[Amps] Shaded-pole Tube Blower

[Harold B. Mandel]

Dear Joe,


I wholeheartedly agree!

The blower, going through the 75 ohm resistor, is barely audible,
especially when the station is running and the speaker overhead
is churning out QRM/QRN.

Another hurdle is that the lower RF deck and air plenum is 
extremely difficult to access on the Commander Amp series. Last weekend,
when I had the amp apart for service, it took hours to get to the point
where I
could do surgery on the control board, and removing the entire RF deck
to get at the air inlet hole in the plenum would have involved
desoldering
the output toroid, the RF relays and removing the entire center wall
section.

Hal

On Sat, 20 Nov 2004 15:59:19 -0800 (PST) Joe Isabella <n3ji at yahoo.com>
writes:
> 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 
> > _______________________________________________
> > Amps mailing list
> > Amps at contesting.com
> > http://lists.contesting.com/mailman/listinfo/amps
> > 
> 
> 
> 
>                 
> __________________________________ 
> Do you Yahoo!? 
> Meet the all-new My Yahoo! - Try it today! 
> http://my.yahoo.com 
>  
> 
> _______________________________________________
> Amps mailing list
> Amps at contesting.com
> http://lists.contesting.com/mailman/listinfo/amps
> 
>