Just for the output tubes, if one shorts out. It will not take the output with it. Nothing to do with a load. Very rare but you can use a power resistor, added to the output sec. or speaker jack to have dummie load.  Ken did this in 1980, with a rare Plexi 45 100 head. Seen it. 
Rock On
			
			
									
									
						plate diodes
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