[TenTec] Low power DRAIN as well as low output...

[Scott Rosenfeld [N7JI]]

Hi everyone.

The rule of thumb is that maximum transmitter efficiency is achieved at or 
near maximum output power.  Why?

You'll remember that amplifiers, be they tube or solid state, need to be 
biased to bring them into their linear range (if in fact linearity is 
desired).

Remember the venerable 6146B-output rigs, the 520S, 830S, etc?  Remember 
how you had to set bias current to 60 mA?  With no output whatsoever, 
these rigs drew 60 mA at 800VDC for an input power of 48 watts!  This 
translates to ZERO efficiency!

However, at full drive (250 mA), they were good for 110W output (55% 
efficiency).

Unless your amplifier DOES NOT REQUIRE biasing, maximum efficiency will be 
achieved at maximum output.


An output section designed for high power will require a good amount of 
power just to bias it.

A lower power output section?  Smaller transistors, less power to bias it.


Therefore, the way to reduce your input current is to use an output amp 
that is maximized for the range at which you intend to operate.

A 100w rig will almost never be as efficient operating at 5w as a rig with 
a 5 watt output amp (some people actually bypass the high-power amp 
section to achieve this!).

-- 
Scott Rosenfeld  ARS N7JI
541-684-9970  Eugene, OR  Land o' much rain
If you find me on the air, I'm probably in my car
ham at w3eax.umd.edu  http://w3eax.umd.edu/~ham