[Amps] Step Start on a 3KA Amp

Gudguyham at aol.com Gudguyham at aol.com
Mon Sep 18 00:04:20 EDT 2006


 
In a message dated 9/17/2006 11:24:51 P.M. Eastern Standard Time,  
bmaser at tampabay.rr.com writes:

Can  anyone tell me what good is it to have one of those cone heaters in 
series  with the primary of the plate transformer?  When the cone heater is  
in the circuit, the secondary voltage is 2800VDC and when it is shorted  out, 
it is 3000VDC.  Hardly seems worth the effort.  The cold  resistance of the 
cone is ±30 ohms.

Bob  W6TR  



Bob, the initial start up voltage drop across  the resistor is  enough to 
soft start the power supply so it does not BANG and cause undue stress  on the PS 
components.  Though you do not see what it actually does voltage  wise, it is 
in fact softening the start up as it is intended.  Usually a  resistor is 
used in the order of 10-25 ohms, this amp opted for the cone  resistance which 
does the job well and will handle a lot of heat.  I guess  if you looked at the 
ramp up of the HV on a scope you would see a big difference  between using the 
cone and not.  You just can't see it well enough on the  meter.  Lou


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