[Amps] Life of tubes in ham service

[Jim Thomson]

Date: Wed, 27 Dec 2017 08:57:08 +1030
From: "Leigh Turner" <invertech at frontierisp.net.au>
To: "'Rob Atkinson'" <ranchorobbo at gmail.com>
Cc: "'AMPS'" <amps at 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