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Re: [Amps] SB220 step start blows fuses

To:,Warren Volz <>
Subject: Re: [Amps] SB220 step start blows fuses
From: Victor Rosenthal <>
Date: Mon, 26 Jun 2017 12:31:15 +0300
List-post: <>
I would certainly check the filter caps and diodes. You can try the amp without 
tubes to establish that the problem is in the power supply.
The filament to grid shorts I've seen in 3-500Zs have only showed up when the 
filament were hot.
Vic 4X6GP

On June 26, 2017 8:54:00 AM GMT+03:00, Warren Volz <> 
>I’ve been restoring a SB220 and finally got to the testing stage this
>weekend. When I turned it on, the HV went up to ~1kV and then started
>to drop. Successive cycles of the power switch did nothing. Oddly, the
>meter lights and fan never started running. I looked at the bottom of
>the amp tonight and the 3A fuses I added to the W7RY step start board
>blew. What areas should I look at now to determine what is going wrong?
>I have both tubes in, and I believe I previously checked them for
>filament shorts. I’m worried the HV supply has an issue.
>Any advice would be very much appreciated!
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