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

[Jim]

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 at 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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