Date: Wed, 27 Dec 2017 08:57:08 +1030
From: "Leigh Turner" <invertech@frontierisp.net.au>
To: "'Rob Atkinson'" <ranchorobbo@gmail.com>
Cc: "'AMPS'" <amps@contesting.com>
Subject: Re: [Amps] Life of tubes in ham service
<Rob, I concur with your succinct sentiments here about transmitting tubes.
The only proviso I would make is the inclusion of a soft-start mechanism on
the filaments to bring them up slowly in a controlled manner at initial
switch-on; and ensure the filament voltage as measured at the socket pins is
tightly within manufacturer's specification.
73
Leigh
VK5KLT
## what else helps is not doing stupid stuff like operating a single 3-500Z
at 600 ma of plate current, like is done in the Ameritron AL-80B.
## Do the maths. To get 1 kw output from a single 3-500Z, with only 2850 vdc
under load, and 60 % eff, requires at least 585 ma.
## when the fil is lit..... the clock is ticking....even with NO drive
applied. After
XXX hrs of fil ON time, the emission will drop off. And you wont be able to
pull
YYY ma anymore. I have run a pair of hb 3-500Zs at 4 kv under load.
Only 500 ma required to get 1300 watts out. It takes a life time to get the
emission
so low that you can no longer pull 500 ma.
## My drake amps,on the other hand, suck 800 ma at 2500 volts, to get the
same PO.
Guess which amps tubes last longer ? Something to be said for maximizing
the B+
provided the RF deck is designed to handle it.
## 585 to 600 ma on a single 3-500Z is beyond reprehensible... unless you
like replacing
tubes.
Jim VE7RF
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