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G8MNY  > TECH     18.08.18 08:45l 64 Lines 2520 Bytes #8 (0) @ WW
BID : 34129_GB7CIP
Subj: Variable Speed Thermal Fan
Sent: 180818/0633Z @:GB7CIP.#32.GBR.EURO #:34129 [Caterham Surrey GBR]

By G8MNY                                   (Updated Jul 15)
(8 Bit ASCII graphics use code page 437 or 850, Terminal Font)

I have often been annoyed by fan noise from over powerful fans in gear. Here is
a solution I adopted for a 12V PSUs & 400W HF PAs. Small 12V fans can be found
in a scrap PCs etc & draw about 70-100mA depending on speed & size.

2x PNP CIRCUIT (Germanium NPN can be used E-C reversed)
   use idiot diode & fuse if fan manually wired up.
   旼컴컴컴컴컴컴컴컴컴컴<쳐o-o컴 +12V
  PNP쳐커                                                 FANS
    /  e\쿛NP Small                           旼컴컴컴컴컴컫컴컴컴컴컴컴
          Germanium              Sponge fill         Tab~           
        /쿫etween fins            gap so fan..읕컴컴컴컴컴탠탠컴컴컴컴컴.
   쳐컴켸                          blades kept       頻      
  __                              away from         殯      
 / + \  For a quieter fan,         fins for    栢栢栢栢栢栢栢栢栢栢栢栢栢
 12V  try 2 in series,           min noise.                           
 \FAN/  or use a 24V one!                           P A   /   P S U     
   읕컴컴컴컴컴컴컴컴컴컴컴컴컴컴 0V          읕컴컴컴컴컴컴컴컴컴컴컴컴
It uses a high gain (x100) tab silicon NPN or PNP controlled by a leaky
Germanium PNP or NPN placed between the hot heatsink fins (test a germanium
with a soldering iron for resistance change & Fans on/off). I used an all
plasic Tab silicon cable tied to the fans, with the insulated geramanium
transistor E & C leads twisted (make sure it's case is isolated or insulate) &
exposed connections in heat shrink etc.

Fan operation is typically from @ 50C with a slow variable speed action until

The fan can be in the earth path or +12V side...

Silicon NPN & Germanium PNP CIRCUIT
   旼컴컴컴컴컴컴컴컴컴컴<쳐o-o컴 +12V
 / + \  For a quieter fan,
 12V  try using 2 in series,
 \FAN/  or use a 24V one!
       e\쿛NP Small
    \   /쿫etweens fins
   읕컴컴컴컴컴컴컴컴컴컴컴컴컴컴 0V

In high use (waffle mode with processing on or a pile up) the fan starts up &
runs very quietly from about 5V across it, & gently runs faster if the heatsink
gets hotter.

See TECH bul "PA & PSU Fan Noise"

Why Don't U send an interesting bul?

73 De John, G8MNY @ GB7CIP

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