[Amps] Step start, is it needed ?

[Jim Thomson]

Date: Tue, 23 Feb 2010 08:18:40 -0800
From: Vic K2VCO <vic at rakefet.com>
Subject: Re: [Amps] Step Start circuit - needed or not?

The SB-1000 does not require a step-start. The transformer is designed so that the 
secondaries have enough impedance to protect the diodes and tube filament at startup. It 
also has a relay to protect the switch (at least mine, which is a late model, does).

##  anybody that designs sec windings on plate xmfr's to be high Z these days,
just to eliminate the start up surge, needs to go back to school.  If it goes off with
a helluva thump, on turn on.. you need step start.  That thumping is hard on the
on/off switch, caps, diodes, and xfmr itself.   If he ever changes out the caps  to 
larger value ones some day, he will need step start anyway, so he may as well 
install it now, and be done with it. 

##  High Z  sec windings on plate xfmr's is just a cheap way to wind a plate xfmr,
and enhance profits. [read small ga wire]    Ditto  with Ameritron leaving out the glitch
R for years on end. Reasoning was, each  of the 8 x lytic's  had 1 ohm esr.. + another
2 ohms in the plate choke = 10 ohms esr... = no glitch needed.   That doesn't cut it 
these days.  My last bunch of small caps  measure .017 ohm esr... each.   So newer 
caps are not only higher uf, they are also lower ESR.  new ones WILL thump, and then
some. 

later....... Jim  VE7RF 





Having said all that, I added a step-start to mine to eliminate the thump that it 
sometimes emits on startup. But I think that's only an aesthetic thing.