[R-390] Arcing in 25Z5Ws

[Jim M.]

Could this be caused by higher than normal line voltages?  This happened to
me on a newly purchased radio several years ago.  I concluded the higher
line voltages today was a cause.  Radio was designed for 115, today's
voltages can go over 120 depending on circumstances, putting added stress on
the tubes and other components.  I now have diodes and a high wattage
dropping resistor in the power supply.  Jim N4BE

-----Original Message-----
From: r-390-bounces at mailman.qth.net [mailto:r-390-bounces at mailman.qth.net]
On Behalf Of Dennis Wade
Sent: Sunday, February 17, 2008 2:51 AM
To: R-390 HF Receiver List
Subject: Re: [R-390] Arcing in 25Z5Ws

First of all...please pardon the typo...I do know they're really 26Z5Ws  :)

Both replacement tubes were supposedly NOS...how unusual would it be
to find a shorted tube NOS (although they were packed in 6/62).

         Dennis

On Feb 16, 2008 7:00 PM, Bob Camp <ham at cq.nu> wrote:
> Hi
>
> My *guess* is that you have a filament to cathode short in the '"bad"
> tube.
>
> Bob
>
>
>
> On Feb 16, 2008, at 9:22 PM, Dennis Wade wrote:
>
> > Good evening all,
> >
> >            Recently I flipped the power on to my trusty Motorola
> > R-390A, and instead of the comforting sound of HF radio, I hear
> > nothing, and see a couple of blue-white flashes.  Because I all the
> > covers were on and where I was standing, I couldn't see just where the
> > flashes came from.  When looked at the fuses, the 1/4A B+ fuse was
> > blown.
> >
> >             After a brief detour to replace a cracked fuse holder and
> > a physical inspection, I replaced the B+ fuse and flipped her on
> > again.  Nothing.  The main 3A fuse went too.  Replace that.  Now it
> > lighted up, but no sound.  All the fuses held too.
> >
> >              Now I pay more attention to what's lit and what's not.
> > I noticed both 25Z5s were dark, and after flipping it off again, cold.
> > Replaced both.  Now one is lit, but not the other.  Swap tubes...same
> > tube is lit in the other position, and now the tube starts to arc
> > inside.  Hear a 60 (120?) cycle buzz now too, but nothing else.  Turn
> > power off quickly.  Fuses all held.
> >
> >              Anybody have a guess as to what's going on?  Do I just
> > have some bad rectifiers, or has something else gone south and taking
> > the rectifiers with it.  I'd rather not feed it rectifiers if they're
> > not bad to begin with.
> >
> >                  Opinions welcome.
> >
> >                  Thanks!
> >
> >                     Dennis
> >
> >
> >
> > --
> > Dennis L. Wade
> > KG6ZI
> > Carmichael, CA
> > _____________________________________________________________
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>
>



-- 
Dennis L. Wade
KG6ZI
Carmichael, CA
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