> >
> I've used the indicating strips to check the temperatures on a 3-500Z in
> a SB-1000, with quite interesting results.
>
> As most of you will know, the SB-1K has a large muffin-type fan in the
> center partition wall, blowing directly onto the 3-500Z. Cool air is
> sucked in through holes in the side to the cover, which kind of direct
> it through the electrolytic stack and around the transformer before it
> reaches the fan. Exit of hot air is through holes in the side of the
> cover, on the opposite side of the tube to the fan, so the air has to
> flow around the tube to get to the exit.
>
> The tests were not very scientific because the only strips available
> were 211-260C, and at $1 a time I wasn't going to burn up too many.
> However, I did try to keep the DC/RF conditions constant, with the anode
> at medium red heat.
>
> Without the cover - so the air was blowing onto the upstream side of the
> tube, but then going wherever it wanted - the upstream side stayed at
> 220-230C but the downstream side very quickly went off-scale.
>
> With the cover, the total airflow decreased due to the additional
> back-pressure (you could hear the fan rpm drop)... but the upstream
> temperature stayed pretty much the same as before, and the downstream
> temperature came down dramatically - it was maybe about 50C higher than
> the upstream side (it only just went off-scale, but much more slowly
> than before).
>
> Evidently without the cover the air was not coming around to cool the
> downstream side of the tube. With the cover, the exit holes close to the
> downstream side of the tube were forcing the air to come back around.
>
> That makes some kind of sense, but it has made me rather suspicious of
> blowing air onto one side of the tube without also making sure some air
> gets around the other side too.
>
> //One of the principal advantages of Flotherm (which actually comes from
> the U.K.) is that all this can be very closely modeled, if you have the
> dimensions of all components, covers, shields, etc, as well as the power
> dissipation of all major components. That allows you to scientifically
> predict the proper placement of baffles and air deflectors in an
> enclosure. Often times, fifty cents worth of sheet metal riveted into
> strategic positions saves fifty dollars on more powerful air movers, or
> five hundred dollars on new components! -WB2WIK/6
>
>
> --
> 73 from Ian G3SEK Editor, 'The VHF/UHF DX Book'
> 'In Practice' columnist for RadCom (RSGB)
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