I have never seen a 3-500Z fail from an open filament -- except when the
fan does not keep the fil pins cool enough and the solder melts.
However, such tubes can be resoldered.
>I don't have an answer but your post and a couple others I've seen beg this
>question. What is all this worrying about how many times a 3-500z is turned
>on and off?
>
>My ancient Eimacs could care less. What am I missing here?
>
>73,
>Steve wd0ct
>
>
>
>> Here's something I've been pondering, and I'm wondering if it is worth
>pursuit:
>>
>> I have an AL80A amplifier (it's stable, but thanks for asking). The
>3-500Z
>> in it is the original Eimac tube, and does quite well. The amp has an
>> internal Ameritron QSK switch (works great). I don't want to cycle the
>> filament much, so I often turn it on and leave it in "standby" mode while
>I
>> operate, using it only as necessary, which isn't every time I
>> operate. While in standby mode, the filament is running at full voltage.
>> One of the limiting factors in filament life is hours of operation, and
>> they last a lot longer running at lower voltages. Of course, emission is
>> reduced at low voltages, so I wouldn't want to do this while actually
>> generating RF with the amp.
>>
>> Here's the question: Would it be worthwhile to place a small resistor (say
>> something between 0.05 and 0.1 ohm) in series with the filament while in
>> standby? Or is this a no-win scenario, because the small amount of
>thermal
>> cycling would stress the filament enough to send it to an early grave?
>>
>> 73,
>>
>> Kim Elmore, N5OP
>
>
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>
- R. L. Measures, a.k.a. Rich..., 805.386.3734, AG6K,
www.vcnet.com/measures.
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