[Amps] Alpha vs Henry

[Ian White GM3SEK]

Roger (sub1) wrote:

>
>One other point, I've seen the question raised about how much pressure 
>was a fan generating.  For a given tube and existing system you can 
>treat air flow and pressure the same as voltage and current. IF you are 
>getting the required air flow you MUST have the required air pressure. 
>Insufficient pressure and you will have insufficient flow.  Get the 
>proper flow and you will have the proper pressure.
>
>IF the radiator is plugged or partially clogged you will have high 
>pressure and low flow. But again, it the flow if proper then so is the 
>pressure.
>

Air flow rate is what really matters in cooling, and all data sheets for 
air-cooled tubes will state the minimum volume flow rate required. 
Pressure drop is only an indirect way of measuring the volume flow 
rate... and actually a very poor way.

Pressure drop measurements in real amplifiers are very prone to errors, 
because the reading will depend critically on the orientation of the 
manometer pickup tubes relative to the air flow. We have no idea what 
the tube manufacturers did to minimize those errors... or even if they 
were aware of them. Because of all these problems, pressure drop is 
probably the wrong thing for us amateurs to measure.

It's actually MUCH easier to measure the volume flow rate directly. No 
elaborate equipment is needed - simply time how long it takes for the 
outlet air to fully inflate a large, lightweight plastic bag. With a 
little care you can measure the volume flow rate within about 10%, which 
is far more accurate than a pressure measurement.

The original idea came from George Daughters K6GT, and details are right 
here in the AMPS archives:
<http://lists.contesting.com/archives//html/Amps/1998-03/msg00172.html>



-- 

73 from Ian GM3SEK
http://www.ifwtech.co.uk/g3sek