On Fri, 12 Sep 1997 06:37:45 +0000 w8jitom@postoffice.worldnet.att.net
writes:
>> From: STAN <KB8JLV@worldnet.att.net>
To: <amps@contesting.com>
>> Date: Thu, 11 Sep 97 20:05:20 +0000
>Hi Stan,
>
>That tube will work fine with no changes. Ameritron uses them as an
>alternative source.
>
>Be aware that the 3-500ZG has more problems with outgassing than the
>metal anode tube. The graphite anode traps more gas, and Amperex
>seems to not "cook" the tubes as long while pumping them down. Your
>more likely to have a tube flash over with the graphite tubes
>when they are brand new.
>
>You'll see no more output, nor will the tube drive easier or harder
>than the regular tube. What you will have to watch is shutting the
>tube down fast after making a long transmission, because the anode
>releases heat longer after the cooling air is removed. So be sure to
>let the tube wind down for five minutes or so after a long
>transmission before killing the airflow.
>
>IMD will not be greatly different no matter what you do with bias,
>unless you get the tube very near class B. IMD measured about -36 dB
>below one tone at 900 watts PEP with an Amperex tube, and only
>about -38 with a Eimac tube. The Chinese graphite tubes were -31 dB
>below one tone, and also have shown short filament life in the field
>so stay away from them. In any case ALL of the tubes are way better
>than the best solid state radios we have today.
Tom, I dont think it is fair to lump all Chinese tubes together. As
anyone who has followed the magazine articles would know, there are
numerous sources in China.
Over the past several years the quality has improved from some factories
and the bad ones are slowly disappearing.
I have been importing 572B's and 3-500Graphite from a source that has
been very reliable. The glass is thicker and the processing appears much
improved compared to the past.
My data base numbers only in the hundreds, not thousands, but there have
been NO 3-500 returns and only a few 572B's (3 I think).
My own IMD test bed is almost complete and will be capable of up to 150W
Class A from 10KHz to 250MHz. Tests will be Eimac style 2 tone, not ARRL
one tone.
BTW, Richardson is "overstocked" with Amperex and is selling them at $148
according to a recent flyer.
73....Carl KM1H
>73, Tom W8JI
>
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>
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