[AMRadio] Re Viking II Power Mod

[D. Chester]

> Interesting point. 3 X 813's at 2800V and 500 ma delivers a lot more than
> 180 watts if the 813 spec sheet is accurate.
>

That is 180 watts is AM carrier power. The instantaneous peak power for the 
same signal would be more like 720 watts on positive peaks.  That's pretty 
close to what the spec sheet says. The maximum safe carrier output power 
from a linear or grid modulated amplifier is approximately 1/2 the total 
plate dissipation.  A single 813 is rated at 125w plate dissipation.  Three 
of them would have 375 watts dissipation.  Half that is 187.5 watts carrier.

If the amplifier doesn't have enough headroom to pass that much peak power, 
the signal will flat-top on positive peaks, causing the same kind of 
splatter and distortion as overmodulation in the negative direction. More 
carrier output while still maintaining the requisite head room would exceed 
the maximum plate dissipation rating of the 813s.


Don, k4kyv