[Elecraft] KPA-1500 Efficiency As A Function of Input Power

[Victor Rosenthal 4X6GP]

Because the effect of power dissipation over time is temperature 
increase. RTTY has a high duty cycle (100% when you are transmitting), 
compared to 50% for CW and usually something less for SSB (it depends on 
the amount of compression). So more heat is produced when you run RTTY, 
which the amplifier's cooling system has to get rid of. If the cooling 
system can't get rid of it, the temperature rises dangerously and 
components fail.

In the case of the KPA1500, it would seem that there is more power 
dissipated BY THE FINALS at somewhat reduced power levels. But there are 
other components, such as the lowpass filters, which also dissipate some 
power, due to unavoidable losses. This dissipation increases as the 
power output increases. These components would thus get hotter with 
higher power, and they would be more stressed. This is a good reason to 
run less power with RTTY with some amplifiers. I think the designers of 
the KPA1500 took this into account, and you will be fine following the 
published spec.

73,
Victor, 4X6GP
Rehovot, Israel
Formerly K2VCO
CWops no. 5
http://www.qsl.net/k2vco/
On 17/08/2018 16:43, john at kk9a.com wrote:
> So why do most RTTY users run their amps at reduced power?
> 
> John KK9A