From: "Lee Bahr" 
Subject: Re: [drakelist] L4B tube


The solder has melted inside the pin.  When cold or just looking at it all
checks and looks well.  JUST RESOLDER THE FILAMENT PINS!
Lee, w0vt, Houston


Subject: [drakelist] L4B tube


>
> In my L4B amplifier, the tubes burn nicely for a short time, then one of
the
> tubes' filaments go out. I removed the tubes and switched them. Same tube
> goes out after abit. Took that tube out again, checked filament to
filament
> pins, "zero" on the Simpson 260. Also checked for a filament to grid
short,
> (tapping tube didn't change reading) and that reading was
"infinity". So
the
> tube is OK, until it heats up. The solder blob on the pin bottoms are OK.
>
> I think the filaments are getting HOT while I'm transmitting, and possibly
a
> 'fracture' in the filament somewhere, getting hot, expands, then when I'm
in
> the 'listening' mode long enough, the fracture presents itself as an OPEN
in
> the filament line. Comments welcome.
> 73, Gerald, KB7QQ


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