[AMRadio] Step Start


D. Chester k4kyv at charter.net
Tue Dec 12 13:06:35 EST 2006


> This is a choke input with two 4 mf in parallel across the output and 
> somewhere it seemed to imply that the step start was only needed for cap 
> input.
>
> As far as I can get with the heavy math, it seems like the resistor 
> required would only be a few watts as it is only dealing with the 100k 
> bleeder as a load.
>

I'm not sure how much plate voltage and current you plan to run from the 
power supply, but it has been my experience with loads on the order of 
2000-2500 volts at 600-700 mills or so, you don't have to worry about the 
need for step-start with choke input filter using a swinging choke, until 
you go beyond 25 mfd of filter capacitance.

My 8005 rig runs at 1300 volts on the plate, with total drain from final, 
modulator and audio driver  plus bleeder resistor, somewhere in the vicinity 
of 700-800 mills.  I use a 52 mfd filter with no step start without a 
problem.  The filter choke in that rig is non-swinging, 10 Henries @ 1 amp. 
The p-p 845 audio driver stage stays on all the time and pulls about 150 
mills, acting as extra bleeder, holding the voltage steady even for cw 
operation.  Add the steady 320 ma drain from the final during AM operation, 
and the plate voltage is very stable during modulation, which keeps the 
class-B modulator stage happy.

Don k4kyv 




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