This bracket is made from 0.062" aluminum and is made to accept two 2.36" (60mm) AC or DC fans and their wire fanguards.
The article for this bracket appeared in the Mar.'95, Issue #71, Electric Radio.
The photos above show a typical installation of the bracket using two NMB Model 2412PS-12W-B30 115 Vac fans into a KWM-2. Wired in series for 230 VAC or parallel for 115 VAC.
No modifications are required to either a 32S-( ) or KWM-2. The option drops in. It mounts using the three existing screws in the 6146 xmtr cage.
The use of the NMB fans lowered the internal temperature by 20 degrees C and decreased the warm-up frequency drift. If you find the AC fans to be generating excessive
noise in the shack, you may wish to try using a variac or light dimmer to slow the fan speed. Alternately, when using DC fans,
a lower fan speed reduces the noise while maintaining an air flow. I also use a small AC muffin fan mounted on rubber bumpers
that sits on top of the case and is portable from unit to unit. Either way it is beneficial to provide
air flow through your equipment. An idea from Doug WB7TUJ : He has two 12 VDC 4" muffin fans, one over the PA cage of his KWM2-A & one
over the 811A's in his 30L-1. He runs them both from the 516F2's filament supply and an external bridge rectifier. He dosn't use a voltage doubler and
has 100mf across the output of the bridge. The lower DC voltage (8VDC) lets the fans run very quietly, yet they do move a lot of air. He pulls the air up &
out of the cabinets.
An idea from Rich WB3JLK : A fan for your KWM-2 will do nothing but help the rig. A lot of heat,
especially in the PA compartment builds up in a relatively small
space. Getting that heat out extends component life. My suggestion and
this is based on a KWM-2 that I saw while visiting W0CXX in Cedar Rapids
is to mount a fan to exhaust air above the PA compartment. Use a couple
nylon 4-40 screws and bolt the fan to the hinged cover. Then by building a
voltage doubler with 2 diodes and two caps, you can use the rig's 6.3
volt filament line to run a 12VDC fan. You can steal the power from the
socket for external vfo power.
I use the fans manufactured by a company called Innovative, Model
BP802512H. They are DC brushless fans and consume 12V at 0.2A. They can be
found at RadioShack.com stores. I'm not sure what the regular Radio Shack
stores carry, but I generally find their components substandard. John May
I am powering them off the 6VAC output found on the back of the KWM-2. Make
sure you use a bridge rectifier with a 100uF filter cap (these are DC Fans).
The fans, bridge rectifier, and filter capacitor are all mounted on the
bracket described above. Because the fans are 12VDC and I'm running them off
8.9VDC (6.3VAC filtered) they run a bit slower (and quieter). They keep my
KWM-2 plenty cool.
I did meet someone at a hamfest who simply placed the fans on top of the KWM-2
(over the final amp cage) and claims that it kept the finals so cool that they
no longer achieved thermionic emission. Sounds like an urban legend to me (or
that his 6146's need replacing).
