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Re: [Amps] SB220 step start blows fuses

Subject: Re: [Amps] SB220 step start blows fuses
From: Geert Jan de Groot <>
Date: Sun, 23 Jul 2017 23:23:20 +0200
List-post: <>
Sorry for raking up an older topic; I don't always have time
to keep up with mail.

In the whole discussion, what I did not see is that the
power supply of the SB220 is lineair.
I have used this to my advantage by, instead of putting
line voltage on, ue a much smaller AC voltage (a few volts)
on the AC input and then measure how the circuit behaves itself.

If the thing is wired for 220V, and instead of powering with 220V
one powers with 5V AC in the primary, then the secondary circuit
works except that instead of messing with 2000V, one now works with
50V on the HV circuit. That is plenty to test diodes, measure caps etc,
and it's a while lot less nerving.

One has to realize that the filaments of the tubes will represent
a dead short (5V, 15A when in operation; cold resistance is less)
but I found this to be a lot less nerve wrecking and a lot safer 
than trying to put line voltage on, with or without lamp,
with or without variac

One can measure circuits running at just a few volts; wiring errors,
dead shorts etc will show much easier and without pyrotechnics.

Of course it is possible that a component works on low voltage
but fails on full voltage, but being able to "dry run" has helped me
a lot to get my SB220 back in working order.

Just a thought,

73, Geert Jan PE1HZG

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