[AMRadio] Step Start

Brett gazdzinski brett.gazdzinski at verizonbusiness.com
Mon Dec 11 12:37:18 EST 2006

> I plan to reroute the hi/low switch to a resistor or better 
> yet a light 
> bulb to reduce in input voltage at start up.

Light bulb wont do, too high a resistance.
Some used those old ceramic heating elements that were used in
very old fashioned space heaters, looked like satellite dishes
sort of...

> The original was limited to 110v but with a resistor, I can 
> provide any 
> start up voltage I want so I need some help figuring out what 
> resistance 
> would be best.

I would guess around 5 to 10 ohms, more on the 5 ohm side.
Too high and you will get only 100 volts in the 1/2 second
of step start. You want about 1/2 voltage...

> There is a time delay relay that precludes putting any voltage on the 
> primary for one minute to allow the tubes to warm up so I presume the 
> hi/lo is to reduce the surge upon charging up the caps.

That time delay is for the mercury vapor rectifiers.
I use solid state diodes (1 amp at 14kv), less muss and fuss...

> 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.

Not much average power, but on step start peak currents are high,
even with choke input. Make the step start resistor 25 or better watts.
The step start resistor only comes into play for the 1/2 second during
step start, the time delay relay should them short it out.
If you want a 1/2 voltage tune position, then the resistor has
 got to be a good size...

> Thoughts please.
> js
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