[Amps] resistor before the cap redux

[Jim Thomson]

 I just ran a bunch of numbers on PSU designer and got quite different
numbers than yours. I suspect it is because of the way measurements are
being made. That is if I am doing things right here!
 


Notice that with the 10 MFd filter and 22 ohm series resistor the Vo
Drops 387 (multiplied by 100) volts from 267 ma load to 1.64 amp load.
With a 100 MFD capacitor that voltage drop is only 149 volts.

With no series resistor and a 10 MFD filter the voltage swing is 377
volts. Only 10 volts better than with the 22 ohm resistor.

But with the 100 MFD filter the voltage swing from 272 ma to 1.82 amps
is only 59 volts without the 22 ohm resistor. This is about 100 volts
better regulation than with the 22 ohm resistor.


Should we not worry so much about low resistance windings on our
transformers?

###  Low resistance winding's on a plate xfmr are everything imo. 
A buddy just went through grief, using a NEW 46 lb mag cap xfmr
for a 6m  gs35b 6m amp.    V regulation was terrible.  Sure, there
was a 6 v  drop on the long 12 ga  240 line... but that same line
power's  his alpha too. [ not at the same time of course].  700 v drop
on the single tube 6m amp.  

## The mag cap was changed out  with a huge dahl xfmr,
complete  with 2 ga  wire back to main panel  and a string of 
2500 uf new HV lytics.  NOW, the V regulation is superb.  
Less  than 150 v.  

##  I call the B+  voltage you get, when drawing ZSAC, the real
NO load B+...  not  when on RX.   Amp has to idle 1st... b4
drive can be applied.  [assuming NO EBS]  OK, hit the PTT, and
either pulse tune..or talk on ssb.     B+ barely moves.  PEP  out 
of the amp is WAY up.

###  Installing the 20-25 ohm resistor between  FWB  and B+ caps
would have one good application though.... for step start.  In that case,
you don't have the problem of PRI magnetizing current  flowing through
the normal ..'resistor in one leg of 240 line'  conventional step start. 

## the mag  current on some of my 4800 vac pole pigs is 1.9A 
IE: you can never fully charge the B+ caps  up to almost full. I end up
with one helluva big sec surge, when resistor in 240 line is shorted. The
fix for now, was to reduce it's value.  [25 ohms..down to 10 ohms] 

## Now, installing the  25 ohm resistor, between FWB  and B+ caps..
this would be great  for step start...THEN, short it out  with a VAC
relay !!    Caps  will charge right  up to max B+ 

###  Then, with vac relay present,  it's  a snap to toggle between..."22
ohm resistor in line.. or OUT  of line"     I haven't tried the vac relay part
..yet.... but did install a 25 ohm, 225 watt, WW  between  FWB..and
B+ caps.... and V regulation goes to hell..fast.  The bigger the load,
the worse it gets.  Which is exactly what PSUD  predicts. 

## The test is repeatable.   Try it yourself [with a big load... like
either key down  1.5 kw out cxr... OR... just plane SSB.]  It's lousy
either mode..with that 25 ohm resistor installed.  

later.... Jim  VE7RF 





 
Hope all the columns line up.

73
Gary  K4FMX