[AMRadio] [Boatanchors] 100TH and 250TH advice and or comment


rbethman rbethman at comcast.net
Tue Aug 25 15:09:57 EDT 2009


Dave,

I was looking at the PA stage in particular at the time.

Mostly I had on just filament.  I suspect that these triodes, even on 
just filament, probably need a muffin fan or some such, even though 
Uncle Sam ran these without any cooling.

I say this because I've got one 250TH sitting in a socket on the shelf.  
It has about half of the hours of this radio that *I* have put on it.  
It is as clear as can be.  It looks like THEY ARE GASSY!  No question.  
I'm also trying to get to the mechanism.

We know the 4-XXX and up series REQUIRE filament cooling.  I'm beginning 
to think that the triodes need this too!

Bob - N0DGN

David Hollander wrote:
> I have done filament testing in the past year on a large number of 
> 813's that were supposed to be good. I have had several fill up with 
> what looked like smoke just with filament voltage applied. They went 
> right to the trash.
>
> If you see the white on the glass it is usually a gassy tube.
>
> Dave N7RK

-- 
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|             AM Amateur Radio Operator    NØDGN                   |   
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| Bob Bethman                \\\|///     " The absence of a danger |
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