[1000mp] preference question

[Joe Subich, K4IK]

W5NF asks: 

> Using 75 watts in class A versus straight power out, is there 
> any difference in the heat generated?  Watt thanks

75 watts output in class A is the equivalent of 200 Watts RTTY 
(or AM, FM, etc.) in Class AB.  The BLF-147 is about 35% efficient 
at 120 watts PEP per device (200 Watts for a pair after output 
filter) in class AB at 28 MHz.  

Efficiency is 18% in class A -  400 Watts input (12 amps @ 33 volts)
or 75 watts peak output for the Mark V.

This is the root of the over heating problem with class A ... Yaesu 
specifies 50% duty cycle at 200 watts with a 3 minute transmission 
limit.  Class A operation places as much heat stress on the FETs 
as continuous duty AB operation!  

By the way, the 75 Watt class A spec is for SSB.  For AM, the spec
is 50 Watts of carrier. 

73, 

   ... Joe, K4IK