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Re: [Amps] SB220 running plate current when no drive; Problem found

To: amps@contesting.com
Subject: Re: [Amps] SB220 running plate current when no drive; Problem found
From: Jim <jimw7ry@gmail.com>
Date: Tue, 6 Oct 2020 12:23:49 -0500
List-post: <mailto:amps@contesting.com>
What brand is the defective tube?  What is the date code?

Thanks

Thanks
73
Jim W7RY

On 10/5/2020 9:28 PM, Steve AA7V wrote:
Hello to the group;
First, thanks to the many folks that took the time to answer my inquiry.
Your responses are greatly appreciated.
Second, I removed one of the tubes, powered on the amp and the behavior
seen before was gone. I found and installed a spare and now the amp is back
to normal ops.

The faulty tube is 6 years old. I dont know what the normal life-span is
for a 3-500z but I had hoped for a few more years.

73 to all
Steve AA7V



On Mon, Oct 5, 2020 at 11:03 AM Steve AA7V <aa7victor@gmail.com> wrote:

Hello to the group;

My SB220 has started to act up.

Immediately upon power on, the 3-500s both start drawing plate current.
The meter shows approximately 250 ma of current. It is apparent some
component has failed.

Also, it appears the grid current meter is showing a negative value (if
this is possible) as the needle now rests on the left peg.

I am not adverse to troubleshooting to the component level but would
appreciate any advice as to how to narrow my search to a specific set of
probable causes.

If I am unable to fix this amp, does anyone have any recommendations
towards a person that works on SB220s?

Regards

Steve AA7V

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