[Amps] SB220 step start blows fuses

Jim Thomson jim.thom at telus.net
Tue Jul 11 10:39:39 EDT 2017

Date: Thu, 6 Jul 2017 00:07:50 -0600
From: Warren Volz <warren at warrenvolz.com>
To: amps <amps at contesting.com>
Subject: Re: [Amps] SB220 step start blows fuses

Thank you for the flood of good suggestions. I'm getting closer.

Without tubes and with the HV transformer unplugged, the fan and meter lights work. In addition, the step-start fuses don?t blow!

That leads me to suspect the tubes + HV supply. I checked the windings on the HV transformer to look for shorts:

BLK-YEL = .7 Ohm
BLKGRN - BLU = .8 Ohm
BLU - BLKRED = 0 Ohm

Do any of those look off?

##  Yes,  I already mentioned this b4 !   You should be seeing 9-10 ohms
across the plate xfmr sec...with  plate xfmr sec NOT connected to the diode board. 

##  IF the diodes in the diode board fail, they typ fail shorted.   If you still
have the diode board connected to the plate xfmr secondary,  you will also
see  close to 0 ohms across the plate xfmr sec. 

Jim   VE7RF 

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