fan came loose from the motor shaft in his Alpha.  Tubes pretty much melted.  He
was saying that he wanted to try the "P" version of the '800s, but I'm sure he didn't intend to do
it in that way.  I guess there's one good thing about the Henry blowers.   :-)

Joe, N3JI

--- "Harold B. Mandel" <ka1xo at juno.com> 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. 
> 
> 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?
> 
> I'm glad I listen for the blower in all my amps, because if I wasn't  in
> the case of the Commander, I could very well have gone into Transmit
> after waiting for three minutes for the 3CPX800A7 triodes to reach
> Pre-Meltdown temperature. There's no overtemp or breeze fail interlocks
> in these amps.
> 
> Hmmmmm....
> 
> 73
> 
> Hal Mandel
> W4HBM 
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> 



		
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