2 wrote:
>
>>
>>2 wrote:
>>>Red or green ink turns toast brown at high temperature. In a typical
>>>SB-220 (blowing fan) or TL-922 (sucking fan), the marking ink on the
>>>3-500Zs is still in 'mint' condition after even a decade of use.
>>
>>Can you remind us where the markings are in those two amps, for each of
>>the tubes, in relation to the 'upstream' side? (Just wondering how much
>>difference that makes.)
>>
>â?¬ Blow air on one side of a cylinder and it flows smoothly around the
>cylinder. Thus, it does not matter where the ink is placed on the glass.
> Have you tried blowing out a candle with a cylinder betwixt your lips
>and the flame?
Yes, I'm aware that happens - but what that party trick demonstrates is
that at *low* velocities the airflow remains attached to the surface and
flows smoothly around it to join up again at the far side.
Unfortunately that isn't at all relevant to forced-air cooling, where
the airflow is very turbulent and the flow pattern is quite different.
Air is blasted at the upstream side of the tube, cooling it well, but
the flow breaks away from the surface half-way around to form a
turbulent wake. The downstream side is only cooled by eddies in the
wake, and there may even be negative pressure on the opposite side.
There is absolutely no doubt that cooling is less good on the downstream
side. The only questions are: how much less good, and does it matter?
That's why I was looking for separate evidence whether the color of the
markings is dependent on the orientation of the tube.
73 from Ian G3SEK Editor, 'The VHF/UHF DX Book'
'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.com/g3sek
--
FAQ on WWW: http://www.contesting.com/FAQ/amps
Submissions: amps@contesting.com
Administrative requests: amps-REQUEST@contesting.com
Problems: owner-amps@contesting.com
|