[Amps] soft-start vs. autotransformer

[Tom W8JI]

> I turned the autotransformer to show a reading of 2400 VDC 
> on the equally high-accuracy Heathkit meter, and then set 
> the exciter to give an output of about 650 watts on my 
> Autek wattmeter.  The HV sagged to about 1900 VDC.  The AC 
> ammeter reads about 7 amps as the output stays steady.
>
> Is there further information I should supply to determine 
> if things are OK?  Is the problem only while I turn up the 
> autotransformer, in other words, am I still getting 
> damaging inrush current?

Hi Jan,

What is the full load HV on the SB 200 with the amp plugged 
directly into the outlet, and with the amp plugged through 
the variac system to the same outlet, when you are running 
the same plate current and have the same starting voltage?

This will tell you how much if any the variac reduces 
regulation.

If it doesn't change loaded HV at the same plate current and 
same starting voltage then the variac is doing no harm when 
set to that voltage.

Another interesting test would be to see what the difference 
in % regulation is with the same input power (plate voltage 
times plate current) at reduced HV.

I've seen good variacs and bad variacs.

73 Tom