[Heathkit] Suggestion for legal limit AM amp (was Heath Warrior as an AM amplifier)

[Paul Baldock]

To quote W8JI http://www.w8ji.com/amplitude_modulation.htm


In order to reproduce the input faithfully, the amplifier has to be 
loaded to handle the PEAK power. This is normally four times the 
carrier power (or more in some cases). This is because the linear has 
to be "efficiency modulated". A safe estimate is 25% carrier 
efficiency. This means your amp would be making three times the heat 
as carrier power. An SB220 can safely handle about 500 watts of 
steady dissipation (inadequate airflow to fully use the tubes) so it 
is safe at 125 watts carrier when properly tuned.

Very few amplifiers can safely handle legal limit AM. Legal limit AM 
requires 375 watts of carrier power, and three times carrier power 
would be a safe power amplifier dissipation estimate for 
carrier-level heat dissipation. Typically, with a 375-watt carrier, 
over 1100 watts of heat is produced. This takes a lot of air and a 
1200-watt or higher plate dissipation tube. An 8877 at full rated 
airflow, or a 3CX1200 series tube, would work.