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Re: [Amps] SB 220 Exploding Resistor

To: "Tom Hellem" <>, <>
Subject: Re: [Amps] SB 220 Exploding Resistor
From: "Jim W7RY" <>
Reply-to: Jim W7RY <>
Date: Sun, 17 Jan 2016 21:35:25 -0800
List-post: <">>
You either had (momentary arc) or have a shorted tube.

Be careful with the way the bias on the relay is wired. If the cathode shorts to ground, you can burn up the filament transformer by shorting out the 120 VDC bias circuit.

Replacing the small VHF choke with a 10 ohm 10 watt wire wound resistor is common practice.

Bottom line.. You probably have a shorted tube.

Jim W7RY

-----Original Message----- From: Tom Hellem
Sent: Sunday, January 17, 2016 8:05 AM
Subject: [Amps] SB 220 Exploding Resistor

My SB 220 has what appears to be a glass coated wirewound resistor in
series with the anode B+
supply lead just before the RF chokes. It is not on the schematic so must
have been a modification
done at some point. It blew up in spectacular fashion one day and I
hesitate to just replace it without
having some idea of what may have been the root cause. I do not have much
of an electronics background
and would appreciate if someone could suggest some things that I should
check out before I try to put it
back on line.

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