[Top] [All Lists]

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

To:, Steve AA7V <>
Subject: Re: [Amps] SB220 running plate current when no drive; Problem found
From: Donald Fox via Amps <>
Reply-to: Donald Fox <>
Date: Tue, 6 Oct 2020 02:49:44 +0000 (UTC)
List-post: <>
Glad to hear you got it figured out in short order. If only the majority of 
repairs in amplifiers were as easy as this one. Thankfully, the tried and true 
3-500s are still in production, and not for an arm/leg.

The forum here seems to be a faint example of what it once was. I hope everyone 
I am used to seeing here is well, and still enjoying the hobby.


     On Monday, October 5, 2020, 10:32:42 PM EDT, 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 <> 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
Amps mailing list
Amps mailing list

<Prev in Thread] Current Thread [Next in Thread>