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


You need to resolder the filament pins to the wires coming out of the
envelope.  The tubes do not get enough cooling and the solder has melted
within the tube base.  (This is not the first time this has happened).
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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