Hi Damien:
I perhaps got a little too annoyed at reading some of the cr*p that gets
passed off on line as worthwhile technical information. Anyway...too
issues going on really.
1. Do the AC4 or any other Drake or similar units need fans?
2. How to implement fans..especially blowing in or out.
For 1. Do they need fans. I would say, technically no..most have
lasted over 40 years without them....
The fact is however, that the service life of electronics is extended
greatly if they are kept cooler. In the 60s, adding a fan to a rig was
an expensive proposition..thats why many manufacturers made them
optional. I am sure Drake never had an engineering discussion about
"lets make sure these rigs are still working fine in 2010 !! They did
however have discussions about maximizing performance at chosen price
points. Today, adding a quiet, small fan is trivial...so I opt to do
it..as do many others. The only real issue with the AC4 is that holes
must be drilled in the cover. I got over that once I replaced all of
the "original" filter caps, rectifiers and bleeders with the Heathkit
shop upgrade board. I use my Drake rigs; a lot. When they are on, they
stay on for 12-16 hours at a time and frequently I run RTTY contests, or
CW contests with them. If a collection just sits there and never runs
more than a couple hours a month, I'm sure there is not much need for a
fan--anywhere in the system. Even the PS7 however, has an optional
location for an 80mm exhaust fan. And it is a large open enclosure
compared to the AC4 and also has perforated covers.
It is interesting to note that the AC3 had no cover. I suspect that
Drake felt some safety pressure to cover the PS. Also...the fact that
the cover on the AC4 is aluminum I suspect is not just coincidence but a
thermal decision as well. This could have been perferrated steel like
the rest of the line. Why not? I suspect that the solid aluminum cover
is better thermally..aluminum is MUCH more conductive than steel. Its a
big heat radiator.
As for question 2, all of these small fans are designed to move air in
only one direction. They also are designed to work with a very small
negative pressure on the draw side...there ability to function drops to
nearly zero if they work against a positive pressure on the exhaust
side. SO...unless there is zero restriction in the path, they should
always be run pulling air and not pushing it. A simple experiment can
prove this. Put a 40W lightbulb in a cardboard box and put a fan on it
pointing in. seal it up with a thermometer and turn on the fan and lite
and watch the temp. Poke a few small holes in the box and watch wat
happens....not much. Now turn the fan around so it pulls air out..air
will be drawn into the holes you made..the temp will drop fast.
Or just remember what happens when the bag (creating pressure on the
fan) in your vacuum cleaner gets plugged. Not much air flow going in then.
Confusion occurs I think because people think about things like there
furnace or a linear with forced air cooling. There are blowers that ARE
designed to work against positive pressure. Squirrel cage blowers for
example. In this case, the blower is able to pressurize the enclosure
and the warm air is expelled thru vents in the box. The fundamental
design of the blower is different.
In fact, small fans can't operate very well with much suction either but
really die with pressure. They are designed to operate in a moving
stream of air. Restrict the stream, and efficiency drops drastically.
The AC4 is really a excellent setup for cooling. The slots around the
cover low and high offer a fair amount of total cross section open area,
and when the fan draws air out of the box, the ingoing fresh air is
distributed thruout the enclosure and exhausted via the fan. No dead
air and constant, low level flow.
A great setup would be the fan exausting from one end and inlet holes in
the opposite end. I looked at doing that but then the PS would not fit
inside the MS4.
Across Yaesu, ICOM, and the Drake TR7, ALL of the fans, standard and
optional, draw air out of the enclosures. This maximizes the efficiency
of the fan operation, reduces the chance of dead air hot spots.
So..I am staying with my approach to utilize fans on all of my drake and
other equipment..I'll have the R-4 fan install pix added soon to the
picture album..as noted before, it keeps the r4 audio tube heat from the
transformer and in the process, improved the initial vfo drift
performance as well.
Will the AC4 drop dead without a fan? No, surely not. Will it last
longer with one? Absolutely.
In the interest of closure, I will post this to Drakelist as well Damien.
As always, questions or comments are welcomed.
Curt
KU8L
Damien Mannix wrote:
Been following this thread with great interest. Thanks guys.
I do not understand the dynamics but am anxious to learn. Do I gather
that it is important to extract air from the AC4 rather than blow air
into, or through, it?
Damien
C6AXE
> Date: Wed, 15 Dec 2010 19:22:01 -0500
> From: [email protected]
> CC: [email protected]
> Subject: Re: [Drakelist] AC4 heat
>
> Well..you guys can suit yourselves but...
>
> Did the AC4 just sit there running filaments or were you running it
with
> a 50% key-down 300ma load on it for hours on end?
>
> Ask the RTTY contest guys how warm they get.
>
> Sure they stay cooler outside the MS4. Cool enough? Having serviced
> commercial, amateur and industrial electronics for over 40 years, I can
> tell you, without hesitation, that the cooler this stuff runs, the
> longer it will last.
>
> BTW..I have owned an original AC4 since 1966 and it is still fine. I
> have replaced the guts with one of the upgrade boards but think the
cost
> of fan is good insurance so I never have to find out how long they will
> actually last.
>
> Also BTW...anyone that suggests that you blow air INTO a box to cool it
> does not understand the dynamics of the problem.
>
> My original T4x is also still fine, but I put a fan on the final
cage of
> that unit. Lets see...a pair of finals cost a little less than a power
> transformer last time I checked.
>
> Suit yourselves..
>
> Curt
> KU8L
>
>
>
>
>
>
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