[R-390] Arcing in 25Z5Ws

[Bob Camp]

Hi

The tubes are *rated* for much higher voltages than they are likely to  
see with any rational line voltage. That's not to say that 40+ year  
old tubes aren't a little gassy ...

Bob

On Feb 17, 2008, at 8:54 AM, Jim M. wrote:

> 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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