> From: STAN <KB8JLV@worldnet.att.net>
To: <amps@contesting.com>
> Date: Thu, 11 Sep 97 20:05:20 +0000
> I have an ameritron AL-80B that I am replacing the tube in. I have an
> Amperex 3-500 (NIB) I would like to use. Is this tube a suitable
> replacement or is there some modifying that needs to be done to use it.
> Stan/KB8JLV
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.
73, Tom W8JI
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