measures wrote:
>
> >
> >My amp uses an Eimac 3CX3000A7, whose cathode is directly heated. (It's a
> >thoriated-tungsten filament, IIRC.) An often-touted virtue of such a tube
> >is that it requires just a couple of seconds of warmup time; in other
> >words, it's "instant-on."
> >
> >My usual mode of operation is "search-and-pounce" DXing. In this mode I
> >may spend 30 minutes scanning the band for a "new one," and then use the
> >amp for a QSO lasting just a minute or two.
> >
> >What's best for the tube?
>
> Leave the fil. off at all times.
There is a paper "Techniques to Extend the Service Life of High Power
Transmitter Tubes" by the Voice of America technical department, in a
PDF file on Burle's web site -
http://www.burle.com/applicatnotepowertub.htm
This shows that for the VOA at least, the reduction in tube failure rate
by leaving on the heaters 24 hours per day was very significant. Tube
costs at one site dropped from $420,00 per year to under $100,000 per
year, with only an extra $15,000 per year in electricity costs. Their
usage pattern is not typical of that of amateurs, and their tubes are a
little larger. However, for me at least, is strong evidence to keep the
heaters on.
--
Dr. David Kirkby Ph.D,
email: drkirkby@ntlwold.com (formally davek@medphys.ucl.ac.uk)
web page: http://www.david-kirkby.co.uk
Amateur radio callsign: G8WRB
--
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