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[TowerTalk] Lots of watts

Subject: [TowerTalk] Lots of watts
From: Nick Pair <>
Date: Mon, 17 Jul 2006 23:43:42 -0700 (PDT)
List-post: <>
Lets see: you get 1700 PEP out with 2500v x .750 mil. a. Even in grounded grid 
that's pretty remarkable.(1875 watts input)
  A few calculations off top of head
  1700 watts on meter minus the 150 drive gives 1550 from tubes.
  That means about 2200 watts times at best 70% efficiency input power, which 
means the current has to be .880 amps..
  If you can't get that efficiency, you have to increase input power to 
  Or to work the other way:
  2200 divide by the .750 a equals 2934 volts on plate.
  If you increase drive you must take into account what the tube grids will 
take and not exceed this too much. A grid can fail easily at or over its rating.
  So you can see by the above that it's best to increase voltage to increase 
power. Then all you have to worry about exceeding the plate dissipation with 
the power lost to inefficiency.(input power times efficiency subtracted from 
input power)
  Of course we have a 1500 watts PEP limit so with 3-500X's you can get by with 
a pretty low plate voltage with 150 watts drive. You can do the calculations 
using the relationships above to see what the minimum voltage would be.(using 
your original 2500 volts at .750 amps times 70% plus your drive equals about 
1463 watts out.
  So most people use the highest voltage they can get, which keeps the current 
low, and run their driver radio at a point below its max where the cleanest 
output occurs.
  All this should be bonded to station ground which is bonded to tower ground 
system. (had to get tower in this some way :-))

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