[Amps] Shaded-pole Tube Blower

[Harold B. Mandel]

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