[Amps] Coupling a blower to an air system socket

[Jim Thomson]

Date: Sun, 17 Mar 2013 15:37:50 -0400
From: "Roger (K8RI)" <k8ri at rogerhalstead.com>
Cc: amps at contesting.com
Subject: Re: [Amps] Coupling a blower to an air system socket

>> One thing to remember about external anode tubes. They often have
> cooling requirements listed as so many cfm at a given back pressure,
>>
>> I do not know of any way to achieve the required air flow at a reduced
> back  pressure other than an exhaust fan reducing the exhaust pressure thus
> making it a little easier to get more cooling air through.
>> I believe Emtron and OM both use this approach on some models.

###  Roger, you have missed the basic concept of the k2riw design.  It’s
in every arrl handbook, check it out !!   IF you cool the tube in the conventional
EIMAC method, you need one helluva lot more pressure when trying to cool
tubes like 4CX-250B’s..... vs cooling via the k2riw scheme.   The bottle neck
with the eimac method is the huge restriction at the socket.   Then you have the
restriction of the anode fins themselves.   The drop across the anode fins is useful
since that’s what cools the tubes.   the drop across the socket is immense, way
more than actually required to cool the base. 

##  with the eimac scheme, the two restrictions are in SERIES.   With the k2riw
scheme, the same two restrictions are now in PARALLEL. 

## end result is the pressure requirements of the blower are greatly reduced !! 
Check out the specs to cool 4 x 4CX-250B’s.   They don’t need much cfm,
but they need one helluva lot of pressure.   High pressure, low cfm blowers
are not easy to come by.   High pressure blowers usually make one heck of
a lot of noise.   You need high rpm blowers to get high pressure. = noise.  





This is not arguing whether some other method is adequate, or even what 
is adequate, but that to get that air flow "Through" the anode requires 
that specific delta T across the anode cooler.

##  correct, but do it the eimac way  vs the k2riw way... and  cfm
is the same in each case, BUT the back pressures are way different.


What the manufacturer says is needed and careful calculation may result 
in answers that are quite different. Still this does not change the 
fact that to get X airflow through a given anode structure requires Y 
pressure just as to get X current through a given resistor takes Y 
voltage (or pressure/potential difference)

## ok, try this.   two resistor’s  in PARALLEL   vs same two resistors
in SERIES. 

##  2 x  50 ohm resistors in SERIES = 100 ohms.   The desired  current
through em is 1 A.     We need 100 V to do the job. 

##  Put the 2 x 50 ohm resistors in PARALLEL = 25 ohms....and now we only need
50 V to get the same 1 A  flowing through EACH resistor.

##  great, now we only need half as much voltage ( pressure)  to do the job. 

## Eimac has come up with dumb designs before.... like their metal sockets for
4-1000’s etc.  remove the pins, and transverse slice the entire base off, then
reinstall pins.  required pressure just dropped a huge amount. 

## Eimac makes tubes, and the end user’s  job is to make em work, end of story. A lot 
of the eimac chimney’s are designed poorly, resulting in increased blower pressure requirements.

Jim  VE7RF





73

Roger (K8RI)