[Amps] SB220 step start blows fuses

Jim Thomson jim.thom at telus.net
Wed Jul 12 01:05:16 EDT 2017

Date: Tue, 11 Jul 2017 08:16:20 -0700
From: "Jim Thomson" <jim.thom at telus.net>
To: <amps at contesting.com>
Subject: [Amps] SB220 step start blows fuses

< On  a side note, if the step start is done correctly, and step start resistor inserted into one
<leg of the 240 vac primary..... or hot leg if wired for 120 vac,   you will be able to step start the HV supply and both fils...simultaneously. 

<Jim  VE7RF 

##  I used  a single 25 ohm resistor in one leg of the 240 vac line...for my hb, external step start setup, for my drake L4B amps. 
That value  works out really good.   Allows the B+  to ramp up  to aprx 2480 vdc....and both 3-500Zs fils run at aprx   87% of full
brilliance.   Once the 25 ohm step start resistor is shorted out, the  2480 vdc  jumps to  2650 vdc.   Both tube fils  are then at full
brilliance.   Both B+   and fils are step started simultaneously.   I have used that system for several years now. 

Jim   VE7RF   

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