[Amps] SB220 step start blows fuses

gudguyham at aol.com gudguyham at aol.com
Thu Jul 6 05:12:38 EDT 2017

If you have the HV transformer disconnected as you said you added a Molex disconnect, and if you have the amp set for 240 instead of 120v, the fan should not turn with the transformer disconnected, unless you just disconnected the secondary from the rectifier.  In this case it might indicate a miss wiring.
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-----Original Message-----
From: Warren Volz <warren at warrenvolz.com>
To: amps <amps at contesting.com>
Sent: Thu, Jul 6, 2017 03:11 AM
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?

Also, would these steps (or something similar) make sense?

1) Re-enable HV supply, power on, if fuses are ok power off and go to step 2
2) Once HV dissipates, add tube 1, if fuses are ok, power off and go to step 3
3) Assume tube 2 is shorted, else tube 1 is bad

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