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[Amps] Use of 60Hz blowers on 50Hz mains for cooling ceramic triodes/tet

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Subject: [Amps] Use of 60Hz blowers on 50Hz mains for cooling ceramic triodes/tetrodes
From: Ian White, G3SEK" < (Ian White, G3SEK)
Date: Tue, 13 Aug 2002 22:10:39 +0100
Michael J. Tubby B.Sc. (Hons) G8TIC wrote:

>If the motor is a synchonous type then its rotational speed is related
>to the AC supply frequency. If the motor/blower operates as specified
>on 60Hz in the US then when its moved to the UK/Europe it goes
>only 5/6ths as fast (83.3%). Now if my recollection of physics is
>correct then the volume of air moved will drop by the cube of the
>drop in speed = 0.833 x 0.833 x 0.833 = 0.578 or in otherwords
>57.8% of air (by volume) - this appears to be a significant drop in
>cooling - and somewhat worrying if I am correct.
The free-air flow rate (against no back pressure) is proportional to the 
cube of the diameter, but only directly proportional to the rpm.

Since blowers for external-anode tubes tend to be running more in a 
back-pressure-limited mode, it's probably more important is that the 
maximum pressure (no flow) is proportional to the square of the rpm.

Not quite as worrying as you suggest, but plenty worrying enough if the 
blower is already on the small side.

Why not check? Time how long it takes to blow up a swing bin bag (55 
litres) over the exhaust port.

>I've looked inside my friend's Tempo 2002A - it also has a 60Hz
>motor and (for my opinion) isn't well cooled either - doesn't get
>anywhere near Rich's requirement to nearly blow the tube out of
>the socket :-) and is certainly much less cooling than what I used
>to use on my homebrew apir of 4CX250Bs some 20-or-so years
>Revcor appear to make 230/240VAC 50Hz versions of their
>products for the UK/European market.
>When supplying amps to the export market, do US manufactures
>not fit an appopriate alternative blower?
Well, Henry don't, and Command Tech don't...

73 from Ian G3SEK         'In Practice' columnist for RadCom (RSGB)
                            Editor, 'The VHF/UHF DX Book'

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