[NJARC] BC-348Q Power Questions - Sanity Check

[Scott Roberts]

Ok. I will be the first to admit I know very little
about electricity. Other than the quick course I had
in A&P mechanics, I have had no formal training. And
that was over a year ago... I try to look up stuff
first, and apply the formulas I half remember, but I
am still struggling. Once the discussion gets
electro-technical, I  struggle a little. I will be
getting better at this, but it will take a while.

I have my power supply for the BC-348 together. First
the good news- the 24VAC supply for the heaters is
putting out the right voltage. 

The main transformer is putting out about 500VAC, with
250 coming out the tap. The two 500V lines are passed
through a pair of 1N4007 diodes for rectification. At
this point, I get around 250VDC The B+ line then
connects to a 47/450 electrolytic(to B-), then a
filter, then a pair of 22/450 Electrolytics(in
parallel with each other for 44/450)(to B-) then out.
At this point, I am getting 330VDC.

So I tried clipping in a bleed resistor between B+ and
B-.  I tried a 125 ohm resistor, and power dropped
below 200VDC. So I tried a smaller resistor, and the
voltage dropped further! This surprised me, but
thinking it over, it is starting to make some sense.
The less resistance, the more return, so lower
voltage. I finally got the voltage to the right spot-
by clipping 5-500ohm resistors in series, for 2500ohms
total. The resistors I am using for this test are
marked "Dale RS-10 500ohm Mexico" and are about 5/16"
dia. by two inches. The specifications I found online
state:  RS-10 
    * Wirewound Resistor
    * Series:RS
    * Resistance:500 ohm
    * Resistance Tolerance:+/- 1 %
    * Power Rating:10W
    * Resistor Element Material:Ceramic
    * Temperature Coefficient:+/-90 ppm
    * Leaded Process Compatible:No
    
Would these resistors, placed in series and parallel
to the electrolytics, be acceptable to drop the
voltage during use? I imagine a 10W wirewound would be
adequate...

Scott


__________________________________________________
Do You Yahoo!?
Tired of spam?  Yahoo! Mail has the best spam protection around 
http://mail.yahoo.com