[R-390] AF Deck recap

[Renee K6FSB]

hi Don-
I thought a 5814A was a 12AU7A only matched with sections and 
reliability....maybe I am in error?
Renée, K6FSB

2002tii wrote:
> Dave wrote:
>
>   
>> Over the weekend I have been working on bringing one of my R-390a's back
>> to life. Had not used it in a long time, when I did it blew the fuse. So
>> turns out that the filter caps were bad, so I decieded to recap the
>> whole deck. After I was done, placed it back in the radio and played for
>> an hour or so, then the fuse poped, turned out that C609 which I just
>> replaced is bad, I put the original back in and again it plays just
>> fine. When I re-capped I used a 10uF 35V tantalum from mouser part
>> number 74-173D106X9035XE3. *Looks like I used the correct part. So what
>> gives? Just a bad new part? or am I over looking something???*
>>     
>
> I do not think you have found what caused the fuse to blow.  C609 is 
> just the bypass cap on the cathode of the first audio amp (V601A, 
> half of a 5814A a/k/a 12AT7A).  Any current that flows through C609 
> has to flow also through V601A and its 56k plate resistor, 
> R605.  Even if the tube and the cap were *both* shorted (0 ohms), 
> they could only draw around 5 mA from the B+ line through R605 (which 
> is only about double the stage's normal operating current) -- nowhere 
> near enough to blow the fuse.
>
> Best regards,
>
> Don
>
>
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