[R-390] AF Deck recap

[rbethman]

It sounds like someone "may" have put it in with the polarity reversed?

That would make life get interesting!

It "could" perhaps take out the fuse.  Being it is so small, it wouldn't 
have made a bang.

Bob - N0DGN

On 1/9/2012 11:14 AM, 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
>
>
> Copyright (c) 2012.  Not for redistribution
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