[R-390] Fan Power Supply Voltage and RTTY Question

[Al Solway]

"Scott, Barry (Clyde B)" wrote:
> 
> List,
> 
> Power Supply question:
> I built a simple power supply to drive a cooling fan for my R390A.  I used an 18VCT in a "double half wave" rectifier configuration (the same way the R390A HV power supply is done).  I slapped a cap across the output (20mfd as I recall) and it was delivering a clean 14VDC no-load voltage on the scope.  Fine, I thought.  Good enough to drive some small fans.
> 
> Well, when I connect the fan, the voltage drops to about 9 volts (according to the DVM).  The fan is drawing about 120ma.  What causes the sudden voltage drop?  I need to look at the voltage on the scope, but I suspect the cap is discharged through the load between half cycles and the DVM "sees" 9VDC when, in fact, it is a rippled DC signal.  Does this sound plausible?
> 


Scott and List,

I have installed a fan in my R-390A and plan to do so for the R-390 when
the restoration is complete. I used one of those toy power
suplies/chargers that plug into the wall, rated at 9VDC 300MA. The fan
is 2.75 inch, 12VDC, 120MA. The P/S is mounted underneath, to the rear
and to the left of the PTO. I used a large tie wrap about 3/8 inch wide
cut to length. Holes were drilled in it. The screws that secure the
partition between the PTO and the Audio chassis were used to support the
P/S. I soldered  wires to the AC plug on the P/S. The other ends of the
wires are soldered to the AC input. I do not use the Function Switch to
turn on power. The AC is switched externally. The DC O/P is connected to
the fan with a small connector. Never did measure the DC O/P under fan
load but the fan cools the radio very well and runs quiet. The fan has
been running for 10 months about 10 hrs/day. 

Al