[Hallicrafters] Hallicrafters SR400A fan

[David Yost]

Don:

I also have an SR400A that had a very noisy fan. I tried replacing it 
with another 120v "whisper fan" but it was even worse. I picked up a 12 
volt DC 80mm computer fan at a local surplus outlet (Electronic Surplus, 
Cleveland).  I then built a simple DC power circuit in the power supply 
to power it. It is virtually inaudible now and moves plenty of air.

I also recommend mounting the fan using small rubber grommets as washers 
to dampen vibration transmission to the case.

For the fan power supply, I used a 1N4001 diode, a 2000 uf cap to 
ground, and a 400 ohm ww  resistor in series with the diode to drop the 
voltage to 9 volts (lower rpm, quieter fan).   The diode is fed by the 
12.6 V filament line.

73
David Yost
WA8UFZ