[Johnson] Desk KW fan update

[Rodger]

After a number of very helpful suggestions from the list regarding my 
fan issue I finally decided that the best course for me was to make a 
bit of a change to the cooling system.  In place of the internal fans I 
mounted a pair of Comair Patriot fans to the intake and exhaust 
positions on the back of the pedestal.  Although I generally avoid 
drilling any holes in equipment I can safely say that my Desk KW won't 
be sold until I am a silent key and at that point I don't think my wife 
and daughter are going to be dependent upon the proceeds from the sale 
of a single piece of gear (and at age 48 hopefully that is a long time 
in the future).  So with some trepidation I drilled 6 small holes in the 
back for the fan mounting screws and I used thin foam weather stripping 
between the fan housing and the fan for an air seal and to reduce noise 
and vibration transmitted to the pedestal case.  Of course in normal 
operation the fans are invisible anyway.  To power the fans I inserted a 
multiple output plug in the back of the Desk where the Ranger normally 
plugs in by itself.

The Comair fans are capable of moving a lot more air than the stock 
units and since they seal to the openings they provide a very positive 
flow of fresh air in and heated air out.  With the extra air capacity I 
was able to add an air filter (standard Comair accessory) to the intake 
fan.  Over the course of a year the bottom fan had drawn quite a bit of 
dust into my Desk KW and the fan which cools the bases of the 4-400A 
tubes had also built up a bit of dust on its screen; there is no real 
air filtering of the intake air in the stock configuration.  I also used 
a Variac to reduce the voltage to the new fans to further reduce the 
noise and running at just over half their rated voltage there is 
noticeably more air flow from the exhaust vent and after a couple of 
hours of testing into a dummy load the pedestal was noticeably cooler 
with the new fans.  I am sure I could run the fans at even lower voltage 
and have plenty of cooling but they are already quieter than the stock 
units so I will stay with the present setting.  I originally tried to 
use solid state fan motor controllers but even with noise filtering they 
generated noticeable QRN in my quiet rural setting.  The capacitor type 
speed switches sold for ceiling fans would probably work but they don't 
give the range of control my Variac does and I had a number of small 
Variacs on hand.

So, this isn't the solution for everyone but it was the one I decided 
was best for me.  I now have a spare motor in case one of the two fans 
inside the RF deck goes out.  The Comair fans I used are dual ball 
bearing units and are very nicely constructed. 

Again thanks to everyone for their suggestions and offers of help.  My 
Ranger, Desk KW, Hallicrafters SX-88 station is now back in full 
operation.  While the Desk was down my Viking 500 got a lot of use and I 
need to hook the 500 back up to its normal receiver (a Pierson KP-81) 
since it also recently needed some attention.  The receiver failure was 
due to a shorted mica cap which wouldn't be unusual except that the 
failed unit was a brand new production unit installed when I restored 
the receiver a couple of years ago. 

Best wishes to all,
Rodger WQ9E

 Rodger wrote:
> Good morning all,
>
> The lower pedestal fan in my Desk KW developed a short in the winding 
> and went up in smoke.  Has anyone come across a source of replacement 
> fan motors for these?  I cannot find any identification anywhere on 
> the fan assembly as to maker, RPM, etc.  I suppose I could have the 
> coil rewound but the bearings probably should also be replaced so if I 
> could find a source I would like to find a new replacement.  Any 
> advice and/or leads appreciated.  By the way, when the fan motor goes 
> it really develops a lot of smoke and smell.  It made me realize that 
> if something catches on fire inside the pedestal it could be a big 
> problem.  I do have the main shutoff switch for the 240 volt feed 
> nearby and I guess there isn't a lot that would really burn well 
> inside the pedestal but given this experience I am only using one of 
> the two thumbscrews to secure the cage inside the pedestal and a fire 
> extinguisher is in one of the desk drawers.
>
> I am probably being paranoid after this experience but if I were 
> really paranoid I would be investigating an on-board halon system :)
>
> 73, Rodger WQ9E
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