I cured mine by changing the fan to the Papst 8412NGL
Quiet Case Fan 12dB I bought from endpcnoise.com
I further put 6 diodes (1n4001) in series with the +
lead and short them out with a PNP transistor
(2n2907). The emitter of the transistor goes to the
V+ The collector to the other end of the diode
string. The base is switched to ground through a 1k
resistor. I attached a wire to the PIO board pin #6
where the X2 socket connects to the board, and turn
that pin on in the software during transmit. The fan
is dead quiet during RX and turns on to its full
power, which is still very quiet with the Papst fan
with transmit. I have noticed no freq stability
problems. I run full power to drive my amp, and it
works fine.
I hope the description makes sense
It goes something like
V+ -->|-->|-->|-->|-->|-->|-- +|fan|- ---gnd
The emitter goes to V+ the collector goes to the
junction between the last diode and +fan and the base
goes to pin 6 on X2 through a 1K resistor.
The parts (except the fan) are readily available from
radio shack. You have to replace the screws that hold
the fan with screws that are 1/4" longer since the fan
is 25mm and not 15mm, but it clears the PA heatsink
just fine.
If you just want to tone down the fan that comes with
the SRD-1000 you can just add the diodes and
transistor. You can tap the emitter of the transistor
anywhere along the diode string and it will give you 2
speeds with the higher speed being a lower than max.
I built mine on a piece of perf board, and have a
stiff piece of #14 solid that goes to the - fan lead
on the terminal strip strip in the radio. It supports
the board without any further support needed. A
flexible wire goes from the board to the V+ terminal.
This was the cheapest and simplest solution. I
considered using a 555 one shot with a longer timeout
but I think its not really necessary and the parts
count goes up by another 7 parts.
If I was running 100W rtty or AM, I would just turn on
pin 6 in the RX portion of the X2 menu and you would
get the default full on fan speed.
73 W9OY
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