[Drake] Cooling fans - blow in or out?

[fkamp at comcast.net]

"Chris Codella, W2PA" wrote:
> 
> I'm about to install a cooling fan on my T-4XB and TR-4, having seen
> many ways to do it.  But what's the concensus on the list about blow-in
> vs. blow-out?  I've seen it recommended both ways.
> 
> The only recommendation I saw that also included a rationale was one
> posting where someone said to orient the fan blowing out because the
> only time one wants to blow in is if there is a forced-air handling
> design built in, as exists in many amplifiers (i.e. chimneys, etc.).  I
> must say that most rigs I see with factory mounted fans on the back that
> also don't have air handling features inside, do in fact blow out, not in.
> 
> What's the concensus among the Drake crowd here?  Please don't recommend
> one way or the other without giving a reason.
> 

I have a T4X and a T4XC. Both transmitters have fans installed to the
back of the RF cage with bolts through existing holes in the cage.  Both
fans blow in because that places the finger guards on the outside where
they belong.  While it was certainly possible to remount the finger
guards and install the fans to reverse the airflow, I did not consider
the additional effort necessary.

I used three inch fans designed to be run on 12 vdc.  I run them at
about 7vdc.  Less noise and just enough airflow to have a significant
cooling effect.  The area above the finals is noticably cooler than the
rest of the cabinet when the finals are idling.

The fans are mounted very close to the finals.  The cabinet has an
abundance of holes so it does not have a significant effect on airflow.
Because of this, I dont think there would be any more or less cooling
regardless of which way the wind blows.

I have heard folks suggest that a fan blowing into the cabinet will suck
in dust and dirt but the same thing would happen with the fan blowing
the other way.  The dust and dirt would just come from a different
source through the holes in the cabinet.  Besides, it would much easier
to install a dust filter on a fan that blows in than try to filter air
being sucked in through the numberous holes in the cabinet.

Forced air cooling designs dont use normal fans.  They use squirrel cage
blowers and deliver far more air than is needed for cooling a Drake
transmitter.  

I have used fans on the equipment here for over five years with good
results.  Never had to change a final even though I sometimes run RTTY,
but that may also be due to the fact that I replaced the 6JB6s with
6146s. 

Regards,
Frank Kamp
K5DKZ