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The d-c input to r-f output conversion efficiency of the output FETs in the SX transmiitters is 85%.
The total input power from the a-c mains to 100% sine-wave-modulated r-f output power shows an efficiency of about 70%, including a-c power for internal forced air coooling.
Maybe the station where you had to re-strap the transfomers was not the original purchaser? On new orders, Harris always set the taps based on information they got for the installation site from the buyer, during the final test before shipment.