[AMPS] Blowers for finned tubes

[Rich Measures]

>> Rich Measures wrote:
>>
>> >However, measuring cfm requires elaborate test equipment.
>>
>
>Ian White, G3SEK wrote:
>
>> Actually it's very easy using the method described by K6GT. Simply
>> time
>> how long it takes for the outlet air to inflate a large, light plastic
>>
>> bag. (To measure the inflated volume of the bag, suspend it in a part-
>>
>> filled barrel of water, and pour in measured amounts of water into the
>>
>> bag until it's just full. The water in the barrel outside of the bag
>> supports the weight.)
>
>One way I have measured cfm  is to heat a big (few 100 W) resistor in
>the input side of the amp,
>then measure the air temperature just before the resistor, and at the
>bottom
>of the anode cooler, with a pair of thermocouples. Flow rate can be
>found
>from:
>
>Flow (cfm) = 1.76*power dissipated(W) /increase in temp (deg C)
>
>You can overun the resistor quite a bit, as the cooling air will stop
>damage.
>I ran a 300 W resistor at about 600W or so - cant recall the exact
>numbers.
>I recon you need to dissipate at least 10% of the anode dissipation to
>get a
>sensible temperature rise that can be measured accurately.
>
>Just be careful the resistor is well secured, and can not fly loose.
>
>You should idealy thermally insulate (paper would do) the
>grid/cathode compartment, so the heat only escapes up through
>the anode cooler, and not out of the amp box.
>
>Instumentation is a bit  more expensive than the method Ian mentions,
>but
>I think its easier for big tubes, where the time to fill a bag would be
>so short
>as to make accurate timing difficult. I used themocouples, since I have
>an old
>10 input K-type thermocouple thermometer, but a couple of inexpensive
>thermistors,
>measured on the resistance range of a DVM, should do the job just as
>well.
>
>As Ian has said to me in the past, air flow meausrements dont really
>need the
>highest of accuracy, so perhaps the bag method is better all round.
>Anyway,
>there are t least two methods of measuring flow that can be done easily
>at home.
>
>Any other methods  ??????
>
€  Whew.  .  .  Eimac did the work.  All one needs is a homebrewed manometer,  the Eimac spec. sheet, and a ballpark estimation of altitude.  .  

cheers
Rich...

R. L. Measures, 805-386-3734, AG6K   


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